JP7800895B2 - Buffer system artificial blood vessel - Google Patents

Description

The present invention relates to a buffer-type artificial blood vessel, and in particular to a buffer-type artificial blood vessel that can be suitably used as a shunt created between an artery and a vein.

The majority of the arterial system branching off from the aorta consists of muscular arteries. With the exception of a few arteries, these muscular arteries comprise arteries that begin at the aorta, pass through small and medium-sized arteries, and then flow into small arterioles just before they flow into arterioles. These muscular arteries are responsible for delivering pulsatile blood pressure and blood flow to the arterioles (inner diameters of 100 to several hundred microns) at the extremities without damping. For example, from the abdominal aorta, with an inner diameter of approximately 25 mm, to the 1-mm-diameter arteries in the limbs, the vascular lumen becomes increasingly smaller and the vascular walls become increasingly thinner, but the blood pressure, pulse amplitude, and mean flow velocity remain almost unchanged from the aorta, remaining at 120/80 mmHg (see Non-Patent Document 1). If blood pressure, pulse pressure, and blood flow were damped and damped at any point between the aorta and the 1-mm-diameter arteries in the limbs, the supply of oxygen and nutrients to the limbs would be reduced, leading to necrosis. In other words, natural arteries function to never dampen or dampen the pulsatile arterial blood flow, which flows at high blood pressure and high speeds.
Since conventional artificial blood vessels are used to replace this function of natural muscular arteries, they have the function of delivering sufficient blood flow downstream to the natural artery connected downstream while maintaining blood pressure and pulsation so as not to attenuate the blood pressure and pulsation of the blood flow. In other words, they are designed and manufactured so that the blood flow flowing inside the artificial blood vessel does not buffer the blood pressure or pulsation when delivering blood.
Thus, conventional artificial blood vessels do not have a shock-absorbing function, and in fact, they eliminate the shock-absorbing function.

The walls of arteries are thick and strong, and even when pulsatile high pressure is applied to the internal blood flow, there is little change in the pulsation of the walls (due to the viscosity of the smooth muscle layer), and there is little generation of turbulence due to wall pulsation or severe fluctuations in friction stress.
On the other hand, thin and soft venous walls have such weak resistance to increased intravenous pressure that even exposure to a state of increased venous pressure that is very weak compared to arterial pressure, such as venous congestion in the lower limbs, can easily lead to serious pathological conditions such as varicose veins, venous thrombosis, and even tissue necrosis due to venous congestion.
Therefore, when arterial blood flows directly from the artery to the vein without passing through the capillaries due to an arteriovenous shunt, and the venous wall is directly exposed to high-speed blood flow with highly pulsatile blood pressure, the intense pulsatile movement of the wall causes blood turbulence and severe fluctuations in stress on the vascular wall. These severe fluctuations are particularly noticeable at the anastomosis between the artery (or artificial blood vessel) and the vein, where there is a significant difference in stiffness between the arterial and venous sides (compliance mismatch).
Therefore, when conventional artificial blood vessels are used as a shunt between an artery and a vein, there is a risk of causing local or systemic pathology, as described in detail below.

For patients with serious kidney disease, hemodialysis is regularly performed, in which blood is extracted from the patient's body, waste products, excess water, minerals, etc. are removed using a dialysis machine, and the blood is then returned to the patient's body.
When performing hemodialysis, a special needle is usually inserted into a vein, but because normal venous blood flow is insufficient for dialysis, it is necessary to divert some of the blood flow from an artery, which has a rich blood flow, into the vein to create a venous blood vessel that can be used for dialysis. Such a blood vessel is called blood access.
Blood access typically involves making an incision in the skin of a limb to expose the artery and vein, making a small incision in the artery and anastomosing the vein to it, and creating a shunt through which a portion of the arterial blood flow is diverted to the vein. In some cases, one end of an artificial blood vessel is anastomosed to the small incision in the artery, and the other end of the artificial vessel is anastomosed to the vein, creating an artificial vessel between the artery and vein, allowing a portion of the arterial blood flow to be diverted to the vein via this artificial vessel.

The dynamics of blood flow on the arterial side are characterized by high blood pressure, large pressure difference pulsations (large pulse pressure), very fast flow velocity, and large flow velocity changes (hemodynamics characteristic of arterial blood as described above will be referred to as "arterial hemodynamics" in the following text). In contrast, the dynamics of blood on the venous side are characterized by low pressure, small pulsatile pressure changes, slow average blood flow velocity, and small flow velocity changes (hemodynamics characteristic of venous blood as described above will be referred to as "venous hemodynamics" in the following text). At the shunt creation site, the venous wall has very low rigidity compared to the arterial wall or the wall of the artificial blood vessel anastomosed to the artery, and the difference in rigidity between the two is significant. Therefore, when arterial blood, which has arterial hemodynamics and does not act on the venous wall under normal conditions, flows from the exit of the artificial blood vessel into a vein with a thin wall and low rigidity, blood flow will occur under normal conditions. This results in uncontrollable blood turbulence and pulsation changes in the venous wall. In other words, it is a state in which stresses that do not occur under normal conditions are exerted. The body's response to this abnormal state is to induce intimal thickening in the veins, which can easily lead to abnormal changes, or pathological changes, such as stenosis, occlusion, varicose veins, and internal thrombosis. Furthermore, if the shunt blood flow state cannot be regulated while still placing a significant burden on the body, it can lead to more widespread local (such as aneurysm formation and stenosis in downstream veins) or systemic (such as steal syndrome due to excessive shunt blood flow or heart failure due to overcirculation) pathologies.
If the conditions on the living body side are favorable, appropriate remodeling occurs as a defensive adaptive response by changes in the rigidity of the venous wall, which may avoid stenosis or occlusion due to intimal thickening, or may even allow the shunt blood flow to self-regulate to a state that does not burden the living body. However, if local conditions such as shunt blood flow rate or anastomotic shape or systemic conditions (diabetes, hypertension, arteriosclerosis, blood properties, etc.) are poor, the range of appropriate defensive adaptive responses may be exceeded, resulting in a pathological biological response and causing local and systemic pathologies. In particular, artificial blood vessels are more rigid than natural arteries, so the difference in rigidity between them and veins is significant, preventing the appropriate defensive adaptive responses described above, often resulting in the local or systemic pathologies described above.

To prevent such pathological conditions, vascular banding has been performed (Non-Patent Document 2). Patent Document 1 discloses a covering for reinforcing natural veins used as surgical implants, which is a knitted fabric net covering made by forming a seamless, tubular, and substantially pile-less knitted fabric. Patent Documents 2 and 3 disclose that an arteriovenous graft (AVG) wrapped with a restrictive fiber matrix of a biodegradable polymer exhibited pulsatile radial deviation similar to that of the carotid artery.
However, the above-mentioned vascular banding has not been able to sufficiently prevent lesions such as intimal hyperplasia (Non-Patent Document 2).

Special Publication No. 2004-535896 Special Publication No. 2010-516437 Special Publication No. 2013-509258

Shinji Maeda: Educational Lecture: Blood Rheology and Physiological Functions, Part 1: Fundamentals of Hemodynamics and Blood Viscosity, Nissei Shishi 234-244, 66, 7-8, 2004 Hiroaki Haruguchi, "I. Blood Access: Problems Associated with Blood Flow Insufficiency," Journal of the Japanese Society of Dialysis Therapy, Vol. 15, No. 1, 68-70, 2000

In conventional vascular banding, the reinforced venous wall is modified (arterialized) to resemble the natural arterial wall. However, as mentioned above, natural arteries function to never dampen or buffer pulsatile arterial blood flow at high blood pressures and high speeds. Therefore, when blood passes through the reinforced area and flows into an unreinforced vein, the blood pressure and pulsation are not dampened and it is delivered downstream. This simply postpones the problem to be solved downstream and does not fundamentally resolve the cause of intimal thickening. To resolve this, it is necessary to gradually dampen and reduce arterial hemodynamics (hemodynamics with high pressure, large pulsatile pressure changes, fast flow velocity, and large flow velocity changes) from the anastomosis downstream, so that the venous wall at the most downstream side is only acted upon by venous hemodynamics (sufficiently reduced mean flow velocity, flat flow velocity changes, sufficiently low blood pressure, and small pressure changes).
The present invention has been made in consideration of the above circumstances, and aims to provide a buffer-type artificial blood vessel that can prevent intimal thickening by buffering and reducing the blood flowing through the lumen of the artificial blood vessel from arterial hemodynamics to a range that can be tolerated by a healthy venous wall (low-pressure buffering of hemodynamics) while delivering the blood to a downstream vein.

After extensive research, the inventors have discovered that the above problems can be solved by adopting the following configuration.

That is, the buffer system artificial blood vessel of the present invention is a buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, and is characterized in that the function of buffering the blood flow is a low-pressure buffering function that reduces the pressure and pulsatile pressure changes, and/or the flow velocity and magnitude of the change in flow velocity, of the blood flowing in from the arterial side, and allows it to flow out to the venous side.
A typical example of a buffer system artificial blood vessel of the present invention is a shunt constructed between an artery and a vein, but it also includes cases where the shunt is constructed between an artery and a vein at a location where the vein downstream of the construction site has undergone pathological changes such as stenosis due to arterial blood flow, or at a location where there is a risk of such pathological changes occurring.

The buffer cylinder of the buffer-system artificial blood vessel of the present invention differs from the normal flow path section upstream of it in that it exhibits a gradient change in shear stress caused by blood flowing through the lumen of the buffer cylinder, pressure perpendicular to the artificial blood vessel wall, and the range of change associated with blood flow volume, flow velocity, and pulsation. In other words, it has the function of delivering blood to the downstream vein while buffering and reducing the arterial hemodynamics of the blood flowing through the lumen of the buffer cylinder. This function suppresses elastic incompatibility in the wall of the vein anastomosed downstream, as well as blood turbulence and high flow velocity, and prevents narrowing or occlusion of the blood vessel lumen due to intimal hyperplasia and thrombus formation.

The buffer-type artificial blood vessel of the present invention exhibits the above-mentioned performance through the following two mechanisms.
The first is the buffering effect of the physical structure of the buffer artificial blood vessel at the time of its creation, which acts to buffer arterial hemodynamics, and can be called a "physical buffering effect." The second is the biological effect of the elasticity of the buffer artificial blood vessel on the shunt vein, which induces the vein itself to remodel (remodel) its own structure and function into a buffer system vessel, which can be called a "biological buffering effect."
Although buffering blood vessels can be effective with just one of the above-mentioned "physical buffering" and "biological buffering" functions, it is thought that in actual applications to living organisms, both functions often work together to achieve a buffering effect. In this document, for the sake of clarity, we will explain both separately.

The former, "physical buffering effect," will be explained first below, and the latter, "biological buffering effect," will be discussed later.

1 is an overall view showing a buffer-type artificial blood vessel according to a first embodiment of the present invention. 1 is a side view showing a buffer-type artificial blood vessel according to a first embodiment of the present invention. FIG. FIG. 10 is a side view showing a buffer-type artificial blood vessel according to a second embodiment of the present invention. FIG. 10 is a side view showing a buffer-type artificial blood vessel according to a third embodiment of the present invention. FIG. 10 is a side view showing a buffer-type artificial blood vessel according to a fourth embodiment of the present invention. FIG. 10 is a side view showing a buffer-type artificial blood vessel according to a fifth embodiment of the present invention. FIG. 10 is a side view showing a buffer-type artificial blood vessel according to a sixth embodiment of the present invention. FIG. 10 is a cross-sectional view of a buffer cylinder of a buffer-system artificial blood vessel according to a sixth embodiment of the present invention. FIG. 10 is a side view showing a buffer-type artificial blood vessel according to a seventh embodiment of the present invention. FIG. 13 is a cross-sectional view of a buffer cylinder of a buffer-system artificial blood vessel according to a seventh embodiment of the present invention. FIG. 1 is a perspective view showing a sample for measuring an elasticity index. FIG. 2 is a plan view of a sample for measuring an elasticity index, viewed from above. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. FIG. 1 is an explanatory diagram of an AV shunt prepared in an animal experiment according to an embodiment of the present invention. FIG. 1 is a side view showing the basic shape of a trumpet-shaped buffer cylinder. FIG. 10 is an explanatory diagram of the relative lengths of the buffer cylinder in a trumpet-shaped buffer cylinder. 1 is a photograph of EvG staining in the evaluation test of Example 27.

Preferred embodiments of the buffer-type artificial blood vessel according to the present invention will be described in detail below, with reference to the drawings as appropriate. However, the scope of the present invention is not limited to these descriptions, and modifications other than those exemplified below may be made as appropriate without departing from the spirit of the present invention.

First Embodiment
1 and 2 show a buffer-type artificial blood vessel 1 according to a first embodiment of the present invention.
The buffer system artificial blood vessel 1 is generally tubular and open at both ends. One end of the buffer system artificial blood vessel 1 is anastomosed to a small incision in the artery A, and the other end is anastomosed to the vein V, so that the buffer system artificial blood vessel 1 is constructed between the artery A and the vein V.
The white arrows in Figure 1 indicate the flow of blood. A portion of the blood flows from the artery A into the buffer system artificial blood vessel 1, passes through the buffer system artificial blood vessel 1, and is buffered and reduced from the arterial hemodynamics to a range that can be tolerated by a healthy venous wall, and then flows out into the vein V. Blood can be removed and returned from the artificial dialyzer D.

The material of the buffer-type artificial blood vessel 1 may be the same as that of a general artificial blood vessel.
Specifically, the material of the buffer-type artificial blood vessel 1 may be any of synthetic polymers, natural polymers, and hybrids thereof, and may also be porous, such as woven fabric, knitted fabric, nonwoven fabric, or sponge-like material.
Examples of synthetic polymers include fluorine-based polymers such as expanded polytetrafluoroethylene (ePTFE) and polytetrafluoroethylene (PTFE), polyolefins such as polyethylene and polypropylene, polyesters, polyamides, acrylic polymers, aromatic polyether ketone resins such as PEEK, polyester elastomers such as polyether polyamide resins and polyester polyols, polyimide resins, acrylic polymers, polyurethanes, silicones, and copolymers thereof. Biodegradable materials, such as bioabsorbable polymers including aliphatic polyesters such as polylactic acid, polyglycolic acid, caprolactam, polybutylene succinate, and polyhydroxyalkanoic acid; aliphatic polyethers such as polyethylene glycol; and polyvinyl alcohol, as well as copolymers thereof, may also be used.
Examples of natural polymers include silk, cotton, konjac components, spider silk components, as well as bioabsorbable elastin, alginic acid, chitosan, collagen, gelatin, and the like.
As elastic fibers, in addition to natural elastomers, synthetic fibers such as urethane-based and silicone-based fibers, polytrimethylene terephthalate fibers and polybutylene terephthalate fibers, side-by-side fibers that combine two different types of polymers, and woolly processed fibers (yarns) may also be used.
Furthermore, bioabsorbable materials and metals may also be used.
When woolly processed fibers are used, those made of polyamide (nylon), polyester (tetron), or bioabsorbable polylactic acid are preferably used.

The buffer system artificial blood vessel 1 includes a buffer cylinder 10 having a buffer function. The buffer system artificial blood vessel may be composed of only this buffer cylinder 10, or may be composed of both this buffer cylinder 10 and a normal flow path section 20, as in this embodiment.
The normal flow path section 20 has the basic shape of the buffer system artificial blood vessel 1, and by reducing the thickness of the tube wall of this normal flow path section 20, changing the diameter size or cross-sectional shape of the diameter, or changing the material, a buffer cylinder 10 is formed continuously on the vein V side in principle.

The dimensions of the flow path section 20, such as the inner diameter, outer diameter, and thickness, can typically be similar to those of a typical artificial blood vessel. While these dimensions vary depending on the site of use in the body and the material, they can be, for example, approximately 2-8 mm inner diameter, 3.5-11 mm outer diameter, and 0.5-2 mm thick. When used for dialysis, which is typically performed three times a week, the strength and thickness must be sufficient to withstand repeated punctures with a thick needle in two places three times a week.

