JPH0554339B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a non-invasive continuous blood pressure monitor that continuously measures blood pressure in a non-invasive manner via a finger or the like.

[Prior art and its problems]

Conventional non-invasive continuous blood pressure monitor (Special Publication No. 59-5296)
In this method, external pressure is continuously applied using a cuff, etc., and servo control is performed so that the external pressure at the measurement site is the same as the arterial blood pressure, and continuous measurements are performed using the external pressure at that time as the blood pressure value. In this case, the measurement site was squeezed with the same pressure as the arterial blood pressure, causing congestion and physical pain. Furthermore, when measuring with a finger, arterial blood pressure changes due to blood congestion, resulting in measurement errors. Therefore, at present, it is necessary to interrupt the measurement every 10 minutes, for example, to relieve the congestion, making continuous measurement for a long time of 10 minutes or more difficult.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned shortcomings of the prior art, and its purpose is to continuously measure blood pressure by keeping the external pressure at the measurement site lower than the arterial blood pressure. It is an object of the present invention to provide a non-invasive continuous blood pressure monitor that eliminates measurement errors due to oxidation, minimizes measurement site restriction, and enables stable measurement over a long period of time.

[Summary of the invention]

In order to achieve the above object, the present invention provides a cuff attached to a part to be measured, a pressure sensor that detects the internal pressure of the cuff, a pressure control means that increases or decreases the internal pressure of the cuff, and a cuff that is attached to the part to be measured. a volume sensor inserted into a site to detect intravascular volume changes that vary with pulsation of a blood vessel in the measurement site; and a control means for servo-controlling the pressure control means based on the output of the volume sensor; The control means includes a first cuff pressure detection means for detecting a first cuff pressure P _c1 at which the volume pulse wave amplitude of the volume sensor output is maximum, and a second cuff pressure P _c2 lower than the first cuff pressure P _c1 .
is applied to the cuff, the average value of the volume sensor output is set as a servo target value, and the pressure control means is servo-controlled so that the volume pulse wave amplitude is minimized based on the volume sensor output signal, a second cuff pressure detection means for continuously detecting the cuff pressure at which the volume pulse wave amplitude becomes equal to or less than a predetermined value; the cuff pressure detected by the second cuff pressure; and the first cuff pressure.
The blood pressure calculation means is characterized in that the blood pressure calculation means calculates the measured blood pressure value as the sum of the value obtained by subtracting the second cuff pressure P _c2 from P _c1 .

In this case, the second cuff pressure P _c2 can be set to a value obtained by subtracting a constant pressure from the first cuff pressure P _c1 . Further, the second cuff pressure P _c2 can be set to a cuff pressure at which the volume pulse wave amplitude becomes approximately 1/2 of the maximum value.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

According to the so-called volume compensation method, external pressure is applied from outside the body to keep the pulsating intravascular volume constant.
Continuous measurement of blood pressure is possible by measuring external pressure in a state where external pressure and intravascular pressure (blood pressure) are balanced. The operating principle of the present invention is based on this volume compensation method, and it is possible to continuously measure blood pressure while keeping the extracorporeal pressure (cuff pressure) lower than before.The principle is as follows.

If we ignore the incompressibility of the blood vessel wall from elasticity theory, then V−V=2π/E・R ₁ ²・R ₂ ² R ₁ ² −R ₂ ²・(Pb−
Pc)...The relational expression (1) holds true. Here, R1: Blood vessel inner diameter R2: Blood vessel outer diameter V: Intravascular volume V0: No-load intravascular volume Pb: Intravascular pressure Pc: External pressure (cuff pressure) E: Complex modulus of elasticity of blood vessel. Therefore, from equation (1), when V=V0, Pb=Pc, and the conventional volume compensation method detects the extra-body pressure Pc at this time to determine the intravascular pressure. That is,
A cuff pressure Pc of the same magnitude was applied to cancel the intravascular pressure Pb.

