JPH10216115A - Highly accurate reflection type degree of oxygen saturation measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type degree of oxygen saturation measuring apparatus with a higher measuring accuracy. SOLUTION: The interval between a first light emitting element 18 and a second light emitting element 20 and a photodetector 16, namely, the radius (r) is set 5-7mm. Hence, back scattered light detected by the photo-detector 16 is made larger in proportion at a part larger in depth from the surface of a body, namely, a part higher in the density of a blood capillary. A larger ratio (ACR/DCR) or (ACIR/DCIR) between an AC component ACIR or ACR and a DC component DCR or DCIR reduces effect of noises. Moreover, a proper intensity of the first signal SVR and the second signal SVIR obtained achieves a sufficient stability and accuracy in the measurement of the degree of oxygen saturation SaO2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type oxygen saturation measuring device for measuring the oxygen saturation of arterial blood of a living body.

[0002]

2. Description of the Related Art A light source for emitting light of a first wavelength and a second wavelength toward a living tissue, and a backscattered light of a first wavelength and a backscattered light of a second wavelength scattered in the living tissue, respectively. Detecting the backscattered light of the first wavelength and the second
A first optical signal and a second optical signal respectively representing backscattered light of a wavelength.
An oxygen saturation measuring device comprising an optical sensor that outputs an optical signal and determining the oxygen saturation of arterial blood of a living body based on the ratio between the AC component and the DC component in the first optical signal and the second optical signal is proposed. Have been. For example, JP-A-63-
This is the reflection type oxygen saturation measurement device described in Japanese Patent No. 92335. According to this, it is possible to continuously measure the oxygen saturation without performing the ischemic operation.

[0003]

In the conventional reflection-type oxygen saturation measurement, a light source that emits light toward the body surface of a living body and a light source that is reflected inside the body surface and then travels backward from the body surface. In general, the distance from the optical sensor that receives the backscattered light is set to, for example, about 3 mm. However, the distance between the light source and the optical sensor is 3mm
From the setting of the degree, in the backscattered light detected by the optical sensor, the ratio of the scattered light from the part close to the epidermis where the depth from the body surface is shallow, that is, the density of the capillaries is low, is increased. Therefore, the ratio between the AC component and the DC component of the optical signal output from the optical sensor is reduced, and the influence of noise is increased. Thus, there is an inconvenience that the measurement accuracy of the oxygen saturation cannot be sufficiently obtained.

On the other hand, in order to increase the proportion of scattered light from a part deep from the body surface, that is, a part having a high density of capillary blood vessels, of the backscattered light detected by the optical sensor, When the distance between the optical sensor and the optical sensor is increased, the ratio of the AC component to the DC component of the optical signal output from the optical sensor increases, but the intensity of the optical signal decreases exponentially. However, there is a disadvantage that the accuracy becomes unstable and sufficient accuracy cannot be obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a reflection type oxygen saturation measuring device having high measurement accuracy.

The present inventors have conducted various studies on the background of the above circumstances, and as a result, as the distance between the light source and the optical sensor increases, the ratio of the AC component to the DC component of the optical signal output from the optical sensor increases. Is larger, but has a characteristic of decreasing when the distance exceeds about 7 mm. On the other hand, the optical signal decreases exponentially as the distance increases, so that when the distance is set in the range of 5 to 7 mm, the AC component and the DC We have found that the ratio between the components and the intensity of the optical signal can be sufficiently obtained.

[0007]

The present invention has been made based on the above findings, and the gist of the invention is as follows.
A light source that emits light of the first wavelength and the second wavelength toward the living tissue; and a backscattered light of the first wavelength and a backscattered light of the second wavelength that are scattered in the living tissue. An optical sensor that outputs a first optical signal and a second optical signal that respectively represent the backscattered light of one wavelength and the backscattered light of the second wavelength; and an AC component and a DC in the first optical signal and the second optical signal. In a reflection type oxygen saturation measuring device for determining the oxygen saturation of arterial blood of a living body based on the ratio of the components, the distance between the light source and the optical sensor is set to 5 to 7
mm.

[0008]

As described above, since the distance between the light source and the optical sensor is set to 5 to 7 mm, a portion of the backscattered light detected by the optical sensor which has a deeper depth from the body surface, that is, Since the ratio of the scattered light from the portion where the density of the capillaries is high is increased, the ratio between the AC component and the DC component of the optical signal output from the optical sensor is increased, and the influence of noise is reduced. Is obtained, and the stability and accuracy of the oxygen saturation measurement are sufficiently obtained.