The buffer cylinder 10 on the vein V side is preferably formed as close to the vein V as possible, but this is not necessarily required. The reason why it is preferable to form it as close to the vein V as possible is that, for blood removal, the normal flow path section 20 before passing through the buffer cylinder 10 is usually used, and the farther the buffer cylinder 10 on the vein V side is from the vein V, the shorter the area used for blood removal often becomes. The reason why this is not necessarily required is that the opposite may sometimes be desirable depending on the systemic pathology or local pathology.
The buffer cylinder 10 on the vein V side has an expanded diameter portion 11 on the vein V side, the diameter of which expands from the artery A side to the vein V side.
Because the diameter is enlarged at the enlarged diameter portion 11, the blood flowing in from the artery A side is buffered in arterial hemodynamics and flows out from the vein V side.

The degree of diameter change of the expanded diameter section 11 is not particularly limited, but for example, the maximum diameter on the vein V side can be approximately 1.01 to 5 times the minimum diameter on the artery A side, and more preferably 1.2 to 2.5 times. The diameter expansion angle can be approximately 1 to 90°, and more preferably 10 to 70°, and even more preferably 15 to 60°. Although this depends on factors such as the elasticity of the wall, if the diameter change is too large, problems such as turbulence may occur. Although this also depends on factors such as the elasticity of the wall, if the diameter change is too small, the buffering effect may be insufficient. Furthermore, it is desirable for the angle at which the diameter changes to be a smoothly changing curve, as this is more effective at preventing turbulence.

The buffer cylinder 10 also has an elastic portion 12 that is more elastic (easily stretchable) than the normal path portion 20. This is also effective in buffering and reducing arterial hemodynamics.
One method for increasing elasticity is to make the thickness of the buffer cylinder 10 thinner than that of the normal path portion 20. Specific methods include, for example, making the buffer cylinder 10 thinner than the surrounding area when molding the buffer system artificial blood vessel 1, or making the buffer system artificial blood vessel 1 partially laminated (for example, molding a highly elastic resin material such as polyurethane thin to create the overall base shape, and then laminating a resin material such as a fluorine-based polymer on areas other than the buffer cylinder 10 to make the wall thicker).
Although the innovation in this embodiment is implemented in the enlarged diameter portion, this innovation may also be implemented in the straight lumen portion other than the enlarged diameter portion.

Second Embodiment
FIG. 3 shows a buffer system artificial blood vessel 2 according to a second embodiment of the present invention.
The buffer cylinder 10 of the buffer-system artificial blood vessel 2 has a narrowed portion 13 with a reduced diameter upstream of the enlarged diameter portion 11 .
The other configurations are the same as those of the buffer-type artificial blood vessel 1, and therefore the explanation will be omitted.

Here, arterial blood pressure is expressed as cardiac output (Q) x peripheral resistance (R), and according to Poiseuille's law, peripheral resistance (R) is proportional to blood viscosity (η) and inversely proportional to the fourth power of the blood vessel radius (r) (Educational Lecture: Blood Rheology and Physiological Function, Lecture 1: Fundamentals of Hemodynamics and Blood Viscosity: Maeda Shinji, Journal of the Physiological Society of Japan, Vol. 66, No. 7-8, 234-244, 2004). In other words, in natural arteries or more rigid artificial blood vessels, a 10% reduction in blood vessel diameter increases resistance by (1/0.9)^4 ≒ 1.5 times, and a 10% expansion in blood vessel diameter decreases resistance by (1.0/1.1)^4 ≒ 0.68 times = 68%.

A very schematic and simplified explanation follows.
As a first example, consider an arteriovenous shunt constructed by side-to-end anastomosing a conventional artificial blood vessel to a natural artery. The inner diameter of a conventional artificial blood vessel is typically 6 mm, and a vein is anastomosed end-to-end to the downstream end of the sufficiently long conventional artificial blood vessel. The vein is free of surrounding tissue, leaving only the venous wall tissue. Under normal arterial pressure, it expands to more than 6 mm. Because conventional artificial blood vessels are designed without any buffering function for blood pressure or blood flow, the arterial hemodynamics act on the venous wall without any buffering at the downstream end of the artificial blood vessel (i.e., the point where blood flows out of the artificial blood vessel into the vein). The venous wall expands and contracts repeatedly due to the arterial hemodynamic pressure pulsation, causing changes in venous diameter. Generally, the flow velocity and resistance of venous blood under physiological conditions (normal, natural, healthy conditions are medically referred to as physiological conditions; abnormal conditions are referred to as pathological conditions) are significantly lower than those under arterial hemodynamic conditions. Therefore, the stress and changes acting on the venous wall under arterial hemodynamics acting on the anastomotic vein are much greater than those under physiological conditions. A venous wall placed in this abnormal, or pathological, state can be a major cause of pathological changes such as intimal hyperplasia and stenosis as a result of pathological reactions.

As a second example, consider a buffer-type artificial blood vessel with a sufficiently long conventional artificial blood vessel, but with a short, expanded diameter section (buffer section) with a diameter expanded by only 10% at the most downstream end. In this case, the expanded diameter section is located downstream of the conventional artificial blood vessel, and a vein similar to that of the conventional artificial blood vessel described above is anastomosed end-to-end to the downstream end of the expanded diameter section. Since the diameter of the conventional blood vessel, which occupies the majority of the area upstream of the expanded diameter section, determines the actual resistance of this artificial blood vessel, we can assume that the hemodynamics of the conventional artificial blood vessel portion immediately before the inflow to the expanded diameter section will be virtually unchanged with or without the expanded diameter section, and will be virtually unchanged from the most downstream section of the conventional artificial blood vessel in the first example. Compared to the section immediately before the inflow to the expanded diameter section, resistance in the expanded diameter section (i.e., the buffer section with a 10% expanded diameter) will be reduced by 68%. However, the resistance in this area is greater than the resistance of the vein anastomosed to the downstream end of the enlarged section, and blood flow is largely determined by the resistance of the sufficiently long conventional artificial blood vessel upstream of this enlarged section and systemic blood pressure. Therefore, in the enlarged section, blood pressure and blood flow are directed halfway between the upstream conventional artificial blood vessel section and the vein section. In other words, this is the buffering effect on blood flow conditions at the enlarged section. If a very rough estimate is allowed, a buffering effect is expected that will reduce changes in blood pressure and blood flow, as indicated by a decrease in resistance, by approximately 68%.

As a third example, consider a buffer-type artificial blood vessel with a sufficiently short narrowed section (10% smaller in diameter) located downstream of a sufficiently long conventional artificial blood vessel, and an expanded section (10% larger in diameter than the conventional artificial blood vessel) immediately downstream of this narrowed section. The overall blood flow through the artificial blood vessel is reduced due to increased resistance caused by the narrowed section (a very rough estimate is to 1/1.5, or 67%, of that of the conventional artificial blood vessel). However, because blood pressure is largely determined by systemic blood pressure, the change in blood pressure is small, and the dominant changes are the increased resistance and the decrease in average flow velocity through the conventional artificial blood vessel section (i.e., the flow rate of the entire artificial blood vessel). Subsequently, due to the effect of the expanded diameter section (1.1 times larger than the conventional artificial blood vessel section and 1.1 x 1.1 times larger than the narrowed section), the blood pressure and flow velocity at the expanded diameter section are guided to somewhere between those of the conventional artificial blood vessel section and the venous section. In terms of blood flow dynamics, this expanded area is a "buffer pond" of the same size as in the second example, but because the blood flow flowing in from the narrowed area is a "smaller river," the buffering effect of the expanded area is relatively greater, demonstrating a greater buffering effect than in the second example, and it is expected that arterial blood flow dynamics will be buffered by roughly 45%.

As a fourth example, consider a buffer-type artificial blood vessel that has an expanded diameter section downstream of a conventional artificial blood vessel that is 10% larger in diameter than the conventional artificial blood vessel, and a relatively narrow section with a smaller diameter than the expanded diameter section just downstream of that. The expanded diameter section, which is 10% larger in diameter, acts as a "buffer basin" that buffers the inflow of arterial blood flow, while the relatively narrow section downstream of that acts as an "outlet gate," further enhancing the buffering effect of the buffer basin. In this case, the buffering effect is maximized when the expanded diameter section that acts as a buffer basin and the relatively narrow section downstream of it that acts as an "outlet gate" have appropriate elasticity.

As described above, by appropriately combining an expanded diameter section and a narrow section, such as by providing a narrow section and an expanded diameter section downstream thereof, or conversely by providing a narrow section downstream of an expanded diameter section, the buffering effect can be further enhanced.
Therefore, by providing the narrowed portion 13 in addition to the diameter expansion and elasticity change, the effect of buffering and reducing arterial hemodynamics can be further enhanced.
Furthermore, by combining multiple buffer means in this way, a high buffer effect can be obtained while reducing the risk of turbulence, etc., compared to when relying on a single buffer means. By efficiently obtaining a buffer effect, the length of the buffer cylinder 10 can be shortened, and the normal flow path section 20 used for puncturing can be made longer.
The diameter change of the narrow portion 13 is not particularly limited, but for example, the minimum diameter at the center of the narrow portion 13 can be about 99% to 5% of the inner diameter of the normal path portion 20, more preferably about 90% to 30%, and even more preferably about 80% to 40%. If the diameter change is too sudden, problems such as turbulence may occur. If the degree of diameter change is too small, the buffering effect may be insufficient.

Third Embodiment
FIG. 4 shows a buffer system artificial blood vessel 3 according to a third embodiment of the present invention.
The buffer system artificial blood vessel 3 has a buffer cylinder 10 formed not only on the vein V side but also on the artery A side, and the buffer cylinder 10 on the artery A side has a narrowed portion 13 whose diameter decreases from the vein V side to the artery A side. The end of the narrowed portion 13 on the artery A side is open and is anastomosed to the small incision in the artery A.
In this way, a narrowed portion may be provided on the arterial side.

Fourth Embodiment
FIG. 5 shows a buffer system artificial blood vessel 4 according to a fourth embodiment of the present invention.
The buffer-type artificial blood vessel 4 has a spiral-shaped lumen in the enlarged diameter portion 11 .
The other configurations are the same as those of the buffer-type artificial blood vessel 1, and therefore the explanation will be omitted.
In the buffer system artificial blood vessel 4, the lumen of the expanded diameter portion 11 is spiral, and therefore in addition to the buffering effect due to the expanded diameter and change in elasticity, the buffering and reducing effect on arterial hemodynamics can be further enhanced.
As described above, by combining multiple buffering means, it is possible to obtain a high buffering effect while reducing the risk of turbulence and the like compared to relying on a single buffering means, and as a result, it is possible to shorten the length of the buffer cylinder 10 and ensure a long normal flow path section 20 that can be used for puncturing.
Although the innovation in this embodiment is implemented in the enlarged diameter portion, this innovation may also be implemented in the straight lumen portion other than the enlarged diameter portion.

Fifth Embodiment
FIG. 6 shows a buffer system artificial blood vessel 5 according to a fifth embodiment of the present invention.
The buffer system artificial blood vessel 5 has a buffer cylinder 10 in which portions with different elasticity are combined in a patch-like manner. It differs from the buffer system artificial blood vessel 1 in that it has a plurality of elastic portions 12, 12... that are highly elastic (easily stretchable). That is, while the entire buffer cylinder 10 of the buffer system artificial blood vessel 1 is highly elastic, the buffer system artificial blood vessel 5 has a plurality of elastic portions 12, 12... partially arranged on the buffer cylinder 10, with the elastic portions 12, 12... and other portions intermixed in a patch-like manner. As with the buffer system artificial blood vessel 1, the elastic portions 12, 12... can be formed by making the thickness of the elastic portion 11 thinner than the surrounding area or by using a different material.
In the buffer-type artificial blood vessel 5, the elastic portions 12 are diamond-shaped, but may have other shapes. However, from the viewpoint of achieving a balanced buffer effect and preventing turbulence, it is preferable that the elastic portions have a shape and arrangement that is somewhat regular.
Although the innovation in this embodiment is implemented in the enlarged diameter portion, this innovation may also be implemented in the straight lumen portion other than the enlarged diameter portion.

Sixth Embodiment
7 and 8 show a buffer-type artificial blood vessel 6 according to a sixth embodiment of the present invention. Figures 8(a) to 8(c) are cross sections taken along lines aa, bb, and cc in Figure 7, respectively.
The buffer system artificial blood vessel 6 is a buffer system artificial blood vessel 1 to which a different kind of innovation has been applied.
As shown in Figures 8(b) and 8(c), the expanded diameter section 11 of the buffer-system artificial blood vessel 6 has an elliptical cross section, with the tube wall on the major axis side being thicker and the tube wall on the minor axis side being thinner.
The thin wall on the short diameter side provides a buffering effect, while the thick wall on the long diameter side is intended to prevent a series of risks, such as compression, narrowing, and blockage of the blood vessel. The reason for making the wall on the long diameter side thicker than on the short diameter side is that with conventional artificial blood vessel installation methods, if the wall on the long diameter side is thin, the buffered blood tends to flow at a slower rate, and if that part is compressed and narrowed, blood clots can easily form, and in the worst case scenario, the risk of permanent blockage increases.
However, the reverse (thicker tube wall on the longer diameter side and thinner tube wall on the shorter diameter side) is also possible. This is because sometimes the positional relationship between the skin and fascia requires an installation that is reversed from normal. Note that although the innovation in this embodiment is made in the enlarged diameter section, this innovation may also be made in the straight lumen portion that is not in the enlarged diameter section.

Seventh Embodiment
9 and 10 show a buffer-type artificial blood vessel 7 according to a seventh embodiment of the present invention. Figures 10(a) to 10(c) are cross sections taken along lines aa, bb, cc, and dd in Figure 9, respectively.
The buffer-type artificial blood vessel 7 has a similar structure to the buffer-type artificial blood vessel 6, but differs in that the thickness of the tube wall on the major diameter side is gradually changed. As shown in Figures 10(c) and 10(d), the tube wall on the major diameter side located at the upper side as viewed in the figure is thin-walled in the c-c cross section, gradually changes in thickness, and becomes thick-walled in the d-d cross section. The tube wall located at the lower side as viewed in the figure is the opposite of the tube wall located at the upper side; it is thick-walled in the c-c cross section, gradually changes in thickness, and becomes thin-walled in the d-d cross section, resulting in a well-balanced structure overall.

[Preferable conditions for buffer-type artificial blood vessels]
<X% Elasticity Index>
In the above description of each embodiment, the elasticity of the buffer cylinder 10 has been mentioned, and the following "X% elasticity index" can be used as an index for this elasticity. In the present invention, the "X% elasticity index" refers to the value defined below.

(Method for measuring X% elasticity index)
The X% elasticity index is determined for a sample of a buffer cylinder having an axial length of 5 mm when the inner diameter expands by X% from its natural state. The method for measuring the elasticity index will be described with reference to Figures 11 and 12. Figure 11 shows a perspective view of a measurement sample 100 for the elasticity index, and Figure 12 shows a plan view of the measurement sample 100 shown in Figure 11 when viewed from above.
[Measurement method]
The buffer cylinder is cut out in the axial direction up to a portion extending 5 mm to prepare a cylindrical sample 100 having an axial length of 5 mm. The cylindrical sample 100 is cut out along a cut surface perpendicular to the axial direction, i.e., a cutting line in the circumferential direction, so as to obtain a cylindrical sample 100 having an axial length of 5 mm and continuous around the entire circumference. However, in a buffer-type artificial blood vessel in which cuts are formed in the buffer cylinder and the wall can be separated along the cuts, the wall becomes discontinuous at the cuts, making it impossible to prepare a "cylindrical sample that is continuous around the entire circumference." Therefore, a cylindrical sample that is continuous around the entire circumference except for the cut portions of the wall is cut out.
A first pin 101 and a second pin 102, each with a diameter d of 0.75 mm, are inserted into the inner cavity of the cylindrical sample 100 parallel to the axial direction of the cylindrical sample 100. The first pin 101 is fixed, and the second pin 102 is pulled radially outward of the cylindrical sample 100 with a force F. When the distance between the first pin 101 and the second pin 102 is L, the force F _1+0.01X when πd+2L is (1+0.01X) times the circumferential length of the cylindrical sample 100 in its natural state is divided by the strain [((1+0.01X)-1.0)/1.0], and the value obtained is the X% elasticity index.
Here, the distance L between the first pin 101 and the second pin 102 is the distance from the center of the first pin 101 and the second pin 102, as shown in Figure 12. The inner diameter of the cylindrical sample 100 is equal to the sum of 1/2 the circumference πd of the first pin 101, 1/2 the circumference πd of the second pin 102, and twice the distance L between the first pin 101 and the second pin 102, i.e., πd + 2L. For example, when the inner diameter of the cylindrical sample 100 expands 30% from its natural state, that is, when πd + 2L becomes 1.3 times the circumferential length of the cylindrical sample 100 in its natural state, the force F _1.3 pulling the second pin 102 can be divided by the strain [(1.3 - 1.0)/1.0] to obtain a 30% elasticity index.

