JPH0318742A - Instrument for measuring saturation degree of oxygen - Google Patents

Abstract

PURPOSE:To exactly obtain the saturation degree of oxygen without being affected by hematocrit even in a region where the saturation degree of oxygen is low by determining the ratios of the reflected light intensity to the respective wavelengths which are logarithmically converted by a converting device and calculating the saturation degree of oxygen. CONSTITUTION:A measurement is started by a measurement start instruction from an operation section 23 and plural reflected light intensities to the light corresponding to 660nm and 800nm wavelengths of LEDs 141 and 142 to which signal transmission is executed by an optical fiber 105 and signal reception by an optical fiber 106 are inputted. This inputting is executed by inputting the digital signal from an A/D converter 22 in synchronization with the timing signal for inputting of the timing signals 33 and 34 outputted form a pulse timing circuit 12 when these timing signals are inputted. The plural reflected light intensities to the respective wavelengths are inputted in this way and are stored in a RAM 25. The average value of the reflected light intensities thereof is then determined. The ratio of the values of the two wavelengths of the calculated intensities of the reflected light is obtd. and normalized and is further logarithmically converted. The saturation degree of oxygen is calculated and displayed 27.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oxygen saturation measuring device that measures the oxygen saturation of hemoglobin by utilizing the light absorption characteristics of hemoglobin in blood.

[Prior Art] Conventionally, as a method for measuring the oxygen saturation level of hemoglobin in blood, light of two wavelengths λl and I'-2 is irradiated into the blood, and the intensity of the reflected light is measured. Oxygen saturation is determined from the following relational expression.

SOz ”A+BX (I2 /I I) However, It,
Iz is the wavelength λ and the reflected light intensity for the light of circle 2, respectively, and A and B are constants.

[Problems to be Solved by the Invention] However, the method of calculating oxygen saturation using the above relational expression is greatly influenced by physiological factors in the blood, especially the hematocrit value (the percentage of red blood cell volume in the blood). There is a problem in that the measurement accuracy decreases when the oxygen saturation is relatively low. In order to solve such problems, the applicant of the present invention has proposed an oxygen saturation measuring device in which the influence of the hematocrit value is reduced in Japanese Patent Laid-Open No. 64-29738. The present application further improves this.

The present invention has been made in view of the above-mentioned conventional example, and an object of the present invention is to provide an oxygen saturation measurement device that can accurately measure oxygen saturation without being affected by the hematocrit value even in a region of low oxygen saturation. do. [Means for Solving the Problems] In order to achieve the above object, the oxygen saturation measuring device of the present invention has the following configuration. That is, a first light irradiation means irradiates the blood with light of a first wavelength, and a second light irradiation means irradiates the blood with light of a second wavelength different from the first wavelength light.
a light irradiation means; a detection means for detecting the intensity of reflected light from the blood of each of the lights irradiated into the blood by the first and second light irradiation means; It has a converting means for logarithmically converting each of the reflected light intensities for each wavelength, and a calculating means for calculating the oxygen saturation by calculating the ratio of the reflected light intensity for each wavelength logarithmically converted by the converting means.

[Operation] In the above configuration, the blood is irradiated with light of the first wavelength and the second wavelength, and the reflected light intensity from the blood of each of the irradiated lights is detected. Each of the reflected light intensities for each wavelength thus detected is subjected to logarithmic conversion, and the ratio of the reflected light intensities for each wavelength is determined. In this way, oxygen saturation can be calculated by substituting this ratio into the relational expression.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. [Description of Oxygen Saturation Measuring Apparatus (Fig. 1)] Fig. 1 is a block diagram showing a schematic configuration of an oxygen saturation measuring apparatus 10 according to an embodiment. In the figure, reference numeral 11,lla is a probe that is used by being incorporated into an extracorporeal circulation circuit such as an artificial heart-lung circuit, and is used to measure the intensity of light reflected in blood. This probe l1
The details will be described in detail later with reference to FIGS. 2 and 3.
Note that, although here, it is configured with two channels to which two probes 1l are connected, it is of course possible to use only one channel.