[0009]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a configuration of a reflection type oximeter provided with a reflection type probe, that is, an oxygen saturation measuring device. In FIG. 1, a reflective probe 10 is a body surface 1 such as a forehead or a finger having a relatively high density of peripheral blood vessels of a living body.
2 is attached in a state of being in close contact. This reflection type probe 1
Reference numeral 0 denotes a relatively shallow bottomed cylindrical housing 14 and a central portion of the bottom inner surface of the housing 14 for detecting backscattered light that is scattered within the body surface 12 and emerges toward the light source. And a plurality of light-receiving elements 16 comprising LEDs and the like, which are alternately provided at predetermined intervals on a circumference of the same radius r centered on the light-receiving elements 16 on the bottom inner surface of the housing 14 and a light-receiving element 16 comprising a photodiode or a phototransistor. (Eight in this embodiment) of the first light emitting element 18 and the second light emitting element 18
A light-emitting element 20; a transparent resin 22 provided integrally with the housing 14 to cover the light-receiving element 16 and the light-emitting elements 18 and 20 to protect the light-emitting element 20; And the body surface 1 of light emitted from the light emitting elements 18 and 20
An annular light-shielding wall 24 that shields reflected light from inside 2 toward the light-receiving element 16 is provided.

The first light emitting element 18 has a first wavelength λ.₁And
For example, it emits red light having a wavelength of about 730 nm, and emits second light.
The element 20 has the second wavelength λ_TwoFor example, a wavelength of about 880 nm
Which emits infrared light. In FIG. 2, one-dot chain
Line is the extinction coefficient of oxygenated hemoglobin (oxy-hemoglobin)
And the solid line shows deoxy-hemoglob.
In) shows the extinction coefficient. The first wavelength λ₁Is an acid
Extinction coefficient between oxyhemoglobin and anoxic hemoglobin
The region where the difference is larger than a predetermined value, that is,
The value within the short wavelength range and set as high as possible
The second wavelength λ_TwoIs oxygenated hemoglobin
Absorption coefficient difference from anoxic hemoglobin is smaller than the specified value
Area, that is, the area on the wavelength side longer than 800 nm
Value and set as low as possible. In addition, above
The first wavelength λ₁And the second wavelength λ _TwoAre not necessarily
Is not limited to the wavelength of oxygenated hemoglobin
Extinction coefficient of anoxic hemoglobin is large
Wavelengths that differ greatly from each other and wavelengths at which both extinction coefficients are approximately the same
Should be fine.

The first light emitting element 18 functioning as a light source
And the second light emitting element 20 are alternately driven by the drive circuit 54.
The first light emitting element 18 and the second light emitting element 18
Biological tissue (blood vessel) just below the body surface 12 from the two light emitting elements 20
The first wavelength λ towards the floor)₁Light and the second wavelength λ_Twoof
When light is emitted alternately, the blood in the blood capillaries of living tissue
Backscattered light scattered by the contained blood cells is reflected
As it comes out of the body surface 12 as light, its backscattered light
That is, the reflected light from the living tissue (the vascular bed)
Each light is received by the light receiving element 16 functioning as a sensor
And the first wavelength λ ₁Optical signal SV indicating the scattered light of_RYou
And the second wavelength λ_TwoOptical signal SV indicating the scattered light of_IRComes out
It is being forced.

FIG. 3 is a view of the housing 14 of the reflective probe 10 as seen from the surface facing the body surface 12. A light receiving element 16 is disposed at the center of the housing 14, the annular light shielding wall 24 is fixed at a concentric position, and a plurality of first light emitting elements 18 and second light emitting elements 20 Outside the light-shielding wall 24,
They are alternately arranged along a concentric circle having a radius r shown by a dashed line.

The radius r is defined by the light receiving element 16 and the first light emitting element.
Showing the center distance between the element 18 and the second light emitting element 20
It is. In theory, the light receiving element 16 and the first light emission
The half indicating the center distance between the element 18 and the second light emitting element 20
The larger the diameter r, the longer the backscattered light path becomes
Receiving the first optical signal SV_RAlternation of
Component ratio (AC / DC)_RAnd the second optical signal SV_IRAlternation of
Component ratio (AC / DC) _IRIs thought to be larger,
According to experiments performed by the present inventors, as shown in FIG.
Is more than 7mm, AC / DC component ratio (AC / DC)_Rand
(AC / DC) _IRAnd the effect of noise increases.
Measurement accuracy. Also, the radius r
Becomes larger, the backward scattering detected by the light receiving element 16 increases.
The cause of the instability of the measurement is that the scattered light attenuates exponentially.
Become. For this reason, in the past it was set to about 3 mm.
By setting the radius r in the range of 5 to 7 mm,
AC / DC component ratio (AC / DC)_RAnd (AC / DC)_IRTo
The effect of noise on the
Is obtained and detected by the light receiving element 16.
The gain of the backscattered light is sufficient to obtain a stable measurement.
Can be FIG. 4 shows the three-dimensional photon diffusion theoretical formula (number
Using 1), the distance r from the light source_aScattering at the position
Light intensity I_ref(R_aAlso proved by asking
It is.

[0015]

## EQU1 ## I _ref (r _a ) = (2 / d) [μ _s / (μ _s +
μ _a )] ΣΔA _n [1-e ^{-d / d0} (-1) ⁿ ] [1-
_{(2r a) / b · k} 1 (γ n b) I 1 (γ n r a) ], however, I _ref (r _a) = backscattered light in the radius r _a (reflected light), d is the thickness of the medium , Μ _s is the scattering coefficient of the medium, μ _a is the absorption coefficient of the medium, _An is the coefficient, d ₀ is the penetration distance of the incident light into the medium, b is the radius of the light source, k ₁ and I ₁ are Bessel functions, γ _n is an eigenvalue, and n is an integer.