If it is difficult to measure using the above-mentioned measurement method using a cylindrical sample, the X% elasticity index can be measured using a strip-shaped sample developed from the cylindrical sample instead of the cylindrical sample.
Specifically, a cylindrical sample is unfolded to prepare a strip-shaped sample, and both ends of the sample in the longitudinal direction are gripped with two jigs and pulled outward. The distance (L) between the gripping positions of the jigs is recorded when no force is applied to the jigs (natural state), and then the distance (L + S) between the gripping positions of the jigs when a force is applied and the jigs are pulled is determined. The value S obtained by subtracting L from L + S is divided by L (S ÷ L × 100 = X), i.e., the strain (X) is calculated. In addition, the force F 1 + 0.01X when both ends of the strip-shaped sample are pulled and the distance between the gripping positions of the jigs becomes ( ₁ + 0.01X) times the distance between the jigs in the natural state is divided by the strain [((1 + 0.01X) - 1.0) / 1.0] to obtain a value. Doubling this value corresponds to the X% elasticity index obtained by the above measurement method using a cylindrical sample.
For example, in Example 30 described below, the above measurement method using a cylindrical sample was not possible, so the elastic index was measured using the following method. Specifically, a single zigzag iron wire was held at both ends with two jigs while the wire was still in a heat-treated, tubular shape, and the jigs were pulled in a direction to straighten the zigzag wire. First, the distance (L) between the gripping positions of the jigs was recorded when no force was applied to the jigs (natural state). Next, the distance (L + S) between the gripping positions of the jigs when the wire was pulled with force was determined. The value S, obtained by subtracting L from L + S, was divided by L (S ÷ L × 100 = X), i.e., the strain (X). In addition, in that state, that is, when the zigzag iron wire is pulled and the distance between the gripping positions of the jigs becomes (1+0.01X) times the distance between the jigs in the natural state, the force F _1+0.01X is divided by the strain [((1+0.01X)-1.0)/1.0], and the obtained value is doubled to obtain the X% elasticity index.

When samples are cut out from the buffer cylinder, if the values differ depending on the cut-out portion, the lowest value of the sample shall be taken as the X% elasticity index of the buffer cylinder.
Furthermore, if the buffer cylinder to be used for measurement is, for example, trumpet-shaped and a uniform cylindrical sample with an axial length of 5 mm cannot be cut out, a straight cylindrical buffer cylinder made in the same manner as the part to be measured can be prepared, and the elastic index of the sample with an axial length of 5 mm of this buffer cylinder can be measured using the method described above.
Furthermore, when the buffer cylinder used for measurement is an artificial blood vessel reinforced with, for example, a spiral reinforcing material called a reinforcing material or a support (support), or an artificial blood vessel made of knitted or woven fabric, cutting out a cylindrical sample 5 mm in axial length and pulling it often results in fraying of the support or fabric. In this case, therefore, a cylindrical sample having an appropriate axial length of Y mm (e.g., 25 mm) is cut out, the elasticity index is measured using the above method, and the value is divided by Y/5 (e.g., if Y=25, then 25 mm ÷ 5 mm = 5) to determine the elasticity index per 5 mm.

Among the X% elasticity indices defined above, the 30% elasticity index, 60% elasticity index, and 100% elasticity index are particularly useful as indicators. The reasons for this are as follows:

First, the reason for setting the elasticity index at 30% will be explained below.
As a preliminary study, the inventors created an arteriovenous shunt between the carotid artery and jugular vein of a dog as an experimental model similar to that of a human arteriovenous shunt, and conducted an experiment on the expansion of the venous side when arterial blood flow flows from the arterial side to the venous side through this arteriovenous shunt.
To create an arteriovenous shunt, a 60 mm long aluminum tube with a circular lumen, constant diameter, and rigidity (i.e., no elasticity of the wall) was placed over the vein. The aluminum tube had a spiral or helical layered wall, allowing for flexible adjustment of the inner diameter within a narrow range. The aluminum tube was then moved to the most upstream shunt vein connected to the artery, covering the entire vein along a 60 mm length. A vascular clamp was then placed on the upstream artery to block arterial blood flow, and the vein's outer diameter was measured in the state where a small amount of blood remained inside the vein (hereinafter referred to as the "natural state"). The vascular clamp was then removed, allowing arterial pressure to flow from the upstream artery into the vein. The vein's outer diameter was then measured immediately downstream of the tubing-covered portion. Next, an ultrasonic blood flow meter was used to evaluate whether the arterial blood flow dynamics through the vein at the measured outer diameter were buffered. The results showed that when the inner diameter of the coated aluminum tube was set to 1.3 times or more the outer diameter of the natural vein, i.e., when the play between the inner diameter of the tube and the natural vein wall was set to 30% or more of the natural vein diameter, the blood flow dynamics immediately downstream of the coated portion of the tube were buffered. On the other hand, when the inner diameter of the coated tube was set to 1.15 times or less the outer diameter of the natural vein, i.e., when the play between the inner diameter of the tube and the vein wall was set to 2/3 times 30% (=20%) or less of the natural vein diameter, no buffering effect was observed. While these experimental results are only for reference, when considering buffering of arterial blood flow, it is believed that when the natural vein expands to 1.3 times or more its original diameter, a buffering effect due to the elasticity of the vascular wall is more likely to be observed than when the expansion is less severe. Using this data as a guideline, the inventors determined that the elasticity index of the buffer system blood vessels when the inner diameter is expanded by 30% (30% elasticity index) is useful as an indicator of the vascular wall elasticity involved in the buffer function when the expansion of the artificial blood vessel is relatively small.
Although vein expansion was measured by the expansion of the outer diameter, measuring the inner diameter does not change the degree (%) to which the vascular wall has expanded from its original size. Therefore, when measuring the elasticity index, the expansion of the inner diameter was used as an indicator.

Next, the reason for setting the elasticity index at 100% will be described.
Similar to the experiment for establishing a 30% elasticity index, an arteriovenous shunt was created in a dog, and the outer diameter of the vein in its natural state was measured. Next, without covering the vein with any aluminum tube, the vascular clamp that had been attached to the upstream artery to block arterial blood flow was removed. Arterial blood flow was then allowed to flow from the artery upstream of the shunt through the arteriovenous shunt into the vein, and the vein immediately downstream of the shunt was observed to dilate due to the inflow of blood. The vein diameter immediately downstream of the shunt was then immediately measured. As a result, it was observed that the vein diameter, upon receiving arterial blood flow, always dilated to more than twice its natural diameter (a state in which the dilation width was increased by 100% compared to the natural state). However, less than half of the vein diameters dilated to more than three times its natural diameter (a state in which the dilation width was increased by 200% compared to the natural state). Therefore, the 100% elasticity index, which is the elasticity index when the vein is dilated to twice its natural diameter, was determined to be useful as an elasticity index of the vascular wall involved in the buffering effect when the vein is strongly dilated.

Next, the reason for setting the 60% elasticity index will be explained.
Arterial blood pressure acts as a pulsating wave, alternating between very high blood pressure (systolic pressure) and relatively low blood pressure (diastolic pressure). As mentioned above, the 30% elasticity index (30% elasticity index) is used as the elasticity index of the buffer system vessels. It is useful as an index of vascular wall elasticity, which contributes to the buffering function when the artificial blood vessel is relatively small in dilation, i.e., when blood pressure is relatively low. Furthermore, the 100% elasticity index, which is the elasticity index when the vein is dilated twice its natural diameter, is used as the elasticity index of the vascular wall, which contributes to the buffering effect when the vein is strongly dilated, i.e., when high blood pressure is applied. The buffering of arterial blood flow in the buffer vascular system is actually the combined result of the buffering effect under all blood pressure conditions between these two conditions, i.e., all dilation conditions between 30% and 100%. Therefore, we have determined that a 60% elasticity index, which is approximately halfway between 30% and 100%, is useful as an index of vascular elasticity involved in buffering function from another perspective, that is, as an elasticity index of the vascular wall involved in the buffering effect in the overall average dilation state, or, if we may say, the overall average blood pressure state.

In order to obtain a cushioning effect by the elastic force (ease of stretching) of the buffer cylinder 10, it is preferable that the 30% elasticity index of the buffer cylinder 10 defined above is 11 N or less, and more preferably, it is 1.6 N or less in order to exhibit a cushioning effect solely through uniform wall elasticity, even in the case of a buffer cylinder with unfavorable conditions such as a straight buffer cylinder with no change in inner diameter or wall elasticity.
The lower the 30% elasticity index of the buffer cylinder 10, the more advantageous it is for the buffer effect to be exhibited.
In addition, a lower 100% elasticity index of the buffer cylinder 10 is advantageous for exhibiting a cushioning effect; for example, 7.5 N or less is desirable, and more desirably, even for a buffer cylinder with unfavorable conditions such as no change in inner diameter or wall elasticity at all and being straight, a buffering effect can be exhibited solely through uniform wall elasticity, with a 100% elasticity index of 6.5 N or less, and even more desirably, 2.5 or less.
Furthermore, a lower 60% elasticity index of the buffer cylinder 10 is advantageous for exerting a buffering effect, and a value of 4.6 N or less is desirable, and even in the case of a buffer cylinder with unfavorable conditions such as a straight one where the inner diameter and wall elasticity do not change at all, a value of 3.2 N or less is desirable in order to exert a buffering effect with uniform wall elasticity alone, and even more desirable is a value of 1.6 N or less.
However, in some cases where the cushioning function is provided in combination with other means, such as by providing an enlarged diameter portion, the desired cushioning function may be achieved even when the above-mentioned preferred ranges are exceeded.

In order to exert a cushioning function, the lower limit of the 30% elasticity index may be as close to 0 as possible.
It is also possible to use a guideline other than the 30% elasticity index, 60% elasticity index, and 100% elasticity index. For example, in the case of a buffer cylinder 10 that is a straight cylindrical tube of exactly the same inner diameter and has uniform wall elasticity, a lower 150% elasticity index is advantageous for exhibiting a buffer effect. For a buffer cylinder that is in the unfavorable condition of exhibiting a buffer effect solely through uniform wall elasticity, a value of 9.8 N or less is desirable, more preferably 8.4 N or less, and even more preferably 4.6 N or less.

<Length of buffer cylinder>
It is desirable for the buffer cylinder to have a certain length. In the present invention, the ratio R (=X/Φ) of the axial length X mm of the buffer cylinder to the inner diameter Φ of the blood inlet portion can be used as a guide. As can be seen from Figure 23 (described later) regarding a trumpet-shaped buffer cylinder, the axial length X of the buffer cylinder can be determined by considering cylindrical cut surfaces perpendicular to the axial direction at one end and the other end of the buffer cylinder and measuring the distance between these two planes. With a shape such as a trumpet-shaped buffer cylinder, X may be 0 mm.
R is preferably 1 or more, more preferably 1.2 or more, and even more preferably 1.5 or more.
However, in cases where the buffer cylinder 10 is highly elastic (easily stretchable) or has an enlarged diameter section, or in other cases where it is combined with other means for imparting a buffer function, it may be possible to achieve the desired buffer function even if R is less than 1.
The buffer cylinder does not necessarily have to be an exact cylinder. For example, if only a certain portion of the wall constituting the tubular blood flow path of the artificial blood vessel has a protruding, bulging shape toward the outside of the lumen, the entire tubular blood flow path including this protruding portion is considered to be a buffer cylinder. Furthermore, if there are multiple short buffer cylinders, the total length of the short buffer cylinders is considered to be the length of the buffer cylinder.

Other Embodiments
The present invention is not limited to the above-described first to seventh embodiments, nor is it limited to the examples described below.
For example, although each of the buffer system artificial blood vessels of the first to seventh embodiments includes the buffer cylinder 10 and the normal flow path section 20, it may not include the normal flow path section 20. That is, the entire buffer system artificial blood vessel (the entire section from the anastomosis with the artery to the anastomosis with the vein) may be formed of the buffer cylinder 10. In this case, too, the pressure and pulsatile changes in pressure, as well as the magnitude of the flow velocity and the change in flow velocity, of blood flowing in from the artery side can be reduced and then flow out to the venous side.
The buffer-type artificial blood vessels, which have the above-mentioned "physical buffering effect," also have the effect of remodeling the wall of the natural vein anastomosed downstream as a "biological buffering effect." In particular, microscopic findings (discussed below) are often clearly observed in a range of about 15 mm of the anastomosed natural vein wall closer to the artificial blood vessel.
However, the "biological buffering effect" can be more typically achieved by placing a buffer cylinder on the outside or inner lumen of the shunt vein wall, overlapping the vein wall, as described below. Therefore, the following explanation of the "biological buffering effect" will use an example of such an installation. By installing this buffer system blood vessel in this manner, its physical properties, such as elasticity, allow it to function as a buffer cylinder for the buffer system artificial blood vessel (physical buffering effect). At the same time, its physical properties, such as elasticity, induce the biological response of the overlying natural vein wall, remodeling the vein wall into a buffer system blood vessel (biological buffering effect). The combined effects of these two functions are expected to result in an even better buffer cylinder for the buffer system artificial blood vessel.

[Biological buffering effect]
So far, the action of the buffer system artificial blood vessel of the present invention has been described from the viewpoint of "physical buffer action." Next, the buffer action of the present invention will be described from the viewpoint of "biological buffer action."
The buffer system artificial blood vessel of the present invention, by virtue of its biological buffering effect, induces the formation of a gradient two-layer structure in the wall of the natural vein at the site of shunt creation: a smooth muscle layer that is richer in elastic fibers than the smooth muscle layer of a normal vein and thinner than the smooth muscle layer of a normal artery, and an outer collagen fiber layer that is rich in elastic fibers and thicker than the smooth muscle layer described above, thereby remodeling the vein at the site of shunt creation into a natural buffer system vessel (the "biological buffering effect of the buffer system artificial blood vessel"). In this way, the artificial blood vessel induces the remodeling of the natural vein at the site of shunt creation into a natural buffer system vessel having two layers: a smooth muscle layer rich in elastic fibers and a collagen fiber layer that is thicker than the smooth muscle layer and rich in elastic fibers. This induced natural buffer system vessel gradually buffers the highly pulsatile, high-velocity arterial hemodynamics at the arteriovenous anastomosis and the artificial blood vessel-venous anastomosis downstream, ultimately transitioning to venous hemodynamics, thereby enabling a low-pressure buffering effect. As a result, blood turbulence and pulsation changes in the venous wall are suppressed, and pathological changes such as intimal hyperplasia and thrombus formation can be prevented.