12 is a pulse timing circuit which outputs a driving timing signal for the LEDs 14 (141 and 142) to the LED driving circuit 13, and also outputs a timing signal for sampling the reflected light intensity for each wavelength to the sample/hold circuit 18. ing. ]3 is the LED drive circuit,
A timing signal from the pulse timing circuit 12 drives one of the two LEDs 1 4 1 and 142 of the LED 14 to emit light. 14 is a light emitting diode (LED) that can output light with a wavelength of 660 nm and light with a wavelength of 800 nm;
1 (wavelength is 660nm) and LED142 (wavelength is 80nm)
0nm). In this way, the lights of different wavelengths emitted from each LED are combined by an optical coupler and become one
The light is collected into a single optical fiber and sent to the probe 11.

Note that by changing the driving voltage of the LED14, the wavelength of the output light can be changed to 660 nm and 800 nm.
If the LED can be changed between the two, one LED can be used instead.

15 is a connection part that connects the probe l1 and the main body of the device;
The probe 11 and the main body are connected by an optical cable 28. 16 is a part in which a photoelectric conversion section and a pre-amplifier are integrated, which inputs reflected light from the probe 11 and outputs an electric signal corresponding to the intensity of the input light. 17 is a main amplifier, which further amplifies the electrical signal from the photoelectric conversion section 16. The sample and hold circuit 18 receives the timing signal from the pulse timing circuit 12, and samples and holds the analog signal from the main amplifier section 17 in synchronization with the timing signal.

Note that the light of each wavelength emitted from the LED 14 is controlled by a timing signal from the pulse timing circuit 12 so that the light of each wavelength does not overlap with each other in time, so the sample and hold circuit 18 calculates the reflected light intensity for each wavelength. Can be held independently. The signal sampled and held in this manner is outputted to the control section 20 after noise components are filtered by the filter circuit 19 .

In the control section 20, the analog signal from the filter circuit 19 is converted into a digital signal by the A/D converter 22 and input to the CPU circuit 21.

The control unit 20 inputs the timing signals 33, 34 (35, a6) from the pulse timing circuit 12, so that the digital signal input from the A/D converter 22 is reflected from which probe and for which wavelength. It is possible to determine whether the strength is Here, for example, the timing signal 33 (35) indicates the input timing of the reflected light intensity for light with a wavelength of 660 nm, and the timing signal 34 (36) indicates the input timing of the reflected light intensity for light with a wavelength of 800 nm. 21 is a CPU circuit including a microprocessor, etc., which performs control according to a control program and various data stored in ROM 24. 25 is a RAM used as a work area for the CPU circuit and temporarily stores various data.
Reference numeral 23 denotes an operation section, which is operated by an operator and can input instructions for starting measurement and various functions. A display section 27 is driven by the display circuit 26 to display messages to the operator, measurement results, and the like. 28 is an external output circuit for outputting measurement data and the like to an external device such as a printer connected through an external output terminal.

30 is a power supply circuit which inputs ACIOOV and creates various power supply voltages used in the apparatus. 31 is a power supply circuit such as a switching regulator, which outputs various DC voltages as shown in the figure. 32 is a line filter provided on the power line, which attenuates power noise input through the AC line. [Description of the Probe (FIGS. 2 and 3)] FIG. 2 is a diagram showing the shape of the optical sensor probe 11 of the embodiment, and is shown in cross section with a portion cut away for explanation. FIG. 3 is a schematic diagram showing that light emitted from the light irradiation section is reflected by red blood cells and enters the light receiving section.

In FIG. 2, the optical sensor probe 11 is connected to the connector 1.
02, the tube 101 constituting the extracorporeal blood circulation circuit
The inside of the tube 10l is filled with flowing blood. The end surface 103 of the tube 101 is connected to the connector 10
The planar surface is processed to be flush with the inner wall surface 104 of No. 2 to prevent disturbance of blood flow. The sensor probe l1 basically consists of four parts, two of which are PMMA (polymethyl methacrylate).
A probe body 110 that fixes the optical fibers 105 and 106, a fixing nut 107 that fixes the probe body 110 to the connector 102, and the optical fibers 105 and 106.
A soft PVC cap 109 is provided to prevent the connection with the optical sensor probe 1l from having an extremely small curvature, and an O-ring 111 is used to prevent blood from leaking. ing.

