JPH071273B2 - Method for measuring oxygen saturation of hemoglobin and reflected light sensor used therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a measuring method for irradiating a subject with light having a red wavelength and light having a near-infrared wavelength and measuring the hemoglobin oxygen saturation by the reflected light intensity. And a reflected light sensor used therefor.

[Prior art and its problems]

Conventionally, as a method of measuring hemoglobin oxygen saturation in blood, the collected blood or tissue is irradiated with red light and near-infrared light and its reflected light intensities Er and Eir are measured, and this is substituted into the following equation. It is known how to ask.

This utilizes the fact that even if the oxygenation state of hemoglobin changes, the light absorption of near-infrared light with a wavelength of 805 ± 15 nm hardly changes, and the hemoglobin oxygen saturation HbOS
Where HbOS = A + B (Eir / Er) A, B: physiological factors of blood and coefficients resulting from sensor characteristics.

According to this formula, it can be seen that the reflected light intensity ratio (Eir / Er) and the hemoglobin oxygen saturation HbOS have a linear relationship (linear relationship), but in reality, the reflected light intensity ratio (Eir / Er) and hemoglobin It is experimentally confirmed that the oxygen saturation HbOS does not have a perfect linear relationship as shown by the chain line in Fig. 6, and the reflected light intensity is affected by the volume ratio (hematcrit) of blood cells contained in blood. ing.

That is, the reflected light intensity changes depending on the degree to which the light irradiated to blood is scattered at the boundary between red blood cells and plasma. Therefore, if the hematocrit of the subject changes, the reflected light intensity also changes accordingly.

So, for example, hematocrit H = 30,35,40,45
As it changes with (%), the relationship between the reflected light intensity ratio (Eir / Er) and the hemoglobin oxygen saturation HbOS changes as shown by the chain line in Fig. 6, and it is necessary to accurately measure the hemoglobin oxygen saturation HbOS. At the same time, the hematocrit of the subject must be measured, and the values of the coefficients A and B in the above equation must be determined accordingly.

However, it is very difficult to determine the coefficients A and B according to the value of the hematocrit of the subject in this way, and even if they are determined, the reflected light intensity ratio (Eir / Er) and the hemoglobin oxygen saturation level are determined. Since it is not in a completely linear relationship with HbOS, an error will occur as long as the hemoglobin oxygen saturation HbOS is obtained by the conventional method, and it is difficult to measure it accurately.

Further, in the case of measuring the reflected light intensity, the conventional sensor has a sensor portion including a light emitting element and a light receiving element, and a preamplifier for amplifying an output from the light receiving element, which are integrally formed on the same substrate. In addition to being unable to downsize, it was uneconomical to replace the entire preamplifier when the sensor unit failed.

In addition, since the periphery of the sensor is open, it is easy for light to enter from the outside to pick up noise, and since the distance between the light emitting element and the light receiving element is not constant, the reflected light intensity of red light and near infrared light can be adjusted under the same conditions. It had the drawback that it could not be measured.

[Object of the Invention] Accordingly, it is an object of the first invention of the present application to provide a hemoglobin oxygen saturation measuring method capable of accurately measuring hemoglobin oxygen saturation without being affected by hematocrit.

The second invention of the present application is a reflected light sensor used in the method for measuring oxygen saturation of hemoglobin, which is less susceptible to noise due to external light, and has the same reflected light intensity of red light and near infrared light. It is an object of the present invention to provide a low-cost and small reflected light sensor which can be measured by, and at the same time, has only the sensor unit independent.

[Structure of Invention]

In order to achieve this object, the first invention of the present application is to irradiate a subject such as collected blood or tissue with red light and near-infrared light, and the reflected light intensity of each light causes hemoglobin oxygen of the subject. In the hemoglobin oxygen saturation measuring method for determining the saturation, the reflected light intensities of red light and near infrared light are Er and
Eir, and the hemoglobin oxygen saturation HbOS is obtained by the formula: HbOS = A + B [Eir / (Er + C)] A, B: coefficient due to physiological factors of blood and characteristics of sensor C: correction coefficient .

Further, the second invention of the present application, the reflected light intensity of each light by irradiating the subject with red light and near-infrared light in order to measure the hemoglobin oxygen saturation of the subject such as collected blood or tissue. A reflected light sensor for detecting, wherein at least two light emitting elements for outputting red light and near infrared light are contained in a small container whose periphery is shielded and whose upper surface is transparently formed as a subject contact surface, and the subject. A light receiving element that detects the reflected light intensity of red light and near infrared light radiated to the subject on the contact surface is arranged at equal intervals through a shield plate, and a connection terminal fixed to the container is provided. It is characterized in that it is adapted to be connected to the measuring device through.