In connection with the above, the differences between buffer system vessels and normal arteries are explained in more detail below.
The walls of arteries and veins are composed of three layers: the tunica intima, tunica media, and tunica adventitia. Of these, the tunica intima contributes greatly to anticoagulation but has very little mechanical contribution. The arteries of the limbs used for hemodialysis shunt construction are typical muscular arteries, with two main mechanical components: the tunica media, which contains some elastic fibers and abundant smooth muscle, and the outer tunica adventitia, which is made up of elastic fibers, collagen fibers, etc.
Among these, the relatively small number of elastic fibers have a buffering function like a rubber tube, resisting and mitigating the high pulsatile blood pressure of the arteries due to their elasticity.
On the other hand, the smooth muscle layer, especially in normal muscular arteries, is particularly thick to minimize pulsating changes in the vascular wall against pulsating, high-pressure arterial hemodynamics, preventing turbulence and frictional stress fluctuations. Because this abundant smooth muscle is muscular, it has an active mechanical function, constricting the blood vessels while resisting arterial blood pressure, while also actively delivering high, pulsatile arterial blood pressure to the periphery without attenuating it. Due to the pressure-transfer function of this abundant smooth muscle in arteries, blood pressure remains almost constant in muscular arteries, from large aortas with internal diameters measured in centimeters to small arteries with internal diameters measured in fractions of a millimeter. In other words, normal arteries (composed of "smooth muscle > elastic fiber") do not have the function of buffering high, pulsatile arterial pressure due to the action of their abundant smooth muscle.
As described above, normal muscular arteries are composed of a very large amount of smooth muscle and relatively few elastic fibers (i.e., "smooth muscle > elastic fiber"), and are highly rigid against arterial hemodynamics.

On the other hand, veins have thin walls and lack the thick smooth muscle and elastic fiber layers found in arteries, resulting in low rigidity. Therefore, if an unusual blood flow situation were to occur in which arterial blood flows directly from an artery into a vein via an arteriovenous shunt, the vein would often have difficulty adapting to this condition, resulting in pathological biological reactions such as intimal thickening, as previously mentioned. To prevent this from happening through the actions of the vein itself at the site of shunt creation, the vein at the site of shunt creation must be remodeled into a low-pressure buffer system, capable of withstanding 100% pulsatile arterial pressure at the anastomosis site (i.e., the most upstream part of the vein), gradually attenuating and reducing blood pressure, pulsatility, and maximum flow velocity as it moves downstream, ultimately shifting to low-pressure venous hemodynamics with almost no pulsatility at the most downstream vein.

As mentioned above, normal arteries, such as the limb arteries used in shunts, are muscular arteries, composed of a very large amount of smooth muscle and relatively few elastic fibers (i.e., "smooth muscle > elastic fiber"), and are highly rigid against arterial hemodynamics.
On the other hand, when the native veins in the shunt area are remodeled into buffer vessels, the ratio of elastic fiber to smooth muscle is completely reversed from that of normal arteries, with a very abundant elastic fiber and a relatively thin smooth muscle layer ("elastic fiber > smooth muscle"). Therefore, in buffer vessels, the pressure delivery function of the smooth muscle layer is greatly reduced, while the pressure buffering function of the elastic fiber is extremely dominant. While maintaining the above-mentioned "elastic fiber > smooth muscle" configuration, i.e., maintaining the buffering function, buffer vessels have a characteristic morphology in which the entire native vascular wall gradually thins and transitions into a vein, i.e., gradually transitioning to a normal vein as the buffered pressure decreases (low-pressure buffer vessels).

On the other hand, arterial-like changes to the vein wall, such as those seen in conventional vascular banding methods using coatings to reinforce natural veins used as surgical implants, are arterialization (remodeling into an artery), not remodeling into a low-pressure buffer system. With conventional vascular banding, even if the arterialization of the vein gradually weakens and it naturally transitions downstream into a completely normal vein, this means that the vein gradually thins while retaining its "smooth muscle > elastic fiber" structure, and therefore this "arterialized" vein does not have a buffering function. As a result, the high pulsatile blood pressure and high-velocity blood flow caused by arterial hemodynamics affect the vein wall downstream of the shunt, resulting in pathological changes in the downstream vein. This is the clear functional difference between the gradual thinning of buffer system vessels and their transition into a normal vein, and the gradual thinning of normal arterial-like changes and their transition into a normal vein.

It is also worth noting that, in defining low-pressure buffering vessels, the morphological change of "elastic fiber > smooth muscle" described above is a necessary but not sufficient condition. In order to be able to define a vessel as a buffering vessel, in addition to this morphological characteristic, low-pressure buffering of hemodynamics through blood flow measurements must be proven by actual observation.

The inventors have discovered that this "biological buffering effect," i.e., the effect of remodeling the vein itself into a buffer system vessel, is more pronounced when a buffer system artificial vessel with appropriate blood flow buffering function is placed over the vein wall. Furthermore, as an application of this method, the buffer system artificial vessel of the present invention, which has the aforementioned "physical buffering effect" and is designed to have appropriate elasticity and shape to buffer hemodynamics, is placed over the vein wall and juxtaposed to the periphery of the vein wall as an external stent, or to the lumen side as an internal stent, or both. By placing these juxtaposed buffer system artificial vessels, the vein wall is remodeled into a low-pressure buffer system vessel within 1 to 4 weeks due to the action of the buffer system artificial vessel placed over the juxtaposed vein wall. As a result, the buffering function of the venous wall remodeled into a buffer system vessel, in addition to the buffering function of the previously placed buffer system artificial vessel, is also functioning, resulting in a more appropriate overall buffering function. If this layered, juxtaposed buffer system artificial blood vessel is made from a bioabsorbable material, the buffering function of the veins being remodeled into buffer system blood vessels will increase as the juxtaposed buffer system artificial blood vessel made from a bioabsorbable material gradually degrades and is absorbed, and after the juxtaposed buffer system artificial blood vessel is absorbed and disappears, the remaining natural veins will be able to independently exert a buffering effect as buffer system blood vessels.

As described above, the buffer system artificial blood vessel of the present invention may not only exhibit a buffer function by itself, but may also exhibit a buffer function in cooperation with other members or living tissues.
A simple method of making a cut in a shape such as a spiral is effective as a configuration advantageous for the above-mentioned "biological buffering effect." On the other hand, a linear cut is not so desirable because the vein wall in that area may change linearly, such as expanding or hardening.
The buffer system vascular prosthesis of the present invention includes a buffer system vascular prosthesis having such cuts.

Specifically, the buffer-system artificial blood vessel of the present invention includes a buffer cylinder that functions to buffer the dynamics of blood flowing from an artery to a vein, and has slits formed in it that allow the artificial blood vessel wall to separate. Examples of the shape of the slits include, but are not limited to, a spiral shape.

The buffer system artificial blood vessel with the above-mentioned cuts can be separated along the cuts, so it can be wrapped around the outside of the shunt vein wall and installed. This installation forms an artificial outer wall of the blood vessel as an external stent-like elastic body acting as an artificial blood vessel. As this outer wall overlaps with the inner vein, the natural vein wall itself is remodeled into a buffer system blood vessel (biological buffering effect). As a result, the wrapped outer wall and inner vein wall as a whole can be created as a buffer cylinder of a buffer system artificial blood vessel.

The above-mentioned buffer system artificial blood vessel can also be placed inside the blood vessel lumen at the shunt site and its drainage area. This placement forms the innermost wall of the artificial blood vessel as an internal stent-like elastic body. This innermost wall overlaps the outer blood vessel wall, remodeling the natural vein wall itself into a buffer system blood vessel (biological buffering action). As a result, the entire buffer system artificial blood vessel, with its outer wall and inner slits, can function as a buffer cylinder for the buffer system artificial blood vessel. While buffer system artificial blood vessels placed inside the lumen can be either slit or not, the slits allow them to be deformed into a long, thin shape, making them easy to insert into the blood vessel lumen and easily restore to the appropriate outer diameter within the lumen.

In the above, it is preferable that the buffer cylinder with the cuts formed in the buffer system artificial blood vessel satisfy at least one of the following conditions at least in part: 30% elasticity index of 3.1 N or less, 60% elasticity index of 4.2 N or less, 100% elasticity index of 6.2 N or less, and 150% elasticity index of 8.9 N or less.

Like other buffer cylinders, the buffer cylinder with cuts can be made entirely or partially from, for example, a bioabsorbable material or metal, although this is not a specific material.

Examples and comparative examples of the buffer-type artificial blood vessel according to the present invention are given below, but the present invention is not limited to these examples.
13 to 28 are shown as reference figures for the following examples and comparative examples, but these are conceptual diagrams of the shapes and are not necessarily the actual measured shapes. In each figure, the symbols T and K represent the normal path section and the buffer cylinder, respectively.
In the following, the 30% elastic index, 60% elastic index, 100% elastic index and 150% elastic index are values measured by the above-mentioned measurement method, and the load measurements were carried out using the following measuring instruments.
Load measuring device: Desktop load measuring device MODEL-1356R (AIKOH ENGINEERING)
Force gauge: MODEL-RX-10 (AIKOH ENGINEERING)
Hardware: Powerlab 2/26 (AD Instrument)
Software: Labchart (AD Instrument)
Furthermore, Examples 1 to 24 are presented mainly from the viewpoint of "physical buffering action," while Examples 25 and onward are presented mainly from the viewpoint of "biological buffering action."

Example 1
A buffer-type artificial blood vessel having the shape shown in FIG. 13 was fabricated by the following procedure.
Monofilament polyurethane fibers were wound cylindrically around a rotating iron core with an outer diameter of 6 mm. During this process, the traverse of the iron core was adjusted so that more fibers were wound on one side and less on the other side. A heat-welding process was then performed to produce a polyurethane tube with an inner diameter of 6 mm. A 60 mm long section of this tube was cut out to serve as a buffer cylinder with the thicker end facing upstream.
A 14 cm long section with an inner diameter of 6 mm was cut from the center of a conventional commercially available artificial blood vessel (Distaflo®, manufactured by C.R. Bard, Inc., with support), and the upstream end of the buffer cylinder was anastomosed to this section with adhesive. This was used in the experiment as a buffer-type artificial blood vessel with a buffer cylinder.

Example 2
A buffer-type artificial blood vessel having the shape shown in FIG. 14 was fabricated by the following procedure.
A PTFE tube in a trumpet shape (Fig. 14) was produced by the hot coining method. After annealing, the tube was 60 mm long and had a circular inner diameter, with an inner diameter of 6 mm at one end and an inner diameter of 8 to 10 mm at the other end. Of these, the tube with an inner diameter of 8 mm at the other end was used in Example 2. This tube was used as a buffer cylinder with the end with an inner diameter of 6 mm as the upstream end, and a buffer-type artificial blood vessel with a buffer cylinder was obtained in the same manner as in Example 1.

Example 3
A buffer-type artificial blood vessel having the shape shown in FIG. 15 was fabricated by the following procedure.
A 6 mm outer diameter aluminum tube was deformed to create a core mold. One end of the core mold remained circular, but the cross-sectional shape gradually changed from a 6 mm diameter circular shape to a rectangular shape approaching an oval shape toward the other end. A mesh woven with polyurethane and nylon support threads was wrapped around the core mold, and silicone rubber was applied over the mesh. The silicone rubber wall thickness was uniform around the entire circumference at the circular cross-section end, but varied around the entire circumference at the other end, with the thickness reduced toward the minor axis end of the oval cross-section. A 60 mm length of this tube was cut into a buffer cylinder, with the circular end serving as the upstream end. A buffer-system artificial blood vessel with a buffer cylinder was obtained, similar to Example 1. The cross-sectional shape of this buffer cylinder changed from an oval (lower right of Figure 15 ) to a circle (upper right of Figure 15 ) in response to changes in internal arterial blood pressure.
The combination of two types of fibers with different elastic properties that make up this support thread is as follows: polyurethane monofilament is soft and highly extensible, while the nylon thread wrapped around it has poor elasticity. Therefore, even if the polyurethane monofilament stretches due to blood pressure, if the stretch is small, there is slack in the area where the nylon thread is wrapped, allowing the polyurethane thread to stretch freely and expand the artificial blood vessel. However, if a higher blood pressure is applied, the polyurethane stretches even more, causing the lumen of the artificial blood vessel to attempt further expansion, the slack in the area where the nylon thread is wrapped reaches its limit, applying tension to the nylon thread and restricting the elongation of the polyurethane thread. In this way, by supporting the extensible thread with a less extensible thread, the limit of elongation can be adjusted. This effect allows the buffer cylinder to expand easily up to a certain blood pressure, providing a significant buffering effect, but above that blood pressure, the expansion of the buffer cylinder is restricted, regulating excessive expansion of the buffer cylinder and ultimately providing an appropriate buffering effect.

Example 4
A buffer-type artificial blood vessel having the shape shown in FIG. 16 was fabricated by the following procedure.
A 60 mm long PTFE tube, as shown in Figure 16, was fabricated using the hot coining method. After annealing, one end was circular with an inner diameter of 6 mm (circumference approximately 18.8 mm), and the other end had a rectangular cross-sectional shape with a rounded shape close to an oval, with a circumference of 25 to 40 mm. In Example 4, one of these tubes with a circumference of 25 mm at the other end was used. The PTFE wall had a uniform thickness around the entire circumference of the circular cross-section. Using this tube as a buffer cylinder with the circular cross-sectional shape of 6 mm inner diameter as the upstream side, a buffer-type artificial blood vessel with a buffer cylinder was obtained in the same manner as in Example 1.

Example 5
A buffer-type artificial blood vessel having the shape shown in FIG. 17 was fabricated by the following procedure.
A 6 mm inner diameter silicone rubber tube was placed over a 6 mm outer diameter iron core, and reinforced by spirally wrapping 0.8 mm thick polypropylene monofilament thread at a pitch of 6 mm from the outside. A 60 mm long piece of the tube was cut out as a buffer cylinder, and a buffer-type artificial blood vessel with a buffer cylinder was obtained in the same manner as in Example 1. This buffer cylinder moves in a spiral shape in response to changes in the internal arterial pressure.

Example 6
A buffer-type artificial blood vessel having the shape shown in FIG. 18 was fabricated by the following procedure.
PTFE tubes with a length of 60 mm, as shown in Figure 18, were fabricated using the hot coining method. After annealing, one end was circular with an inner diameter of 6 mm (circumference approximately 18.8 mm), and the other end had a rectangular cross-sectional shape with a rounded shape close to an oval, with circumferences ranging from 25 mm to 40 mm. For Example 6, the tube with a 25 mm circumference was used. The PTFE wall thickness gradually decreased from the circular cross-sectional end to the other end. In the cross-section perpendicular to the axial direction, the wall thickness varied along the circumference, with the minor axis end of the oval being thinner. The end with the circular cross-sectional shape of this tube was used as the upstream side, and a buffer-system artificial blood vessel with a buffer cylinder was obtained, as in Example 1. The cross-sectional shape of this buffer cylinder changed from oval to circular due to changes in the internal pressure of arterial blood.

Example 7
A buffer-type artificial blood vessel having the shape shown in FIG. 19 was fabricated by the following procedure.
A monofilament polyurethane thread was wound cylindrically around a rotating iron core with an outer diameter of 6 mm while sprinkling salt granule spacers on the surface. During this process, the traverse of the iron core was adjusted so that more fibers were wound around both ends of the core and fewer fibers were wound around the center. A larger amount of salt granules was sprinkled in the center, creating a highly porous, highly porous central region. The spacers were washed away in running water, followed by a fusion process to produce a polyurethane tube with an inner diameter of 6 mm. A 60 mm-long section was cut from the center of this tube, and the thick-walled end was used as the upstream end to form a buffer cylinder. Similar to Example 1, a buffer-type artificial blood vessel with a buffer cylinder was obtained. The cross-sectional shape of this buffer cylinder, the thin-walled central region, expanded and deformed due to changes in the internal pressure of arterial blood.
The function of the thick-walled downstream portion of the buffer cylinder in this embodiment will be briefly explained below. The wall of the buffer cylinder's central portion is thinner, so it acts as a "buffer basin" that expands with the inflow of arterial blood flow and provides a buffering function. The downstream portion is also elastic because it is made of polyurethane, a highly elastic material, but its wall is thicker than the central portion of the buffer cylinder, so it is less elastic than the central portion. Therefore, this thick-walled downstream portion acts as a relatively flexible "exit gate" of the buffer basin, further enhancing the buffering effect of the buffer basin.