Now, if we set V=V0+ΔVc, then from equation (1), ΔVc=2π/E・R ₁ ²・R ₂ ² /R ₁ ²・(Pb−Pc) =1/k(Pb−Pc) …(2 ) However, 1/K=2π/E・R ²・R ₂ ² /R ₁ ² −R ₂ ² ∴Pc=KΔVc+Pc (3) where KΔVc is the load applied to the blood vessel wall. Therefore, Pb can be measured continuously from KΔVc and Pc. In this case, when the intravascular volume change ΔV is measured while applying the average external pressure, ΔV shows the maximum value ΔKmax when the average external pressure = average intravascular pressure, and the average intravascular volume at this time is the intravascular volume under no load V0 matches. If the mean external pressure is further reduced from this point, the mean intravascular volume will increase to V0+. That is, when the relationship =+...(4) holds, the relationship =0+...(5) holds true. Therefore, by comparing equations (3) and (4), we can say that KΔVc=. Therefore, in this state, if the external pressure Pc is servo-controlled to cancel out the change ΔV in the intravascular volume V, the intravascular volume V becomes
The pressure at this time is held at V0+ (cuff pressure)
If Pc is continuously measured, blood pressure Pb can be continuously measured since Pb=Pc+.

1 to 3 relate to an embodiment of the present invention, and FIG. 1 is a block diagram showing a continuous blood pressure monitor of the embodiment. In the figure, 1 is a cuff adapted to the shape of the finger at the site to be measured, 2 is a pressure sensor that examines the pressure inside the cuff 1, and 3 is a device that irradiates light into the arterial blood flow of the finger.
LED, 4 is a phototransistor that detects reflected light or transmitted light from arterial blood flow, 5 is a volume sensor that detects intravascular volume changes from the output of phototransistor 4, 6 is a diaphragm pump that servo controls the cuff internal pressure, 7 is a diaphragm A moving coil that servo drives the pump 6, a coil driver 8 that drives the moving coil 7, a roller pump 9 that accelerates and depresses the cuff internal pressure at a constant speed, and a tank 10 that stores liquid (water) to be filled into the cuff. , 11 is a motor driver that drives the roller pump 9 at a constant speed, 1
2 is an A/D converter that digitally converts the pressure sensor signal PC and the volumetric sensor signal PG; 13 is a central processing unit (CPU) that realizes an example of the control of the present invention by executing the program of the embodiment in FIG. 3; and 14 15 is a D/A converter that converts the control information output from the CPU 13 into an analog signal, 15 is a servo amplifier that performs servo control so that the intravascular volume (signal PG) becomes a constant target value (V0+), and 16 is for servo control. 17 is an automatic servo gain control circuit (AGC) that activates/deactivates the servo loop and requests servo gain; 18 continuously digitalizes, for example, the systolic blood pressure SYS and diastolic blood pressure DIA for each beat; 19 is an addition circuit that adds an offset pressure correction value ΔPc to the detected cuff pressure signal PC to form an actual pressure signal (PC+); 20 is a blood pressure signal terminal that outputs a signal to an external storage device, etc. .

FIG. 2 is a timing chart showing operation signals of the embodiment. When you insert your finger inside cuff 1,
A certain amount of liquid is filled inside the cuff 1, and a roller pump 11 is further controlled by the CPU 13.
Pressurization is started by driving (t0). In this state, the volume sensor 5 detects the intravascular volume of the finger artery based on the output of the phototransistor 4 configured between the inner periphery of the cuff 1 and the inserted finger. The volume signal PG output from the volume sensor 5 is sent to the CPU 1 via the A/D converter 12.
3 and is monitored. Here, the volume signal
The point in time when the PG pulse wave component PGac reaches its maximum (e.g.
The average cuff _c1 (first cuff pressure) at t4) is the average external pressure (=average intravascular pressure) used in the conventional volume compensation method. Based on this state, the CPU 13 further reduces the cuff pressure to a predetermined average cuff pressure _c2 (second
The roller pump control is stopped when the cuff pressure is reached (cuff pressure), and thereafter the servo control is activated to maintain the pulsating intravascular volume at a constant target value (t5).