[Operation of the invention]

According to the first invention of the present application, the hemoglobin oxygen saturation HbOS
Since the corrected reflected light intensity ratio [Eir / (Er + C)] can be approximated by a substantially perfect linear relationship regardless of the hematocrit value, it is possible to accurately measure the reflected light intensities Er and Eir. The hemoglobin oxygen saturation HbOS can be obtained.

Further, according to the second invention of the present application, the light-emitting element and the light-receiving element for red light and near-infrared light are evenly spaced in a small container in which the periphery is shielded and only the upper surface is transparently formed as the subject contact surface. Since it is installed, it is not affected by external light, and at the same time, the reflected light intensity of red light and near infrared light can be measured under the same conditions. Since it is designed to be connected to the device, replacement of the sensor due to a failure or the like can be performed very easily and quickly.

[Examples] Hereinafter, the present invention will be specifically described based on Examples shown in the drawings.

FIG. 1 is a plan view showing an example of a reflected light sensor for measuring hemoglobin oxygen saturation according to the present invention, and FIG. 2 is a sectional view seen from the side.

In the figure, S is a reflected light sensor. For example, in a casing (small container) 1 formed by cutting off the head of a TO-5 can used for an operational amplifier, light emitting diodes (light emitting elements) 2, 3 and 4 and a photodiode (light receiving element) 5 are mounted on a substrate 6 with their light emitting surface and light receiving surface facing upward, and a shielding plate is provided between the light emitting diodes 2, 3 and 4 and the photodiode 5. 7 are provided.

A transparent epoxy resin 8 is filled in the casing 1, the head surface is polished, and the surface is covered with transparent polyurethane having excellent antithrombogenicity to form a subject contact surface 9.

The inner surface of the casing 1 is finished in black in order to minimize the generation of noise due to the reflection of the output light of the light emitting diodes 2, 3 and 4.

The light emitting diodes 2, 3 and 4 have output light wavelengths of 665 nm (red light), 795 nm (near infrared light) and 910 nm, respectively.
It is selected as (infrared light) and is arranged on the circumference of a radius of about 3 mm centering on the Hoy diode 5 so as not to cause an error in reflected light intensity due to a difference in distance.

This distance (3 mm) is sufficient for the output light from the light-emitting diodes 2, 3 and 4 to be scattered by the red blood cells of the subject contacting the subject contact surface 9 and diffused before being detected by the light receiving element 5. It was selected as a proper distance.

Further, the light emitting diodes 2, 3 and 4 are adapted to be sequentially blinked by being supplied with current from pins (connection terminals) P2, P3 and P4, respectively, and their ground sides are connected to the pins P1 and P5.

The photodiode 5 has a bias voltage (-12
V) is supplied, the reflected light intensity E is output from the pin P6, and the dark current and the leakage current are supplied to the pin P7.
It is grounded to reduce noise during measurement.

FIG. 3 shows the light emitting diodes 2, 3 and 4 of the reflected light sensor S.
Are sequentially emitted and the output from the photodiode 5 is individually taken out in synchronism with the light receiving elements 2, 3 and 4, and a block diagram showing a measuring device K is shown in FIG. It is an explanatory view shown.

Reference numeral 11 is a reference pulse generator for generating a reference pulse KP for blinking the light emitting diodes 2, 3 and 4 and having a frequency of
A reference pulse KP having a pulse width of 20 μs and a frequency of 2 KHz (0.5 ms) is supplied to the drive pulse generator 12.

In the drive pulse generator 12, the light emitting diodes 2, 3 and 4 are
Three kinds of drive pulses D1, D2, and D3 with a phase difference of 40 μs are output in order to sequentially blink at 0 μs intervals,
Each drive pulse corresponds to a light emitting diode drive device 13, 14 and 1 respectively.
Is supplied to the pins P2, P3 and P4 of the reflected light sensor S via 5, and the respective light emitting diodes 2, 3 and 4 are driven by the drive pulses D1 and D2.
And it blinks sequentially according to D3.

The reflected light intensity E detected by the photodiode 5 in response to the blinking of the light emitting diodes 2, 3 and 4 is output from the pin P6 of the sensor S, and the preamplifier 16 and the main amplifier 17 are provided.
Amplified through and supplied to detectors 18, 19 and 20.

At this time, since the reflected light intensity of each wavelength is output together from the pin P6, it is necessary to detect this individually for each wavelength.

Therefore, the drive pulses D1, D2 and D3 output from the drive pulse generator 12 are input to the detection pulse generator 21 and the detection pulses S1, S2 and S3 having a pulse width of 2 μs are respectively detected by the detectors 18, 19 and 20. To the detection pulses S1, S2 and S3, and by detecting only the reflected light intensity, the reflected light intensity for each wavelength can be detected.