Example 8
A buffer-type artificial blood vessel having the shape shown in FIG. 20 was fabricated by the following procedure.
An 8 mm outer diameter aluminum rod was machined to create two 2 mm deep grooves on opposing 180° spirals with a 16 mm pitch, rotating in the same direction. While rotating the aluminum rod with the two unidirectional spiral grooves, a monofilament polyester thread was wrapped around it in a cylindrical shape. During this process, an anticoagulant-containing glue was sprayed onto the polyester tube to bond the threads together, and a 1 mm thick aluminum wire was then wrapped around the grooves to compress them. This process was repeated twice to form helical pleats in the tube. The tube was then cut into 60 mm lengths to form a buffer cylinder. Similar to Example 1, a buffer-type artificial blood vessel with a buffer cylinder was obtained. The inner diameter of this buffer cylinder fluctuates in a spiral pattern due to changes in internal arterial pressure.

Example 9
A buffer-type artificial blood vessel having the shape shown in FIG. 21 was fabricated by the following procedure.
Silicone rubber was applied in layers around an iron core with an outer diameter of 6 mm to obtain a cylindrical multilayer structure consisting of approximately four layers, each layer offset from the others. During this process, the rubber layers were adjusted to form uniform thicknesses along the entire axial direction of the cylinder. A 60 mm long tube was cut from this 6 mm inner diameter, uniform wall-thick silicone rubber tube to form a buffer cylinder. Similar to Example 1, a buffer-type artificial blood vessel with a buffer cylinder offset from the layers was obtained.
In this buffer artificial blood vessel, the layers are displaced relative to one another, and the layers are displaced by pulse pressure, providing a buffer effect.

Example 10
A buffer-type artificial blood vessel having the shape shown in FIG. 22 was fabricated by the following procedure.
A cylindrical body having an inner diameter of 5 mm was obtained by knitting woolly nylon fibers using the whole garment method.
This cylindrical body was cut into a length of 50 mm and placed twice on an iron core with an outer diameter of 6 mm. One end of this double layer was then covered with another piece of the cylindrical body cut into a length of 20 mm, so that the 20 mm portion from the one end was a triple layer and the remaining 30 mm was a double layer.
The mesh of the thus obtained cylindrical mesh fabric, 50 mm long and having one end triple-layered and the other double-layered, was treated with an anticoagulant-containing glue to smooth out the stitches, yielding a layered structure. This was used as a buffer cylinder, with the triple-layered end of the wall as the upstream end, to obtain a buffer-type artificial blood vessel with a buffer cylinder, as in Example 1. The layered layers can shift due to pulse pressure, enhancing the buffering effect.
Furthermore, after the internal diameter of the buffer cylinder expanded to 130% in 100 seconds, the internal diameter returned to 125% or less within 200 seconds when the external force was removed.
Furthermore, the buffer cylinder is knitted using the whole garment method, a weft knitting technique that can seamlessly knit even complex shapes based on a small diameter cylinder of millimeters, so it is required to have the mobility to expand and contract in the radial direction, and the inner diameter and wall shape can change.
For comparison, a comparative buffer cylinder was prepared in the same manner except that non-woolly processed nylon fibers were used. After the inner diameter of the comparative buffer cylinder expanded to 130% in 100 seconds, the inner diameter did not return to 125% or less within 200 seconds after the external force was removed.

Example 11
A buffer-type artificial blood vessel having the shape shown in FIG. 17 was fabricated by the following procedure.
A 6 mm inner diameter polyurethane tube was placed over a 6 mm outer diameter iron core, and a 1.1 mm thick silicone rubber monofilament thread was wound spirally from the outside at a pitch of 6 mm and adhesively fixed to reinforce the tube. A 60 mm long piece of the tube was cut out as a buffer cylinder, and a buffer-type artificial blood vessel with a buffer cylinder was obtained in the same manner as in Example 1. The expansion section of this tube fluctuates spirally in response to changes in the internal arterial pressure.

Example 12
A buffer-type artificial blood vessel having the shape shown in FIG. 24 was fabricated by the following procedure.
Using the hot coining method, a PTFE trumpet-shaped tube was fabricated. The inner diameter was 6 mm at one end after annealing, and the wall thickness gradually decreased toward the other end as shown in Figure 23. This trumpet-shaped tube did not exhibit the wall thickness change in the lateral direction of the cross section perpendicular to the axial direction (in Example 6, the minor axis direction of the oval cross section) thinner than the wall thickness along the major axis, as in Example 6. This trumpet-shaped tube was cut as shown in Figure 24, and a buffer-type artificial blood vessel with a buffer cylinder was obtained, similar to Example 1, with the smaller diameter end serving as the upstream buffer cylinder. In Example 12, the distance X was set to 1.6, i.e., X÷Φ=R, i.e., X=9.6 mm.

Example 13
A trumpet-shaped tube prepared in the same manner as in Example 12 was cut as shown in Figure 24, with the end with the smaller diameter on the upstream side as a buffer cylinder, to obtain a buffer-type artificial blood vessel with a buffer cylinder in the same manner as in Example 1. In Example 13, the distance X was set to X÷Φ=R=1.5, i.e., X=9 mm.

Example 14
A trumpet-shaped tube similar to that shown in Figure 23 was prepared by applying silicone rubber to the periphery of a trumpet-shaped core mold having the same shape as the lumen in Figure 23. In this case, the thickness of the silicone rubber toward the opening side of the trumpet was gradually tapered as shown in Figure 23. This trumpet-shaped tube was cut as shown in Figure 24, and the end with the smaller diameter was used as the upstream buffer cylinder, to obtain a buffer-type artificial blood vessel with a buffer cylinder as in Example 1. In the case of Example 14, the distance X was set to X÷Φ=R=1, i.e., X=6 mm.

Example 15
A trumpet-shaped tube was prepared by winding polyurethane monofilament around a trumpet-shaped core mold similar to the lumen shown in Figure 23. The thickness of the polyurethane monofilament wound on the open side of the trumpet was gradually reduced as shown in Figure 23. After the welding process, this trumpet-shaped tube was cut as shown in Figure 25, and the end with the smaller diameter of the stump was used as the upstream buffer cylinder, to obtain a buffer-type artificial blood vessel with a buffer cylinder, as in Example 1. In Example 15, the distance X was set to 0 (X÷Φ=R), i.e., X=0 mm.

Example 16
Using the hot coining method, a PTFE trumpet-shaped cylinder was produced, with an inner diameter of 6 mm at one end after annealing, and the inner diameter widening toward the other end as shown in Figure 18, with the wall thickness of the oval minor axis of the trumpet-shaped tube gradually becoming thinner than that of the major axis of the oval. This trumpet-shaped tube was cut as shown in Figure 24, with the smaller-diameter end serving as the upstream buffer cylinder, to obtain a buffer-type artificial blood vessel with a buffer cylinder, as in Example 1. In Example 16, the distance X was set to X÷Φ=R=1.2, i.e., X=7.2 mm.

Example 17
A PTFE trumpet-shaped tube was prepared in the same manner as in Example 16. This trumpet-shaped tube was cut as shown in Figure 24, and the end with the smaller diameter was used as the upstream buffer cylinder, to obtain a buffer-type artificial blood vessel with a buffer cylinder in the same manner as in Example 1. In Example 17, the distance X was set to X÷Φ=R=1, i.e., X=6 mm.

Example 18
A PTFE trumpet-shaped tube was prepared in the same manner as in Example 16. This trumpet-shaped tube was cut as shown in Figure 25, and the end with the smaller diameter of the stump was used as the upstream buffer cylinder, to obtain a buffer-type artificial blood vessel with a buffer cylinder in the same manner as in Example 1. In Example 18, the distance X was set to X÷Φ=R=0, i.e., X=0 mm.

Example 19
A mesh with a length of 60 mm, which was knitted using support yarn made of polyurethane monofilament wrapped with ultra-fine Tetron yarn, was wrapped around an aluminum tube with an outer diameter of 6 mm.
Next, a 30 mm long mesh was wrapped around one end of the mesh wrapped around the aluminum tube, and then a 15 mm long mesh was wrapped twice around one end of the double-layered layered mesh section, creating a single layer for the downstream 30 mm long section, a double layer for the central 15 mm long section, and a quadruple layer for the most upstream 15 mm long section. The stumps of the mesh were heat-fixed. Alginic acid was sprayed onto the 6 mm inner diameter tube with the multilayered structure thus created and cross-linked with calcium to create a buffer cylinder with the quadruple-layered end as the upstream end. A buffer-system artificial blood vessel with this buffer cylinder was fabricated in the same manner as in Example 1, resulting in Example 19. The layers of the multilayered structure shift relative to each other due to pulse pressure, enhancing the buffering effect.

Example 20
A mesh knitted using support threads consisting of polyurethane monofilaments wrapped with ultrafine Tetron yarn was wrapped around an aluminum tube with an outer diameter of 6 mm. Unlike Example 19, the mesh was wrapped evenly in two layers over its entire length. The stumps of the mesh were heat-fixed. Alginic acid was sprayed onto the tube with an inner diameter of 6 mm thus prepared, followed by cross-linking and fixation with calcium, and then cut into a length of 60 mm to prepare a buffer cylinder. A buffer-system artificial blood vessel with this buffer cylinder was prepared in the same manner as in Example 1, and designated Example 20.

Example 21
A cylindrical body having an inner diameter of 8 mm and made of woolly processed polyester yarn was placed on an aluminum tube having an outer diameter of 6 mm, and then contracted in the axial direction of the aluminum tube to form a bellows-shaped cylindrical body.
This bellows-shaped cylinder was placed over an aluminum tube and then treated with alginic acid and cross-linked with calcium. The bellows-shaped cylinder, which had been cross-linked and maintained in its bellows shape, was cut into a length of 60 mm to obtain a buffer cylinder. A buffer-type artificial blood vessel having this buffer cylinder was then fabricated in the same manner as in Example 1, and designated Example 21. Because this buffer cylinder has a bellows shape, it expands and contracts in response to pulse pressure, thereby enhancing the buffering effect.

Example 22
Polyurethane thread was uniformly wrapped around the surface of an aluminum tube with an outer diameter of 6 mm and fixed by heating. This tube was cut into a length of 60 mm to form a buffer cylinder. A buffer-type artificial blood vessel having this buffer cylinder was fabricated in the same manner as in Example 1, and this was designated Example 22.

Example 23
Silicone rubber (KE-4896, Shin-Etsu Chemical Co., Ltd.) was evenly applied to a core of an aluminum tube with an outer diameter of 6 mm. This tube was cut into a length of 60 mm to form a buffer cylinder. A buffer-type artificial blood vessel having this buffer cylinder was fabricated in the same manner as in Example 1, and this was designated Example 23.

Example 24
Resin clay was applied to the entire periphery of the central portion of an aluminum tube with an outer diameter of 6 mm, creating a 50 mm long section with an outer diameter of 8 mm. Liquid molding urethane resin (Gummy Cast Zero, Nissin Resin Co., Ltd.) was then uniformly applied to the entire aluminum tube. Immediately afterwards, while the urethane was still liquid, a polypropylene monofilament reinforcement material was wrapped around the entire length at a pitch of 20 mm per circumference. Further molding urethane resin was applied uniformly on top of this to embed the previously wrapped polypropylene monofilament. After the urethane resin hardened into a gummy state, the aluminum tube and resin clay were removed to create a tube reinforced with polypropylene monofilament, with a 50 mm long central portion having an inner diameter of 8 mm and two end portions with an inner diameter of 6 mm. A 60 mm long section consisting of a central portion with an inner diameter of 8 mm and a length of 50 mm and two end portions with lengths of 5 mm and an inner diameter of 6 mm connected to the central portion was cut out from this tube, resulting in a 60 mm long reinforced tube. This tube was used as a buffer cylinder, and a buffer-type artificial blood vessel having a buffer cylinder was obtained in the same manner as in Example 1.
The wrapped polypropylene monofilament is a relatively inelastic material, gradually thickening from 0.2 mm to 1.0 mm and then gradually tapering back to 0.2 mm over a 20 mm interval. As a result, the very soft and stretchable polyurethane wall expands outward in response to arterial hemodynamics, expanding the lumen. Meanwhile, the polypropylene spiral reinforcement, i.e., the spiral valve-like portion, resists lumen expansion. The interaction between these two components causes the vessel wall to expand into a spiral lumen, enhancing the buffering effect. Because the height of the spiral valves varies depending on the thickness of the polypropylene, the valve-like spiral structure protruding into the lumen forms a spiral valve consisting of a series of crescent-shaped valves, with small protrusions in the thin reinforcement areas and large protrusions in the thick reinforcement areas. At the same time, the polypropylene reinforcement effectively prevents the soft urethane wall of the buffer cylinder from becoming constricted or blocked by twisting or external pressure.

Example 25
Four layers of No. 1 bioabsorbable suture thread (Lacron®, purchased from Kono Seisakusho, Ichikawa City, Japan) made from a copolymer of 75% lactic acid and 25% caprolactam (hereinafter sometimes referred to as LA/CL) were prepared and wound around an aluminum tube with an outer diameter of 6 mm and a length of 60 mm, with the double strands alternately overlapping in opposite directions. At one end of the aluminum tube, the threads were wound closely together, with adjacent strands touching each other. The spacing between the strands was gradually increased until the spacing at the opposite end was 2.5 mm. The helical shape of the LA/CL suture was stabilized by heat treatment, and this 60 mm long, 6 mm inner diameter, double-stranded, reverse-stranded section was fabricated as a buffer artificial blood vessel for placement in a vein. In animal experiments, a 14-cm section with a 6 mm inner diameter was cut from the center of a conventional artificial blood vessel, similar to that used in other examples. This artificial blood vessel was used to create a conventional artificial blood vessel shunt between the external jugular vein and the common carotid artery. The shunt artificial blood vessel was wrapped around the venous wall, anastomosed to the artificial blood vessel, at a distance of 60 mm downstream from the anastomosis, overlapping the venous wall. The dense end of the spiral LA/CL suture was placed on the artificial blood vessel side, i.e., upstream of the blood flow, and the sparse end of the spiral LA/CL suture was placed on the opposite side, i.e., downstream of the blood flow, creating a 60 mm reverse-direction double-helix buffer artificial blood vessel. A glue (hereinafter sometimes referred to as LA/CL glue) prepared by dissolving LA/CL in 1,3-dioxolane at a concentration of 100 mg/ml was used to glue and fix the intersection of the two reverse-direction spiral LA/CL sutures. This buffer artificial blood vessel functions as a cylindrical buffer blood vessel hybridized with the vein wall.

Example 26
A bioabsorbable medical nonwoven fabric (Neoveil®, R015G type, purchased from Gunze Co., Ltd., Osaka City) was coated with calcium phosphate slurry and cut into a 20 mm wide spiral tape. This tape was then spirally wrapped around an aluminum tube with an outer diameter of 6 mm and a length of 60 mm. The tape was then completely overlapped at one end of the aluminum tube, gradually reducing the overlap until it was doubled at the other end. The upstream portion of the tape was heat-treated more intensely to stabilize the spiral shape. This 60 mm long, 6 mm inner diameter spiral was fabricated as a buffer artificial blood vessel for juxtaposition to a vein.
In animal experiments, a 14-cm section with an inner diameter of 6 mm was cut from the center of a conventional artificial blood vessel similar to that used in other examples. This artificial blood vessel was used to create an arteriovenous shunt between the external jugular vein and the common carotid artery. A spiral tape-shaped buffer artificial blood vessel was wrapped around the venous wall, overlapping it, at a location 60 mm downstream from the anastomosis, on the outside of the venous wall anastomosed to the artificial blood vessel of the shunt. The four-fold overlapping end of the spiral tape was positioned on the artificial blood vessel side, i.e., upstream of the blood flow, and the single-fold overlapping end was positioned on the opposite side, i.e., downstream of the blood flow, to create a 60-mm spiral buffer artificial blood vessel.
Finally, the spiral tape was adjusted to ensure the desired shunt blood flow was achieved using an ultrasonic hemometer, and a 20 mg/ml aqueous solution of sodium alginate (Snow Algin L, purchased from Fuji Chemical Industry Co., Ltd., Wakayama City) was sprayed evenly to maintain this state. The reason for spraying evenly was to adjust the cross-linking of alginic acid so that it would be stronger in the upstream area due to the abundant calcium phosphate, and weaker in the downstream area due to the lack of calcium phosphate.
This buffer cylinder functions as a cylindrical buffer vessel hybrid with the venous wall.