The predetermined average cuff pressure _c2 may be determined by subtracting a constant pressure from the cuff pressure _c1 , for example.
In this way, a cuff pressure suitable for long-term continuous measurement can be easily selected. Alternatively, the cuff pressure at which the volume pulse wave amplitude becomes approximately 1/2 of the maximum value may be used. In this way, an effective volume pulse wave signal can still be used for servo control, allowing highly accurate and reliable blood pressure measurement.

In any case, from this point on, servo amplifier 1
The intravascular volume signal PG is led to the negative input terminal of 5,
Its positive input terminal is connected to the servo target value (V0
+) is input. As a result, the output of the servo pump 15 works to eliminate the pulse wave component of the intravascular volume signal PG, and together with the actions of the phase compensation circuit 16 and automatic servo gain control circuit (AGC) 17, the output of the servo pump 15 works to eliminate the pulse wave component of the intravascular volume signal PG. is maintained almost at a constant target value (V0+). (t6). That is, from this point on, the equilibrium state of intravascular and extravascular pressures is maintained.

On the other hand, the cuff pressure signal PC of the pressure sensor 2 output is also A/
The data is read into the CPU 13 via the D converter 12 and monitored. The CPU 13 obtains the difference ΔPc (= _c1 - _c2 ) between the average cuff pressure _c1 obtained at timing t4 and the average cuff pressure _c2 obtained at timing t5 (t5),
After t6 when the servo is achieved, the patient's systolic blood pressure SYS is calculated by adding the difference ΔPc to the cuff pressure signal PG for each beat.
and continuous digital display of diastolic blood pressure DIA.
Further, by outputting the difference to the adding circuit 9, a continuous blood pressure signal is formed at the blood pressure signal terminal 20.

FIG. 3 is a flowchart showing the continuous blood pressure measurement control procedure of the embodiment. After inserting a finger into cuff 1, measurement starts and the main process begins. In step s1, the roller pump 9 starts rapidly pressurizing the cuff 1 (t0).
As a result, the intravascular volume signal PG also rises, and at the same time, the volume pulse wave component PGac due to digital artery pressure is superimposed (t1). In step s2, changes in the amplitude of this volume pulse wave component PGac are monitored. When cuff pressure is continued, the maximum amplitude point (t2) of the volume pulse wave component PGac
appears, and as pressure is applied further, the amplitude gradually decreases. In step s3, it is detected that the amplitude of the volume pulse wave component becomes approximately 1/2 of the maximum value, and when this judgment is satisfied, the rapid pressurization is stopped, and in step s4, low-speed decompression (for example, -3 mmHg/sec) is started ( t3). In step s5, the amplitude change of the volume pulse wave component PGac is further monitored. Then, due to a decrease in external pressure, the maximum point of the volume pulse wave amplitude appears again. (t4). As described above, the average cuff pressure _c1 at this point can be considered to be equal to the average intravascular pressure. Further, as described above, the average intravascular volume 1 at this time can also be regarded as the intravascular volume V0 under no load. At step s6, the maximum point of the volume pulse wave amplitude is detected.The process proceeds to step s7, and the average cuff pressure _c1 and average intravascular volume at that point are determined.
V1 is determined (first cuff pressure detection means) and stored in the memory (not shown) of the CPU 13 for later use.
In step s8, the volume pulse wave component is further measured under cuff decompression.
Changes in the amplitude of PGac are monitored, and in step s9 it is waited until the amplitude becomes approximately 1/2 of its maximum value. Eventually, when the determination in step s9 is satisfied, step s
Proceed to step 10, stop the roller pump 9,
Thereafter, the average cuff pressure is maintained at the cuff pressure _c2 at that point.

Note that at this point, a method of detecting a point where the pressure has been further reduced by a constant pressure ΔPc (for example, −30 mmHg/sec) from the average cuff pressure _c1 may be used.