The reflected light intensities measured by the detectors 18, 19 and 20 are input to the microcomputer 23 via the A / D converter 22 ...

The microcomputer 23 includes at least an interface circuit 24, an arithmetic processing device 25, and a storage device 26,
A predetermined calculation process is executed based on the measured reflected light intensity to calculate the hemoglobin oxygen saturation HbOS.

FIG. 5 is a flow chart showing the processing procedure of the arithmetic processing unit 25. When the measurement is started, the processing shown in FIG. 5 is started to be executed. First, in step (1), the detectors 18, 19 and 20 are operated. The reflected light intensity of each wavelength input via the A / D converter 22 is stored in a predetermined storage area of the storage device, and, for example, when each 20 samples are measured, the process proceeds to step (2).

In step (2), red light (665 nm) and near infrared light (7
The average value of the reflected light intensities Er and Eir of (95 nm) is obtained, and the process proceeds to step (3). The hemoglobin oxygen saturation HbOS is calculated based on a predetermined formula programmed in advance, and the result is obtained in step (4). Is output.

The above is an example of the configuration of the reflected light sensor S for measuring the hemoglobin oxygen saturation according to the present invention, and its operation and the hemoglobin oxygen saturation measuring method will be described.

According to the present invention, since the relationship between the hemoglobin oxygen saturation HbOS and the reflected light intensities Er and Eir is expressed by HbOS = A + B [Eir / (Er + C)], each of the reflected light sensors S used for measurement is first described. It is necessary to obtain the coefficients A, B and C in advance. Coefficient A, B
To determine C and C, the reflected light intensities Eir and Er are measured synchronously while changing the hemoglobin oxygen saturation HbOS.
The coefficients A, B and C can be obtained by the first-order approximation method.

At this time, the hemoglobin oxygen saturation HbOS is measured by another conventionally known method.

Substituting the coefficients A, B, and C obtained in this way into the previous equation, the previous equation can be expressed by, for example, HbOS = 1.145−0.34 [Eir / (Er + 0.08)],
This formula is programmed in the microcomputer 23.

Since the coefficients A, B and C do not change due to hematocrit, it is not necessary to correct their values if they are obtained first.

Then, in order to measure the hemoglobin oxygen saturation HbOS using the reflected light sensor S, first, the pins P1 to P8 of the reflected light sensor S are connected to the connector (not shown) of the measuring device K and measurement is possible. Leave it in a state.

Next, when the measuring device K is turned on by dropping the collected blood on the subject contact surface 9 or placing a skin tissue or the like, the light emitting diodes 2, 3 and 4 of the reflected light sensor S drive pulses D1, D2 and
At the same time as the subject is illuminated with red light and near-infrared light by being blinked sequentially by D3, the intensity of reflected light of each wavelength is measured by the photodiode 5, and the A / D converter 2 for each wavelength is measured.
It is converted into a digital signal via 2 and stored in a predetermined storage area of the storage device 26 (step (1)).

At this time, the periphery of the reflected light sensor S is shielded by the casing 1, and the transparent subject contact surface 9 formed on the upper surface is covered with the subject such as blood, so that other light enters from the outside. And thus not picking up noise.

Then, the measurement is stopped when 20 samples are measured for each wavelength, and the arithmetic processing unit 25 obtains the average value of the reflected light intensities Er and Eir of the red light (665 nm) and the near infrared light (795 nm) (step (2 )), The average value is substituted into the following equation to obtain the hemoglobin oxygen saturation HbOS (step (3)).

HbOS = 1.145-0.34 (Eir / (Er + 0.08)] The relationship between the hemoglobin oxygen saturation HbOS obtained by this formula and the corrected reflected light intensity ratio [Eir / (Er + C)] is the sixth.
As shown by the solid line in the figure, it has been experimentally proved that there is a nearly perfect linear relationship (linear relationship) regardless of the value of hematocrit.

That is, according to the conventional method, the hemoglobin oxygen saturation HbOS
Is represented by, for example, HbOS = 0.97−0.158 (Er / Eir), and the error is 8.98%, while the error determined by the present invention is significantly reduced to 1.77%.

Therefore, according to the method of the present invention, only by measuring the reflected light intensity, the hemoglobin oxygen saturation of the subject can be measured very accurately.
HbOS can be calculated.