Example 27
Two types of sodium alginate aqueous solutions were prepared as materials for the buffer cylinder. Namely, Snow Algin M was used as high-viscosity sodium alginate, and Snow Algin SL was used as low-viscosity sodium alginate (both manufactured by Fuji Chemical Industry Co., Ltd.), each prepared as an aqueous solution with a concentration of 20 mg/ml. Furthermore, a 20-fold diluted solution of calcium gluconate (Calcicol, manufactured by Nichi-Iko Pharmaceutical Co., Ltd.) was prepared as a cross-linking agent.
In animal experiments, a 14-cm section with an inner diameter of 6 mm was cut from the center of a conventional artificial blood vessel similar to that used in other examples. This artificial blood vessel was used to create an arteriovenous shunt between the external jugular vein and the common carotid artery. The sodium alginate and calcium gluconate aqueous solutions were simultaneously sprayed in three or more separate doses around the venous wall at a distance of 60 mm downstream from the anastomosis of the shunt with the conventional artificial blood vessel. The high-viscosity sodium alginate solution was sprayed in large amounts on the side closest to the conventional artificial blood vessel (upstream side), and the low-viscosity sodium alginate solution was sprayed in large amounts on the opposite side (downstream side). During the separate sprayings, the desired blood flow was monitored using an ultrasonic blood flowmeter, and the administration of alginic acid and calcium gluconate was adjusted to maintain the desired blood flow.
This buffer cylinder functions as a cylindrical buffer vessel hybrid with the venous wall.

Example 28
A commercially available artificial blood vessel (Dacron® artificial blood vessel (Japan Lifeline Co., Ltd., J-Graft, Shield Neo S) with an inner diameter of 7 mm, a conventional artificial blood vessel made of polyester, was cut to a length of 60 mm and a first spiral tape was created by making a spiral cut using a hot scalpel. The spiral pitch was 5 mm. Next, a similar spiral tape was made with the spiral direction reversed (second spiral tape). The edges of the spiral cuts were curved outward, and the cut ends were rounded with silicone rubber (KE-4896, Shin-Etsu Chemical Co., Ltd.). These spiral tapes were tightly wrapped around aluminum tubes with an inner diameter of 6 mm and heat-treated to stabilize the shape.
In animal experiments, a 14-cm length of a 6 mm inner diameter section was cut from the center of a conventional artificial blood vessel, similar to that used in other examples. This artificial blood vessel was used to create an arteriovenous shunt between the external jugular vein and the common carotid artery. A first spiral tape was wrapped around the venous wall, 60 mm downstream from the anastomosis, on the outside of the shunt artificial blood vessel. The downstream end of the conventional artificial blood vessel overlapped the upstream end of the spiral tape by 5 mm. A second spiral tape, wound in the opposite direction, was similarly wrapped around the first spiral tape. Finally, the two spiral tapes were stacked to form a 60 mm buffer cylinder. The overlap between the upstream end of the spiral tape and the downstream end of the conventional artificial blood vessel was secured with a hook-and-loop fastener. Finally, the desired blood flow condition was confirmed using an ultrasonic blood flowmeter, and the wrapping of the two spiral tapes and the hook-and-loop fastener were adjusted to maintain the desired condition.
This buffer cylinder functions as a cylindrical buffer vessel hybrid with the venous wall.

Example 29
A commercially available artificial blood vessel graft (Distaflo®, C.R. Bard, Inc., with support), a conventional artificial blood vessel made of ePTFE, was used, and a straight central section with an inner diameter of 6 mm was cut to a length of 65 mm to create a spiral tape similar to that of Example 28. However, the pitch of the spiral shape gradually decreased from 5 mm at the long end to 2.5 mm at the short end. To stabilize the shape and protect the surrounding tissue, the cut end was rounded with silicone rubber (KE-4896).
In the animal experiment, a 14-cm section with an inner diameter of 6 mm was cut from the center of a conventional artificial blood vessel, the same as in the other examples. This artificial blood vessel was used to create an arteriovenous shunt between the external jugular vein and the common carotid artery. A spiral tape was wrapped around the venous wall, 60 mm downstream from the anastomosis, on the outside of the shunt artificial blood vessel. The end of the spiral tape with the shorter pitch was positioned on the conventional artificial blood vessel side, i.e., upstream of the blood flow, and the end with the longer pitch was positioned on the opposite side, i.e., downstream of the blood flow. The downstream end of the conventional artificial blood vessel and the upstream end of the spiral tape overlapped by 5 mm. Finally, the desired blood flow state was confirmed using an ultrasonic blood flowmeter, and the wrapping of the spiral tape was adjusted so that the desired state could be maintained. To maintain this wrapping state, the walls of the spiral tape were glued together with 100 mg/ml LA/CL glue at four locations, spaced 20 mm apart from the most upstream portion, in the order of 12 o'clock, 4 o'clock, 8 o'clock, and 12 o'clock on the circumference of the pitch. In addition, the overlapping portion between the downstream end of the conventional artificial blood vessel and the upstream end of the spiral tape was glued together with LA/CL glue around the entire circumference.
This buffer artificial blood vessel functions as a cylindrical buffer blood vessel by hybridizing with the vein wall.
Furthermore, by using a biodegradable material such as LA/CL glue, the LA/CL glue prevents the spiral tape from gradually loosening due to blood pressure, and during this time the LA/CL glue gradually decomposes while the biological buffering action matures.As a result, the physical buffering action is gradually replaced by the biological buffering action, and it is expected that the self-regulating function of the overall buffering action will become more advanced.

Example 30
A 0.098 mm diameter stainless steel spring wire (SUS304, NAS304-0.1, purchased from Seiwa Steel Wire Co., Ltd., Osaka City) was bent into a shape with 11 zigzag reverse 180-degree bends every 35 mm. The bends were alternating between U-shaped 180-degree bends, V-shaped 180-degree bends, and U-shaped 180-degree bends, resulting in six U-shaped bends sandwiched between V-shaped bends. This zigzag iron wire was wrapped around an iron core with an outer diameter of 5 mm, with the U-shaped bends aligned in one direction and the V-shaped bends aligned in the opposite direction. The shape was stabilized by heat treatment, and silicone rubber (KE-4896) was applied to the surface of the wire. A 35 mm long, 6 mm inner diameter tube was obtained from the zigzag spring iron wire. The tube, made of spring-shaped iron wire coated with silicone rubber, was covered with a porous membrane of ethylene-vinyl alcohol copolymer, and was created as a buffer cylinder to be placed in layers alongside the lumen of the vein.
In animal experiments, a 14-cm section with an inner diameter of 6 mm was cut from the center of a conventional artificial blood vessel, the same as in other examples. This conventional artificial blood vessel was used to create an arteriovenous shunt between the external jugular vein and the common carotid artery. Specifically, the shunt was placed as a buffer cylinder on the lumen side of the vein wall, 35 mm downstream from the downstream end of the conventional artificial blood vessel. A 5-mm section of the tube near the V-shaped bend was placed on the lumen side of the wall at the downstream end of the conventional artificial blood vessel and secured to the downstream end of the conventional artificial blood vessel by the elasticity of a spring. A 30-mm section of the tube near the U-shaped bend, on the opposite end, was placed on the downstream side of the vein wall, gently expanding the vein wall with the elasticity of the spring. After placement, Bayer aspirin-based anticoagulation therapy was administered.
This buffer cylinder hybridizes with the vein wall and functions as a cylindrical buffer vessel.

Example 31
A coil spring was prepared by winding a 0.02 mm diameter stainless steel spring wire (SUS304, 751107), thinner than that used in Example 30, around a 60 mm long iron core, which gradually transitioned from an oval with an average outer diameter of 6 mm (minor diameter 4 mm × major diameter 8 mm) to a perfect circle with an outer diameter of 7 mm. The steel wire was wound in an oval shape on the 6 mm diameter side, with the end of the first winding touching the beginning of the winding, and then in a circular spiral with a gradually increasing spiral pitch until the opposite end, with a 7 mm diameter, had a 10 mm pitch. To prevent the tip of the steel wire on the 10 mm pitch side from contacting the vein wall, the end of the wire was curled into a 2 mm diameter spiral. The shape was stabilized by heat treatment, and a silicone rubber (KE-4896) was applied to the wire surface to prepare a 60 mm long spiral tube.
In the animal experiment, unlike Example 30, a buffer artificial blood vessel was placed on the lumen side of the venous wall at a location 60 mm downstream from the upstream end of the venous anastomosis of the autologous blood vessel of an arteriovenous shunt that did not use a conventional artificial blood vessel, with the 6 mm diameter side facing upstream. After placement, anticoagulant therapy using mainly Bayer aspirin was administered.
This buffer cylinder hybridizes with the vein wall and functions as a cylindrical buffer vessel.

Comparative Example 1
A commercially available conventional artificial blood vessel (Venaflo (registered trademark), manufactured by C.R. Bard, Inc., inner diameter 6 mm, unsupported) was used, and a central portion with an inner diameter of 6 mm was cut out to a length of 20 cm to be used as the artificial blood vessel of Comparative Example 1.
The shape is a right cylinder as shown in FIG.

Comparative Example 2
A 20 cm length of a central portion with an inner diameter of 6 mm from a conventional commercially available artificial blood vessel (Distaflo (registered trademark), manufactured by C.R. Bard, Inc., with support) was cut out and used as the artificial blood vessel of Comparative Example 2.
The shape is a reinforced right cylinder as shown in FIG.

Comparative Example 3
As in Example 12, a PTFE trumpet-shaped tube was fabricated by the hot coining method, with the trumpet-shaped wall gradually thinning as shown in Figure 23. This trumpet-shaped tube was cut as shown in Figure 24 to fabricate a buffer cylinder with the smaller diameter end on the upstream side of the buffer cylinder. For Comparative Example 3, the distance X was set to 1.2 (X÷Φ=R), i.e., X=7.2 mm. The upstream end of this buffer cylinder was adhesively fixed to a central portion of a commercially available conventional artificial blood vessel (Distaflo®, manufactured by C.R. Bard, Inc., with support) with an inner diameter of 6 mm. The conventional artificial blood vessel was then cut at a point within the buffer cylinder where the total length of the circumferential cylindrical portion and the conventional artificial blood vessel was 20 cm. This 20 cm portion was used as the artificial blood vessel of Comparative Example 3.

Comparative Example 4
As in Comparative Example 3, a PTFE trumpet-shaped tube was fabricated by the hot coining method, with the trumpet-shaped wall gradually thinning as shown in Figure 23. This trumpet-shaped tube was cut as shown in Figure 24 to fabricate a buffer cylinder with the smaller diameter end on the upstream side of the buffer cylinder. In Comparative Example 4, the distance X was set to 1 (X÷Φ=R), i.e., X = 6 mm. The upstream end of this buffer cylinder was adhesively fixed to a central portion of a commercially available conventional artificial blood vessel (Distaflo®, manufactured by C.R. Bard, Inc., with support) with an inner diameter of 6 mm. The conventional artificial blood vessel was then cut at a point within the buffer cylinder where the total length of the circumferential cylindrical portion and the conventional artificial blood vessel was 20 cm. This 20 cm portion was used as the artificial blood vessel of Comparative Example 4.

Comparative Example 5
As in Comparative Example 3, a PTFE trumpet-shaped tube was fabricated by the hot coining method, with the trumpet-shaped wall gradually thinning as shown in Figure 23. This trumpet-shaped tube was cut as shown in Figure 25 to fabricate a buffer cylinder with the smaller circumferential diameter of the stump on the upstream side of the buffer cylinder. In Comparative Example 5, the distance X was set to 0 (X÷Φ=R), i.e., X=0 mm. The upstream end of this buffer cylinder was adhesively fixed to a 6 mm inner diameter central portion of a commercially available conventional artificial blood vessel (Distaflo®, manufactured by C.R. Bard, Inc., with support). The conventional artificial blood vessel was then cut at a point within the buffer cylinder where the total length of the circumferential cylindrical portion and the conventional artificial blood vessel was 20 cm. This 20 cm portion was used as the artificial blood vessel of Comparative Example 5.

Comparative Example 6
A conventional, commercially available artificial blood vessel (Distaflo (registered trademark), manufactured by C.R. Bard, Inc., with support) was cut at a location where the length of the circumferential cylindrical portion, including the cuffed portion, was 20 cm, and this 20 cm portion was used as the artificial blood vessel of Comparative Example 6, which had an inner diameter of 6 mm (Distaflo (registered trademark) has a 1 mm taper in the inner diameter from 25 cm upstream of the cuff, so the inner diameter of the "7 mm inner diameter standard" artificial blood vessel for the 20 cm upstream of the cuff is 6 mm). In the case of Comparative Example 6, the distance X, X÷Φ=R, was set to 1.2.

Comparative Example 7
A portion of the cuff end of a conventional, commercially available artificial blood vessel (Distaflo (registered trademark), manufactured by C.R. Bard, Inc., with support) was removed, and the conventional artificial blood vessel was cut at a location where the length of the circumferential cylindrical portion, including the remaining cuff portion, was 20 cm. This 20 cm portion was used as the artificial blood vessel of Comparative Example 7, which had an inner diameter of 6 mm (Distaflo (registered trademark) has a 1 mm taper in the inner diameter from 25 cm upstream of the cuff, so the inner diameter of the "7 mm inner diameter standard" artificial blood vessel for the 20 cm upstream of the cuff is 6 mm). In the case of Comparative Example 7, the distance X was set to X÷Φ=R, which was 1.0.

Comparative Example 8
A portion of the cuff of a conventional commercially available artificial blood vessel (Distaflo (registered trademark), manufactured by C.R. Bard, Inc., with support) was resected and shortened as shown in Figure 25, and a buffer cylinder was formed with the opposite end of the trumpet-shaped stump on the upstream side. In the case of Comparative Example 8, the distance X was set to 0 (X÷Φ=R), i.e., X=0 mm. A portion of the circumferential cylindrical portion with a length of 20 cm and an inner diameter of 6 mm was used (Distaflo (registered trademark) has a 1 mm taper in the inner diameter from 25 cm upstream of the cuff, so the inner diameter of the "7 mm inner diameter standard" artificial blood vessel is 6 mm for the 20 cm upstream of the cuff).

Comparative Example 9
A 20 cm long cylindrical portion of a conventional, commercially available artificial blood vessel (Venaflo (registered trademark), manufactured by C.R. Bard, Inc., unsupported) including a cuffed portion was used as the artificial blood vessel of Comparative Example 9.

Comparative Example 10
For the comparative example, both ends of a commercially available artificial blood vessel (Soratec artificial blood vessel, code number 38435, model number 10002-6020-002, sold by Goodman Co., Ltd., Nagoya City) made of a reinforcing material added to a polyurethane tube with an inner diameter of 6 mm and a length of 20 cm was cut out to a length of 60 mm and connected to the downstream side of the same artificial blood vessel as Comparative Example 1, which was 140 mm long, to produce the artificial blood vessel of Comparative Example 10, having a total length of 200 mm.

Comparative Example 11
A commercially available conventional artificial blood vessel (Dacron (registered trademark) artificial blood vessel (J-Graft, Shield Neo S, manufactured by Japan Lifeline Co., Ltd.) with an inner diameter of 7 mm was cut to a length of 60 mm and used as a buffer cylinder for the "external overlapping juxtaposition type" of Comparative Example 11. That is, a portion with an inner diameter of 6 mm was cut from the center of the same conventional artificial blood vessel as in the other Examples to a length of 14 cm, and this artificial blood vessel was used to construct an arteriovenous shunt using a conventional artificial blood vessel between the external jugular vein and the common carotid artery. Next, a buffer system cylinder was placed on the outer periphery of the venous wall at a position 60 mm downstream from the downstream end of the conventional artificial blood vessel of this shunt, overlapping and juxtaposing it with the natural venous wall.