In step s11, the minute portion of the average cuff pressure,
and the corresponding increase in intravascular volume are calculated and stored in memory. In step s12, the servo target value V2=V0+ of the intravascular volume signal PG is output to the positive input terminal of the servo amplifier 15, and in step s13, the AGC 17 is energized to form a servo loop. Further, in step s14, the blood pressure correction value is outputted to the adding circuit 19 so that a blood pressure signal can be formed. In step s15, changes in the amplitude of the volume pulse wave component PGac are monitored again. In this state, the servo loop operates to cancel the volume pulse wave signal based on the volume pulse wave signal. That is, the pulse wave amplitude gradually decreases and the servo drive is performed via the diaphragm pump 6 so that the intravascular volume becomes a constant value (V0+). In step s16, the process waits until the volume pulse wave signal amplitude becomes within a certain level (approximately 0). Eventually, when the determination at step s16 is satisfied (t6), step s
17. Proceed to step s18, and display systolic blood pressure SYS (=Pcmax+) and diastolic blood pressure DIA (=
Pcmi+) (second cuff pressure detection means and blood pressure calculation means). In step s19, it is determined whether there is an instruction to end the measurement (not shown) from the outside. If there is no instruction, the process returns to step s15, and the blood pressure display for each beat is repeated in the same manner as described above. If there is a termination instruction, the process proceeds to step s20.
The AGC 17 is deenergized, and the process proceeds to step s21, where the cuff 1 is rapidly decompressed by the roller pump 9.

Although the device of the above embodiment uses a finger, it can also be applied to the measurement of central blood pressure such as the upper arm or wrist, or to other measurement sites.

〔Effect of the invention〕

As explained above, according to the present invention, continuous blood pressure measurement is performed by tightening the measurement site with a pressure lower than the arterial blood pressure.
There is no blood pressure and measurement errors caused by it, the restraint of the measurement site is minimized, and there is an effect that non-invasive continuous blood pressure measurement can be performed stably over a long period of time.

[Brief explanation of the drawing]

Fig. 1 is a block configuration diagram showing a continuous blood pressure monitor according to an embodiment, Fig. 2 is a timing chart showing operation signals of the embodiment, and Fig. 3 is a flowchart showing a continuous blood pressure measurement control procedure according to an embodiment. It's a chat. 1...Cuff, 2...Pressure sensor, 3...LED, 4...
Photo transistor, 5... Volume sensor, 6... Diaphragm pump, 7... Moving coil, 8... Coil driver, 9... Roller pump, 10... Tank, 11... Motor driver, 12... A/D converter,
13... Central processing unit (CPU), 14... D/A converter, 15... Servo amplifier, 16... Phase compensation circuit, 17... Automatic servo gain control circuit (AGC), 18... Liquid crystal display, 19...
Addition circuit 20...Blood pressure signal terminal.

Claims (1)

[Scope of Claims] 1. A cuff attached to a site to be measured, a pressure sensor for detecting the internal pressure of the cuff, a pressure control means for increasing or decreasing the internal pressure of the cuff, and a cuff inserted between the cuff and the site to be measured. A volumetric sensor that detects intravascular volume changes that vary with the pulsation of the blood vessel in the measurement site, and a control unit that servo-controls the pressure control unit based on the output of the volumetric sensor are provided, and the control omission is as follows: a first cuff pressure detection means for detecting a first cuff pressure P _c1 at which the volume pulse wave amplitude of the volume sensor output is maximum; and applying a second cuff pressure P _c2 lower than the first cuff pressure P _c1 to the cuff; In this state, the average value of the volume sensor output is set as a servo target value, and the pressure control means is servo-controlled so that the volume pulse wave amplitude is minimized based on the volume sensor output signal, and the volume pulse wave amplitude is two-cuff pressure detection means that continuously detects the cuff pressure at which the second cuff pressure becomes equal to or less than a predetermined value;
A non-invasive continuous sphygmomanometer characterized by comprising blood pressure calculation means that calculates the measured blood pressure value as the sum of the value obtained by subtracting the second cuff pressure P _c2 from the cuff pressure P _c1 . 2. The non-invasive continuous blood pressure monitor according to claim 1, wherein the second cuff pressure P _c2 is a constant pressure lower than the first cuff pressure P _c1 . 3. The non-invasive continuous method according to claim 1, wherein the second cuff pressure P _c2 is a cuff pressure at which the volume pulse wave amplitude becomes approximately 1/2 of the maximum value. Sphygmomanometer.