Note that quartz fiber may be used instead of PMMA.

The probe 11 of this embodiment includes two optical fibers 10.
5, 106 are fixed, and one of them (105
) uses the aforementioned LED 1 4 to emit light into the blood.
The other optical fiber 106 forms a light irradiation section that transmits light from a light source such as a light source and irradiates the inside of the tube 101. This is an optical fiber that transmits the reflected light to a photoelectric conversion unit l6 such as a photodiode that detects the light intensity. FIG. 3 is a diagram for explaining a state in which light is reflected by red blood cells in blood in the tube 101 in the probe 11 of the embodiment.

In the figure, blood 20 in the tube 101 of the optical fiber 105
Blood 202 is irradiated with light of a specific wavelength from a light irradiation section formed by an end surface that contacts blood 202 . A part of this light reflected by the red blood cells 201 is incident on the light receiving section constituted by the optical fiber 106. This incident reflected light passes through the optical fiber 106 to the photoelectric conversion unit l6.
The reflected light intensity is measured.

The intensity of this reflected light changes by changing the distance 210 between the two optical fibers l○5 and 106. This is because the light propagates through the blood 202 while being repeatedly scattered, and is thought to depend on the path it takes to reach the light receiving section. To explain this simply, the interval (optical fiber 1
When the distance between the centers of fibers 105 and 106) 210 is small, the detected reflected light intensity is
Scattered light from the vicinity of the contact end surface with blood 202 accounts for a large proportion, and as the interval 210 widens, the ratio of scattered light reflected by red blood cells 201 farther from the contact end surface increases.

Therefore, the light emitting optical fiber 105 and the light receiving optical fiber 1
By widening the distance 210 from the inner wall surface 104 of the connector, it becomes less susceptible to disturbances in blood flow and fluctuations in hematocrit that occur near the inner wall surface 104 of the connector. Furthermore, by widening the interval 210, the light is sufficiently diffused, and it becomes possible to receive averaged reflected light that is less affected by the size of individual red blood cells.

In this example, the diameters of optical fibers 105 and 106 are each 0.75 mm, and the spacing between each fiber is approximately 2 mm.
It is said that

[Description of measurement process (Figures 1 and 4)] Figure 4 is a flowchart showing the measurement process executed by the CPU circuit 21 of the oxygen saturation measuring device 10 of the embodiment, and controls the execution of this process. The control program is stored in ROM24.

This process is started, for example, by a measurement start instruction from the operation unit 23, and in step S1, wavelengths of 660 nm and 800 nm are determined.
A plurality of reflected light intensities for light corresponding to m are input. When the timing signals 33 and 34 (or 35, 36) output from the pulse timing circuit 12 are input, the A/D converter 22 is synchronized with the timing signals.
This is done by inputting digital signals from

When a plurality of reflected light intensities for each wavelength are thus inputted and stored in the RAM 25, step. Proceed to S2,
The average value of the reflected light intensity is determined. This is to reduce the influence of errors included in each reflected light intensity information.

Next, the process proceeds to step S3, and the value of the reflected light intensity calculated in step S2 is normalized. The intensity of reflected light from a white plate with a constant reflectance is calculated for each of the wavelengths described above, and is set to W660 and W800, respectively. Then, the reflected light intensity obtained in step S2 is set to R660, respectively.
(Average reflected light intensity for a wavelength of 660 nm). R800
(average reflected light intensity for a wavelength of 800 nm),
The normalized values (Nl, N2) are given by the following formulas.

N, = R660/W660 Na = R 8 0 0 / W 8 0 0 Next, proceed to step S4, and calculate L+ and L2 using the following formula based on the reflected light intensity calculated in the above step. do.

L+ =Lo g {C+ x (N+ 1 C2)
) ・(1) Ll = LO g (c+ x (N2
+c,) ) -(2) However, here C1, C2,
Cs is a constant depending on the optical sensor probe 1l and the blood animal species.

Next, the process proceeds to step S5, and the oxygen saturation is determined using the following formula.