[Animal experiments]
Using the artificial blood vessels of the above Examples and Comparative Examples, animal experiments were carried out as follows.
Male or female beagle dogs weighing 12-16 kg and approximately one year old were used as experimental animals (hereinafter referred to as dogs). During the experiment, the dogs were housed individually and kept under standard conditions for at least one week before the experiment, with free access to standard dog chow and water.

<Experimental Method>
All the following surgical procedures were performed under aseptic conditions by a single surgical team. The dogs were given basal anesthesia with 35 mg/kg of pentobarbital intravenously, and a breathing tube was intubated into the trachea. They were then given general anesthesia with 40% oxygen and inhalation anesthesia with sevoflurane or isoflurane. Under general anesthesia, the dogs were fixed in an extended neck position and their abdominal hair was shaved. The skin was cleaned with 5% chlorhexidine in 80% ethanol and disinfected with 10% povidone-iodine.
A 15-cm vertical skin incision was made in the right or left side of the neck, the fascia and muscle were separated, and the external jugular vein and common carotid artery were exposed. An anastomotic shunt was created between the external jugular vein and the common carotid artery, as shown in Figure 26. After the shunt was created, the fascia and skin were sutured according to the natural anatomical structure, and the surgical incision was closed.
However, Examples 25 to 31 and Comparative Example 11 shown in Table 6 were installed using the installation method described in the respective production method paragraphs.
During surgery and periodically after surgery (basically every 4 weeks), observations were made with an ultrasound tomography system at the cardiac and cranial sides of the common carotid artery anastomosis, the arterial anastomosis end of the vascular graft, the midpoint of the vascular graft, the venous anastomosis end with the vascular graft, and downstream of the venous anastomosis with the vascular graft (i.e., the cardiac side) before and after shunt creation. Observations were recorded, including intravascular diameter, abnormal findings in the vascular wall (including abnormal wall thickening and wall irregularities), presence or absence of lumen stenosis/occlusion or thrombus formation, and vascular wall pulsation due to blood flow. Blood flow velocity and its waveform changes were also measured and recorded at the same sites using an ultrasound Doppler flowmeter. The time-dependent blood flow rate was calculated from the intravascular diameter and flow velocity waveform using built-in software.
After 12 weeks to 18 months of surgery, the dogs were euthanized with an intravenous injection of 100 mg/kg pentobarbital and autopsied. The shunt site was incised, and the vascular system in the area where the artificial blood vessel was implanted and the surrounding tissue were surgically removed en bloc to prepare a resected specimen for macroscopic and microscopic examination.
The resected specimens were evaluated macroscopically and under a stereomicroscope. The evaluation criteria were essentially the same as those evaluated using ultrasound imaging, but other pathological evaluation criteria were also added when necessary.
After this evaluation, the tissue was fixed in 10% neutral formalin solution, cut into 4 μm-thick microscopic sections using standard techniques, stained with hematoxylin and eosin (HE stain) and Elastica-van Gieson (EvG) stain, and observed under an optical microscope.

<Experimental Results>
The experimental results are shown below.
The results of the overall assessment were as follows: when all of the evaluation items (A) to (D) were satisfied, the case was judged as a successful overall assessment (◯ in the table), and when all other cases were satisfied, the case was judged as a failed overall assessment (× in the table). However, for Examples 25 to 31 and Comparative Example 11 listed in Table 6, when all of the evaluation items (A) to (D) as well as (E) were satisfied, the case was judged as a successful overall assessment (◯ in the table), and when all other cases were satisfied, the case was judged as a failed overall assessment (× in the table).

(Experimental result 1: Evaluation of shape and cushioning effect)
The buffering function of artificial blood vessels was evaluated using the shape of the buffer cylinder as an index.
The results are shown in Table 1 below.

The results in Table 1 above show that a cushioning effect was observed in the various shapes shown in Examples 1 to 11. The cushioning effect can be achieved by installing multiple identical shapes from Examples 1 to 11, or by appropriately combining other shapes from Examples 1 to 11. On the other hand, no cushioning effect was observed in the straight cylindrical shape made of ePTFE with a high elasticity index, such as conventional artificial blood vessels (Comparative Examples 1 and 2).

(Experimental Result 2: Evaluation of cushioning effect using 30% elasticity index)
The buffer function of a straight cylindrical buffer cylinder with an inner diameter of 6 mm and a length of 60 mm was examined using the 30% elasticity index as an index. Note that in Example 8, the height of the spiral projections is not included in the bore diameter.
The results are shown in Table 2 below.

A cushioning effect was observed over a wide range of 30% elasticity indices, from 0.08 to 10.1 N, as shown in Examples 1, 5, and 7-11. On the other hand, no cushioning effect was observed in conventional artificial blood vessels (Comparative Examples 1 and 2) where the 30% elasticity indices were 13.6 N or higher.

Examples 1, 5, and 7-11 all have a straight shape and are constructed with walls that are softer than conventional artificial blood vessels. The softness of the walls contributes to the cushioning effect, but it is also believed that the factors described below also contribute to the cushioning effect.

Example 7
Generally, in arteries, areas of high internal pressure move and are transmitted from upstream to downstream due to pulsatile blood delivery, and as a result, areas of the vascular wall that expand move and are transmitted downstream, resulting in wave-like lumen expansion. In the artificial blood vessel of Example 7, a section with a low elasticity value (the softest section with a 30% elasticity index of 0.08 N) is provided in the middle of the tube. When internal pressure is applied, this section expands more than other sections, providing the effect of a decompression chamber (buffer pool) that repeatedly expands in a pulsatile manner in response to the wave-like increase in internal pressure. The section downstream of this buffer pool, with a relatively high 30% elasticity index of 0.9 N, acts as a sluice gate at the buffer pool's outlet, enhancing its effectiveness. These effects enhance the buffering effect.

Example 1
As described above, pulsatile blood flow in the artery causes areas of high internal pressure to move from the upstream side to the downstream side, and as a result, areas of dilation in the vascular wall move downstream and are transmitted, resulting in wave-like lumen expansion. In the artificial blood vessel of Example 1, the wall thickness gradually decreases toward the downstream side, gradually changing to a softer state. In the artificial blood vessel of Example 1, the 30% elasticity index of the most upstream portion (closest to the artery) is 4.5 N, and the 30% elasticity index of the most downstream portion (closest to the vein) is 3.9 N. Therefore, the wave-like lumen expansion caused by this change in softness increases the further downstream. This effect of increasing wave-like lumen expansion downstream enhances the buffering effect.
Furthermore, if there is a large step in the change in softness, a large discontinuous change occurs in the wave-like lumen expansion at this step, which is likely to cause large turbulent blood flow at this area, and turbulent flow can cause thrombus formation.On the other hand, if the softness is changed gradually, the wave-like expansion moves and propagates smoothly, and large discontinuous changes do not occur, so blood turbulence is small, which has the advantage of reducing the risk of thrombus formation, etc.

Example 9
As described above, the artificial blood vessel of Example 9 was produced by applying a layer of silicone rubber around the iron core. The buffer cylinder had a right cylindrical shape and the elasticity of the wall was uniform.

Example 10
The artificial blood vessel of Example 10 has a wall that is thinner in two stages toward the downstream side. This produces the same effect as Example 1. In addition, the weave is very loose, and the openings of the windows in the loose mesh are sealed with soft glucomannan glue (containing an anticoagulant). The glucomannan windows that seal the loose mesh protrude outward under internal pressure (a structure similar to that shown in Figure 6; the lumen itself does not expand, but only the windows expand and protrude outward under pressure), enhancing the buffering effect.

Example 8
By creating a spiral groove in the lumen, the blood flows in a spiral pattern, enhancing the buffering effect, similar to that shown in Figure 5.

Examples 11 and 5
This example is similar to Example 8, but features a spiral compression/reinforcement material made of a non-stretchable fiber attached to the outside. As previously mentioned, pulsatile blood flow in arteries creates areas of high internal pressure, resulting in vascular wall lumen expansion. When a spiral compression/reinforcement material is attached to a vessel wall with a certain degree of flexibility from the outside, this lumen expansion due to internal pressure creates a spiral expansion-suppressing area. As a result, in addition to the pulsatile lumen expansion effect outward, blood flow becomes spiral, enhancing the cushioning effect as shown in Figure 5. The 30% elasticity index listed in Table 2 is largely due to the elasticity of the spiral reinforcement material, which is less stretchable than the wall material (in Example 5, the wall material is silicone rubber and the reinforcement material is polypropylene monofilament fiber; in Example 11, the wall material is polyurethane and the reinforcement material is silicone rubber), and the 30% elasticity index of the wall material is significantly lower than the elasticity index listed in Table 2.

Comparative Example 2 also has spiral reinforcement (support), but because the wall material is hard, the wall does not expand due to arterial pressure, and the cushioning effect seen in Examples 11 and 5 is not achieved. Incidentally, Example 2 is installed with the purpose of preventing the risk of blood clot formation or blood circulation interruption due to the blood vessel wall "collapsed" when the artificial blood vessel is twisted or compressed from the outside, causing the lumen to narrow or close.

Needless to say, the compression and reinforcement materials of Examples 11, 24, and 5 also have the effect of preventing thrombus formation and blood circulation disruption caused by twisting or compression of the artificial blood vessel. (This effect is extremely useful for buffer vessels with soft walls, where the risk of thrombus formation and blood circulation disruption caused by twisting or compression of the artificial blood vessel must be considered.)

(Experimental result 3: Buffering effect of the trumpet-shaped buffer cylinder using the relative length R of the buffer cylinder and the 30% elasticity index as indicators)
The buffering effect of the trumpet-shaped buffer cylinder was examined using the relative length R of the buffer cylinder and the 30% elasticity index as indicators.
The results are shown in Table 3 below.

(1) The relationship between the relative length of the buffer cylinder and its buffer effect was examined for a trumpet-shaped buffer cylinder with a configuration such as that shown in Figure 27. The ratio R (=X÷Φ) of the axial length X of the buffer cylinder to the inner diameter Φ of the blood inlet section, as shown in Figure 28, was used as an indicator of the buffer cylinder's relative length. Even for trumpet-shaped buffer cylinders made of the same PTFE material and with the same 30% elastic index of 11.8 N, a buffer effect was observed when the buffer cylinder's relative length R = X÷Φ ≥ 1.5 (Examples 12 and 13), but not when R = X÷Φ ≤ 1.2 (Comparative Examples 3 to 5). Furthermore, when R = X÷Φ ≤ 1.2, no buffer effect was observed in Comparative Examples 6 to 9, which were made of ePTFE and had a higher 30% elastic index of 12.0 N or higher. This indicates that when the trumpet-shaped configuration and 30% elastic index of 11.8 N or higher are used, a buffer effect can be achieved if the buffer cylinder's relative length R ≥ 1.5 is met.
(2) The relationship between the 30% elasticity index and the cushioning effect of the trumpet-shaped buffer cylinder was examined. A cushioning effect was observed even when R<1.5, such as in Example 14 (R=1) where the 30% elasticity was low at 7 N, and in Example 15 (R=0) where it was 3.9 N. On the other hand, even when the relative length R of the buffer cylinder was the same (R<1.5) and the 30% elasticity index of the buffer cylinder was high at 11.8 N or higher (Comparative Examples 3 to 9), no cushioning effect was observed. In other words, a lower 30% elasticity index is required for a buffer cylinder with a relative length R<1.5 to exhibit a cushioning effect. This indicates that a cushioning effect is observed when the 30% elasticity index is 7 N or lower when R=1, and when R=0, a 30% elasticity index of 3.9 or lower.

(Experimental result 4: Changes in wall thickness of the trumpet-shaped buffer cylinder and buffering effect)
The change in wall thickness and the buffering effect of the trumpet-shaped buffer cylinder were investigated.
The results are shown in Table 4 below.

The relationship between changes in the thickness of the trumpet-shaped buffer cylinder wall and its buffering effect was examined when the relative length R of the buffer cylinder was ≦1.2. When considering trumpet-shaped buffer cylinders made of the same PTFE material and when the relative length R of the buffer cylinder was ≦1.2, a buffering effect was observed when the wall thickness was made thinner on the lateral side within the same cross section perpendicular to the axial direction (Examples 16 to 18), regardless of the value of the relative length. However, when the side wall thickness did not change as described above within the same cross section, no buffering effect was observed when the relative length R of the buffer cylinder was ≦1.2, regardless of the value of the relative length (Comparative Examples 3 to 5).

(Experimental Result 5: Evaluation of cushioning effect by elasticity index of 60%, 100% and 150%)
Examples and comparative examples for 60%, 100% and 150% elasticity index are shown in the table below. The evaluation method is the same as that for 30% elasticity index.

Example 24 in Table 5 has a straight shape, an inner diameter of 6 mm, and a length of 60 mm, but includes a buffer cylinder whose wall elasticity changes in a spiral pattern. This spiral change is thought to enhance the buffering effect, and considering this, in order to have a buffering effect, it is necessary for the buffer cylinder wall to satisfy at least one of the following conditions: a 60% elastic index of 4.6 N or less, a 100% elastic index of 7.5 N or less, or a 150% elastic index of 9.8 N or less (Example 23).
Examples 20, 21, 22, and 23 in Table 5 are the experimental results for cases where the cylinder is straight and there is no change in shape or elasticity, i.e., where the cushioning effect is achieved solely through uniform wall elasticity. Referring to these results, the indicators for a cushioning cylinder with an inner diameter of 6 mm and a length of 60 mm that demonstrate a cushioning effect solely through uniform wall elasticity are, as a minimum, a 60% elasticity index of 3.2 N or less, a 100% elasticity index of 6.5 N or less, and a 150% elasticity index of 9.8 N or less; more preferably, a 60% elasticity index of 1.6 N or less, a 100% elasticity index of 2.5 N or less, and a 150% elasticity index of 8.4 N or less; and even more preferably, a 60% elasticity index of 0.8 N or less, a 100% elasticity index of 1.5 N or less, and a 150% elasticity index of 4.6 N or less.
In Comparative Examples 10, 1 and 2, which used conventional artificial blood vessels, the elasticity indexes did not satisfy the above conditions, and no cushioning effect was observed.

(Experimental result 6: Evaluation of the buffering effect of layered, parallel-arranged buffer cylinders)
The buffering effect of layered, parallel-placed buffer cylinders is shown in the table below.