Further, the reflected light intensity Eir of near infrared light (795 nm) and the hemoglobin concentration [Hb] can be expressed by [Hb] = aEir ² + bEir + C a, b, c: a coefficient due to the characteristics of the reflected light sensor. For example, since the reflected light sensor S has a relationship of [Hb] = 0.445Eir ² −7.14Eir + 35.7, the hemoglobin concentration [Hb] of the blood sampled can be obtained from the equation.

Then, from this hemoglobin concentration [Hb] and the hemoglobin oxygen saturation HbOS, the oxygen concentration [O2] contained in the blood can be obtained by [O2] = 1.34 × HbOS × [Hb].

As described above, according to the reflected light sensor S of the present invention, infrared light (660 nm) and near-infrared light (795 nm) are radiated to the object in contact with the object contact surface 9 and the intensity of the irradiation light is increased. Er and E
ir can be measured, and from these values, the hemoglobin oxygen saturation HbOS, hemoglobin concentration [Hb] and blood oxygen content [O2] can be measured.

〔The invention's effect〕

As described above, according to the first aspect of the present invention, the hemoglobin oxygen saturation HbOS and the corrected reflected light intensity ratio [Eir / (Er +
C)] and can be expressed by a substantially perfect linear relationship regardless of the value of hematocrit, the hemoglobin oxygen saturation HbOS can be calculated extremely accurately from the reflected light intensities of the red light and the near infrared light. Hemoglobin oxygen saturation
Since there is no need to measure the value of hematocrit in the measurement of HbOS and consider it, the hemoglobin oxygen saturation
HbOS can be measured easily and accurately.

Further, according to the second invention of the present application, the light-emitting element and the light-receiving element for red light and near-infrared light are arranged in a small container in which the periphery is shielded and only the upper surface is transparently formed as the subject contact surface. In addition, since the distance between each light emitting element and the light receiving element is kept constant, it is possible to prevent the generation of noise while being less affected by the light from the outside, and at the same time,
It has an excellent effect that it is possible to measure the reflected light intensities of red light and near infrared light under the same conditions, and a reflected light sensor is formed only with a light emitting element and a light receiving element and a measuring device via a connection terminal. Since the connection is made, the sensor can be downsized and the unit price can be reduced, and even if the reflected light sensor should fail, it can be replaced easily and quickly.

[Brief description of drawings]

FIG. 1 is a plan view showing a reflected light sensor according to the present invention, and FIG.
FIG. 3 is a cross-sectional view as seen from the side, FIG. 3 is a block diagram showing a reflected light sensor driving device, FIG. 4 is an explanatory diagram showing its signal waveform, and FIG. 5 is a flow chart showing the processing procedure of a microcomputer. FIG. 6 is an explanatory diagram showing the correlation between the reflected light intensity ratio and the hemoglobin oxygen saturation HbOS. Explanation of symbols S ... Reflected light sensor, 1 ... Casing, 2,3,4 ... Light emitting diode (light emitting element), 5 ... Photodiode (light receiving element), 7 ... Shielding plate, 8 ... Transparent epoxy resin , 9
…… Subject contact surface, P1 to P8 …… Pin (connection terminal), K…
… Measuring device, 11 …… Reference pulse generator, 12 …… Drive pulse generator, 18,19,20 …… Detecting device, 23 …… Microcomputer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 49-69391 (JP, A) JP 50-143380 (JP, A) JP 51-45488 (JP, A) Actual 47- 35283 (JP, U) Actually opened Sho 47-18588 (JP, U) Japanese Patent 42-20592 (JP, B1) Japanese Patent 51-16797 (JP, B2)

Claims (2)

[Claims] 1. A hemoglobin oxygen saturation measuring method for irradiating a sample such as collected blood or tissue with red light and near-infrared light and obtaining the hemoglobin oxygen saturation of the sample by the reflected light intensity of each light. , The reflected light intensity of red light and near infrared light is Er and Eir, and the hemoglobin oxygen saturation H
A method for measuring hemoglobin oxygen saturation, characterized in that bOS is calculated from the equation: HbOS = A + B [Eir / (Er + C)] A, B: physiological factors of blood and sensor characteristics C: correction coefficient . 2. Reflection for irradiating the subject with red light and near-infrared light to measure the hemoglobin oxygen saturation of the subject such as collected blood or tissue, and detecting the reflected light intensity of each light. An optical sensor, at least two light-emitting elements for outputting red light and near-infrared light in a small container whose periphery is shielded and whose upper surface is transparently formed as a subject contact surface, and on the subject contact surface The light receiving elements for detecting the reflected light intensities of the red light and the near-infrared light radiated to the subject are arranged at equal intervals through the shield plate, and measured through the connection terminals fixed to the container. A reflected light sensor for measuring hemoglobin oxygen saturation, which is adapted to be connected to a device.