SO2 =ai(L+/Lz)' +az(L+/L*
)2+a+(L+/Lz)+ao − (3) However,
Here ao, a+. a2 and a3 are optical sensor probe 1
1 and blood is a constant that depends on the animal species. In this example, 20 points (5
The oxygen saturation level is calculated by calibrating the average value (measured in seconds) and calibrating the average value. Further, in this example, each of the above-mentioned constants is ao=104.0, at=1 1
．． 08,a2=26.39,as=6.4 0
6, CI=0.6, C2=0.008, and C,=O.

When the oxygen saturation S○2 is calculated in this way, step S6
Then, the calculation result is displayed on the display 27 and the process ends.

In this example, the average value of the reflected light intensity is calculated,
After that, normalization is performed and the oxygen saturation is determined based on the normalized value, but the invention is not limited to this, and the reflected light intensity value input from the A/D converter 22 is directly used. Of course, the oxygen saturation may also be calculated by

FIG. 5 is a diagram showing measurement results measured by the oxygen saturation measuring device 10 of this embodiment.

Here, the optical sensor probe 11 was attached to a blood circuit filled with blood, and the intensity of reflected light was measured. During this measurement, the blood is constantly circulated by a roller bomb, and the oxygen saturation of the blood is controlled by an artificial heart-lung machine installed in the circuit.
To confirm the effect of hematocrit value, hematocrit value was varied from about 20% to 45%.

In the figure, the vertical axis indicates the value measured by ○SM2 HEMOXIMETER■ (manufactured by Radiometer), which spectroscopically measures the oxygen saturation of blood. As explained above, according to this embodiment, even in the low oxygen saturation region of 20 to 40%, where the influence of the conventional hematocrit value could not be eliminated, the reflected light intensity for each of the two wavelengths can be adjusted. By calculating the oxygen saturation using the logarithm of , the oxygen saturation can be accurately measured without being affected by the hematocrit value.

[Effects of the Invention] As explained above, according to the present invention, there is an effect that accurate oxygen saturation can be measured without being affected by the hematocrit value even in a region with low oxygen saturation.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the schematic structure of the oxygen saturation measuring device of the embodiment, Fig. 2 is a diagram showing the structure of the optical sensor probe of the embodiment, and Fig. 3 shows the structure of the light irradiated into blood. A schematic diagram showing how the red blood cells reflect and enter the light receiving unit, Figure 4 is a flowchart showing the measurement process in the oxygen saturation measuring device of the example, and Figure 5 shows the measurement results by the oxygen saturation measuring device of the example. FIG. In the figure, 10... Oxygen saturation measuring device, 1l... Probe, 12... Pulse timing circuit, l3... L
ED drive circuit, l4...LED, 15...connection part,
l6...Photoelectric conversion section, l7...Main amplifier section, 1
8... Sample hold circuit, 19... Filter circuit, 20... Control unit, 21... CPU circuit, 22...
...A/D converter, 23...operation unit, 24...
ROM, 25...RAM, 27...Display, 28.
...Optical fiber, 33-36...Timing signal.

Claims (4)

[Claims] (1) A first light irradiation unit that irradiates blood with light of a first wavelength; and a second light irradiation unit that irradiates light of a second wavelength different from the first wavelength light into the blood. means, a detection means for detecting the intensity of reflected light from the blood of each of the lights irradiated into the blood by the first and second light irradiation means, for each wavelength detected by the detection means. A conversion means for logarithmically converting each of the reflected light intensities; and a calculation means for determining the ratio of the reflected light intensity for each wavelength logarithmically converted by the conversion means and calculating the oxygen saturation using a relational expression. Oxygen saturation measuring device. (2) The conversion means further includes a correction means for correcting the reflected light intensity, and the reflected light intensity corrected by the correction means is logarithmically converted.
The oxygen saturation measuring device described in Section 1. (3) The oxygen saturation measuring device according to claim 1, wherein the first wavelength is 660 nm and the second wavelength is 800 nm. (4) The calculation means calculates logarithmically converted values of reflected light intensity for light with wavelengths of 660 nm and 800 nm, respectively, L_1 and L_1.
_2, then the relational expression a_3(L_1/L_2)^3+a_2(L_1/L_
2) The oxygen saturation measuring device according to claim 3, wherein the oxygen saturation is determined by ^2+a_1(L_1/L_2)+a_0.