The examples in Table 6 are all buffer system artificial blood vessels with overlapping juxtaposed buffer cylinders that are placed side by side on top of the vein wall, and are hybrid buffer system artificial blood vessels that not only have the "physical buffering effect" of the installed buffer cylinders but also a significant "biological buffering effect" of remodeling the natural vein.
Of these, Examples 25 to 29 are what might be called "external overlapping apposition type" or "external stent type," which are placed on the outer periphery of the venous wall in overlapping relation to the venous wall. After placement, the buffer cylinder has a cross-section of the desired cylindrical shape, such as a circle or ellipse. However, before placement, the shape has a discontinuous line in the wall of the cylindrical portion, i.e., a slit that starts at one end of the cylinder and continues to the other end. The advantage of this slit is that it allows for re-placement and adjustment of the placement state.
Without the "gap," reinstallation would require disrupting the continuity between the conventional vascular graft and the vein, reinstalling a new buffer cylinder around the vein, and then re-anastomosing the vascular graft to the vein after installation. However, with the "gap," the cylinder can be opened, for example, into a single coiled tape, and the tape can be simply "covered" or "wrapped" around the vein wall. This eliminates the need to disrupt the continuity between the vascular graft and the vein, and eliminates the need for re-anastomosing. Furthermore, as mentioned above, the placement can be adjusted by utilizing the "gap" while evaluating the blood flow status using an ultrasound blood flow system, allowing for optimal placement to achieve the desired blood flow status.
Furthermore, if the installed "seamless" buffer cylinder is not expected to achieve the desired blood flow condition due to an improper installation condition, such as being "too loose," it is possible to correct the "too loose" installation condition and adjust it to an appropriate installation condition that achieves the desired blood flow condition by layering part or all of a "slit" buffer cylinder on top of the previously installed "seamless" buffer cylinder.
The remaining Examples 30 and 31 listed in Table 6 are what should be called "internal overlapping apposition type" or "internal stent type," which are overlapped and apposed to the venous wall on the lumen side of the venous wall. This type can also be deformed into an elongated shape by stretching it in the longitudinal direction without necessarily creating a "slit," and can be deformed into an elongated shape even without a slit by puncturing the blood vessel wall to create a small hole, allowing it to be re-installed in the venous lumen or the installation state to be readjusted, but Examples 30 and 31 have a "slit."
The results of the animal experiment evaluation showed that all of Examples 25 to 31 satisfied not only the individual evaluation results (A) to (D) but also (E), confirming the buffering effect of the buffer-type artificial blood vessels, confirming their effectiveness, and confirming their biological buffering action.
In particular, in Example 26, at the time of evaluation after 12 months, the PGA nonwoven fabric and alginic acid had been almost completely decomposed and absorbed, indicating that the natural veins that had been remodeled into buffering blood vessels were independently exerting a buffering function.
From the above experimental results, the minimum conditions for a buffer cylinder that is placed juxtaposed to the venous wall to exhibit a buffering effect are that the buffer cylinder wall has a 30% elasticity index of 3.1 N or less, a 60% elasticity index of 4.2 N or less, a 100% elasticity index of 6.2 N or less, or a 150% elasticity index of 8.9 N or less; more preferably, the buffer cylinder wall has a 30% elasticity index of 1.5 N or less, a 60% elasticity index of 1.6 N or less, a 100% elasticity index of 3.3 N or less, or a 150% elasticity index of 8.2 N or less; and even more preferably, the buffer cylinder wall has a 30% elasticity index of 0.53 N or less, a 60% elasticity index of 1.4 N or less, a 100% elasticity index of 2.7 N or less, or a 150% elasticity index of 3.9 N or less.
In Comparative Example 11, which used a conventional commercially available artificial blood vessel, the elasticity indexes did not satisfy the above conditions, and no cushioning effect was observed.

<Evaluation of animal experiments>
According to the following criteria, it was evaluated whether the artificial blood vessel interposed at the site of shunt construction acted as a low-pressure buffer vessel and prevented pathological changes in the blood vessel at the shunt site.
Beagle dogs (weight 12-16 kg) were used. A shunt using an artificial blood vessel with the anastomosis configuration shown in Figure 26 was constructed between the carotid artery and jugular vein, and the dogs were observed over time. During the observation period, the following assessments were made using a color Doppler blood flowmeter and a color Doppler ultrasound tomography diagnostic device. At the end of the observation period, the dogs were euthanized and evaluated.
The vascular system of the shunt site of euthanized dogs was excised. The vascular system, including the carotid artery, the entire length of the artificial blood vessel, and the vein extending 70 mm from just below the anastomosis in the direction of blood flow, was examined and evaluated macroscopically and under a stereomicroscope at up to 10x magnification, both in the excised state and with the lumen open. The vascular walls of the excised vascular system were then prepared into standard 4-μm-thick thin sections for microscopic examination, stained with hematoxylin and eosin and Elastica van Gieson (EvG) staining, and examined under a light microscope.

<Evaluation criteria>
If all of the following evaluation items (a) to (d) were met, the artificial blood vessel interposed at the shunt creation site acted as a low-pressure buffer vessel and was judged to be a successful case (○ in Table 1) in which pathological changes in the blood vessels at the shunt site were prevented; otherwise, it was judged to be a failure (× in Table 1).
(A) In the measurement using the ultrasonic color Doppler blood flowmeter shown in Figure 26, (1) the blood flow in the carotid artery is an antegrade flow from the heart side to the head side at both the central side of the anastomosis between the carotid artery and the artificial blood vessel, i.e., the heart side of the carotid artery (blood flow measurement site 1 in Figure 26), and the peripheral side, i.e., the head side of the carotid artery (measurement site 2 in Figure 26), and (2) as a finding that the arterial pulsatile blood flow is buffered, both the average velocity of the blood flow and the average change in blood flow pulsation are less than half of the values in the jugular vein (blood flow measurement site 3 in Figure 26) anastomosed to the artificial blood vessel, which is on the downstream side, compared to the blood flow in the carotid artery, which is on the upstream side (blood flow measurement site 1 in Figure 26).
(a) In the ultrasound tomographic imaging diagnosis, the vascular lumen is patent, the vascular wall is smooth, and there are no pathological findings affecting blood flow from the artificial blood vessel to the jugular vein, such as intimal hyperplasia, thrombus formation, luminal stenosis, or varicose vein formation.
(c) Upon macroscopic examination, the vascular lumen is patent, the vascular wall is smooth and free of varicose veins or unnatural irregularities, and there are no pathological findings that affect blood flow, such as intimal hyperplasia, thrombus formation, or luminal narrowing.
(d) Observations under a stereomicroscope and a normal optical microscope show that the vascular lumen is patent, the vascular wall is smooth and free of varicose veins or unnatural irregularities, and there is no pathological finding affecting blood flow such as intimal hyperplasia, thrombus formation, or stenosis.
However, in cases where a "biological buffering effect" is deemed to have been observed in an experimental case that has been judged to be successful, the microscopic findings described below as (e) must also be observed.
(E) The vein at the site of the shunt creation is excised and stained with hematoxylin and eosin and Elastica-van Gieson (EvG) staining, followed by microscopic observation. The observation sites are three: a section from the upstream end of the buffer cylinder of the buffer system vessel overlying the vein at the site of the shunt creation to 10 mm downstream in the direction of blood flow, a section from the other end of the buffer cylinder to 10 mm upstream in the direction of blood flow, and a section within the 10 mm point exactly midway between these two. The cross section of the vessel is observed with an optical microscope, and the following two findings (A) and (B) are confirmed at each of the three observation sites: (A) A two-layer structure is confirmed, with a smooth muscle layer containing abundant elastic fibers on the luminal side and an elastic fiber layer containing collagen fibers on the outer side. (B) Furthermore, at each observation site, the outer elastic fiber layer containing collagen fibers is thicker than the inner smooth muscle layer.

<Details of Experimental Results for Representative Examples and Comparative Examples>
For reference, detailed experimental results of representative examples and comparative examples are shown below.
Example 1
(1) Evaluation results by item (a) Evaluation by ultrasonic Doppler blood flow meter
(i) Ultrasound tomography imaging diagnosis: No abnormal findings.
(c) Macroscopic findings at autopsy: No abnormal findings.
(e) Microscopic findings: No abnormal findings.
(2) Overall assessment: The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

Example 2
(1) Evaluation results by item (a) Evaluation by ultrasonic Doppler blood flow meter
(i) Ultrasound tomography imaging diagnosis: No abnormal findings.
(c) Macroscopic findings at autopsy: No abnormal findings.
(e) Microscopic findings: No abnormal findings.
(2) Overall assessment: The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

Example 5
(1) Evaluation results by item (a) Evaluation by ultrasonic Doppler blood flow meter
(i) Ultrasound tomography imaging diagnosis: No abnormal findings.
(c) Macroscopic findings at autopsy: No abnormal findings.
(e) Microscopic findings: No abnormal findings.
(2) Overall assessment: The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

Example 9
(1) Evaluation results by item (a) Evaluation by ultrasonic Doppler blood flow meter
(i) Ultrasound tomography imaging diagnosis: No abnormal findings.
(c) Macroscopic findings at autopsy: No abnormal findings.
(e) Microscopic findings: No abnormal findings.
(2) Overall assessment: The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

Example 12
(1) Evaluation results by item (a) Evaluation by ultrasonic Doppler blood flow meter
(i) Ultrasound tomography imaging diagnosis: No abnormal findings.
(c) Macroscopic findings at autopsy: No abnormal findings.
(e) Microscopic findings: No abnormal findings.
(2) Overall assessment: The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

Example 16
(1) Evaluation results by item (a) Evaluation by ultrasonic Doppler blood flow meter
(i) Ultrasound tomography imaging diagnosis: No abnormal findings.
(c) Macroscopic findings at autopsy: No abnormal findings.
(e) Microscopic findings: No abnormal findings.
(2) Overall assessment: The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

(Example 27)
(1) Evaluation results by item (a) Evaluation by ultrasonic Doppler blood flow meter
(i) Ultrasound tomography imaging diagnosis: No abnormal findings.
(c) Macroscopic findings at autopsy: No abnormal findings.
(e) Microscopic findings: No abnormal findings.
(E) Microscopic findings: Findings (A) and (B) were observed at all three designated observation sites, and it was determined that the vascular system was remodeling to a low-pressure buffering system.
(A) A photograph of the EvG stained central part of the buffer cylinder (Fig. 29) shows a two-layer structure with a smooth muscle layer containing abundant elastic fibers on the luminal side and an elastic fiber layer containing collagen fibers on the outer side.
(B) A table (Table 14) of the thickness of the smooth muscle and elastic fiber layer containing collagen at the three observation sites is presented.
At all three observation sites, the thickness of the elastic fiber layer was greater than the thickness of the smooth muscle layer.
(2) Overall assessment: The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.
It was confirmed that biological buffering action was at work.

(Comparative Example 1)
(1) Evaluation results by item (a) Evaluation by ultrasonic Doppler blood flow meter
(i) Ultrasound imaging diagnosis: Thickening of the venous wall and prominent varicose veins were observed, with a blood clot inside the veins.
(c) Macroscopic findings at autopsy: Significant varicose veins were observed on the venous side, with thrombus inside.
(e) Microscopic findings: Thickening of the venous wall and varicose veins are observed.
(2) Overall assessment: No buffering effect of the shunt vessel was observed, and the procedure was ineffective.

(Comparative Example 2)
(1) Evaluation results by item (a) Evaluation by ultrasonic Doppler blood flow meter
(i) Ultrasound imaging diagnosis: The lumen of the artificial blood vessel and the lumen of the vein were completely blocked.
(c) Macroscopic findings at autopsy: The lumen from the artificial blood vessel to the vein was completely blocked.
(e) Microscopic findings: Pathological intimal hyperplasia and old thrombus were found in the vein, which led to the determination that the lumen had been completely blocked.
(2) Overall assessment: The lack of a buffering effect caused intimal hyperplasia, resulting in complete occlusion of the shunt vessel.

(Comparative Example 3)
(1) Evaluation results by item (a) Evaluation by ultrasonic Doppler blood flow meter
(i) Ultrasound imaging diagnosis: Thickening of the venous wall and prominent varicose veins were observed.
(c) Macroscopic findings at autopsy: Thickened and irregular venous walls and prominent varicose veins were observed.
(e) Microscopic findings: Pathological intimal thickening of the veins and varicose veins are observed.
(2) Overall assessment: No buffering effect of the shunt vessel was observed, and the procedure was ineffective.

1 to 7 Buffer system artificial blood vessel 10 Buffer cylinder 20 Normal path section

Claims (23)

A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein,
the function of buffering hemodynamics is a function of reducing the pressure and pulsatile changes in pressure, and/or the flow rate and magnitude of the change in flow rate of blood flowing in from the arterial side, and allowing the blood to flow out to the venous side;
The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof,
The buffer cylinder has a portion having a 30% elasticity index of 10.1 N or less.
Buffer system artificial blood vessel. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein,
The function of buffering hemodynamics is to reduce the pressure and pulsatile changes in pressure, and the flow rate and magnitude of the change in flow rate of blood flowing in from the arterial side, and to allow the blood to flow out to the venous side.
Buffer system artificial blood vessel. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein,
The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof,
The buffer cylinder has a portion having a 30% elasticity index of 10.1 N or less.
The buffer system artificial blood vessel according to claim 2 . A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein,
The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof,
The buffer cylinder has a portion having a 100% elasticity index of 7.5 N or less.
4. The buffer system artificial blood vessel according to claim 1. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein,
The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof,
The buffer cylinder has a portion having a 60% elasticity index of 4.6 N or less.
5. The buffer system artificial blood vessel according to claim 1. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein,
The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof,
The buffer cylinder has a portion having a 150% elasticity index of 9.8 N or less.
6. The buffer system artificial blood vessel according to claim 1. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein,
The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof,
The buffer cylinder has an artificial blood vessel wall in which the elastic index of the artificial blood vessel wall on the venous side is smaller than the elastic index of the artificial blood vessel wall on the arterial side.
7. The buffer system artificial blood vessel according to claim 1. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein,
The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof,
8. A buffer system artificial blood vessel according to claim 1, wherein the buffer cylinder has an artificial blood vessel wall in which the elastic index of the artificial blood vessel wall on the venous side is greater than the elastic index of the artificial blood vessel wall on the arterial side. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein,
The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof,
9. The buffer system artificial blood vessel according to claim 1, wherein the buffer cylinder has a portion whose inner diameter increases from the arterial side to the venous side and/or a narrow portion whose inner diameter decreases from the arterial side to the venous side. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein,
The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof,
The buffer cylinder has a spiral-shaped inner cavity.
10. The buffered vascular prosthesis according to any one of claims 1 to 9. 11. The buffer system artificial blood vessel according to claim 1 , wherein the buffer cylinder has portions with different elasticity combined in a patch-like manner. 12. The buffer system artificial blood vessel according to claim 1, 3 or 3 to 11, wherein the buffer cylinder has an elliptical cross section, and the elliptical cross section has a wall thickness different between the major axis side and the minor axis side. 13. The buffer system artificial blood vessel according to claim 1 , wherein the buffer cylinder has a wall thickness that varies in the axial direction. 14. The buffer system artificial blood vessel according to claim 1, wherein the buffer cylinder has an axial length of X mm and an inner diameter of the blood inlet of Φ mm, and the ratio R (=X/Φ) thereof is 1 or greater. A buffer-type artificial blood vessel according to any one of claims 1 to 14, wherein the artificial blood vessel material contains two or more types of fibers with different elastic properties. A buffer-type artificial blood vessel according to any one of claims 1 to 15, comprising an elastomer as a material for the artificial blood vessel. A buffer-type artificial blood vessel according to any one of claims 1 to 16, comprising a biodegradable material as a material for the artificial blood vessel. A buffer-type artificial blood vessel according to any one of claims 1 to 17, wherein the artificial blood vessel wall has a continuous or discontinuous spiral or segmental reinforcing structure or a valve-like structure. A buffer-type artificial blood vessel according to any one of claims 1 to 18, wherein part or all of the artificial blood vessel wall has a layered structure consisting of two or more layers, and the layered structure has a structure in which the overlapping layers are offset from each other. A buffer system artificial blood vessel according to any one of claims 1 to 19, in which a buffer cylinder, which functions to buffer the dynamics of blood flowing from an artery to a vein, has slits formed therein that allow the artificial blood vessel wall to be separated. The buffer system artificial blood vessel described in claim 20, wherein the buffer cylinder having the cuts formed therein satisfies at least one of the following conditions at least in part: a 30% elastic index of 3.1 N or less, a 60% elastic index of 4.2 N or less, a 100% elastic index of 6.2 N or less, and a 150% elastic index of 8.9 N or less. The buffer-system artificial blood vessel according to claim 20 or 21, wherein at least a portion of the buffer cylinder on which the slits are formed is made of a bioabsorbable material or metal. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein,
The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof,
23. A buffer system artificial blood vessel according to any one of claims 1 to 22, wherein the buffer cylinder has elasticity such that, when its inner diameter expands to 130% in 100 seconds due to an external force of a certain strength, it returns to an inner diameter smaller than 125% of its inner diameter within 200 seconds after the external force is removed, and/or, when its inner diameter contracts to 80% in 100 seconds due to an external force of a certain strength, it returns to an inner diameter larger than 85% of its inner diameter within 200 seconds after the external force is removed.