First light emitting element 18 and second light emitting element 20
Are alternately emitted at a relatively high frequency of about several hundred Hz to several kHz for a certain period of time.
Is the first optical signal SV _R indicating the backscattered light of the first wavelength λ ₁
An optical signal SV including the second optical signal SV _IR indicating the backscattered light having the second wavelength λ ₂ is output to the low-pass filter 32 via the amplifier 30. The low-pass filter 32 removes noise having a frequency higher than the frequency of the pulse wave from the input optical signal SV, and outputs the optical signal SV from which the noise has been removed to the demultiplexer 34. The above first optical signal S
V _R and the second optical signal SV _IR change in synchronization with the pulse, for example, as shown in FIG.

The demultiplexer 34 outputs a switching signal S to be described later.
C, the first light emitting element 18 and the second light emitting element 20 are switched in synchronization with the light emission, so that the first wavelength λ ₁
First optical signal SV _R sample and hold circuit 36 and A / D converter 38 via the arithmetic control circuit 3 is a red light
9 to the I / O port 40, and the second
The second optical signal SV _IR , which is infrared light of wavelength λ ₂ , is transmitted to the I / O via the sample and hold circuit 42 and the A / D converter 44.
Supply sequentially to port 40. Sample hold circuit 3
6, 42 convert the input optical signals SV _R and SV _IR into A / D
When sequentially outputting to the converters 38 and 44, the A / D converters 38 and 44 for the previously output optical signals SV _R and SV _IR
The optical signals SV _R and SV _IR to be outputted next are respectively held until the conversion operation in is completed.

The first optical signal SV _R and the second optical signal S
V _IR not only changes periodically in synchronization with the pulse,
As shown in FIG. 5, a relatively long cycle swell fluctuation synchronized with the respiration cycle T _RE is included. When the blood pressure value changes in synchronization with the respiratory cycle T _RE , the blood volume in the capillary in the living tissue changes in synchronization with the respiratory cycle T _RE , so that the blood cell in the capillary scatters blood. The received first optical signal SV _R and second optical signal SV _IR also have their respiratory cycle T _RE.
It is thought that it will receive a change synchronized with. The respiratory cycle T
_RE is generally about 3 to 5 times the pulse cycle and about 4 times as much.

The I / O port 40 is connected to a CPU 46, a ROM 48, a RAM 50, and a display 52 via data bus lines. The CPU 46 sets the RA
Using the storage function of M50, the measuring operation is executed in accordance with a program stored in the ROM 48 in advance, and a command signal SLD is output from the I / O port 40 to the drive circuit 54 to output the first light emitting element 18 and the second light emitting element 20. Alternately emit light at a relatively high frequency of about several hundred Hz to several kHz for a certain period of time, and output a switching signal SC in synchronization with the light emission of the first light emitting element 18 and the second light emitting element 20 to perform demultiplexing. 34, the first optical signal SVR is _sent to the sample-and-hold circuit 36 and the second optical signal SVR is
V _IR is distributed to the sample and hold circuit 42. Further, the CPU 46 determines the oxygen saturation in the blood flowing through the peripheral blood vessels based on the photoplethysmographic waveforms represented by the first optical signal SV _R and the second optical signal SV _IR according to a program stored in advance, and the determination. The displayed oxygen saturation SaO2 is displayed on the display 52.

Here, in this embodiment, a cap-shaped rubber member 56 is further provided integrally with the housing 14 so as to cover the outer peripheral surface and the bottom outer surface of the housing 14. The rubber member 56 is formed in a sponge shape using, for example, chloroprene rubber or the like as a raw rubber, and has a suitable heat insulating property. Then, a portion of the rubber member 56 located on the outer peripheral side of the housing 14 is fixed to the body surface 12 via the double-sided adhesive sheet 58, so that the opening end surface of the housing 14 and the light shielding member 24
The probe 10 is mounted on the body surface 12 such that the distal end surface of the probe 10 is in close contact with the body surface 12. In FIG. 1, the double-sided pressure-sensitive adhesive sheet 58 is drawn much thicker than it is for convenience.

FIG. 6 is a functional block diagram for explaining a main part of the control function of the arithmetic control circuit 39. In FIG. 6, the frequency analysis means 70 performs a frequency analysis using the fast Fourier transform method for each predetermined section, so that the first optical signal SV output from the light receiving element 16 is obtained.
_R and the second optical signal SV _IR from the first
Optical signal SV _R alternating current component AC _R and DC component _R and an AC component of the second optical signal SV _IR AC _IR and DC component of
_IR and each are sequentially determined. Since the first optical signal SV _R and the second optical signal SV _IR are changed in synchronization with the pulsation synchronized with the heartbeat of the blood volume in the capillary of the living tissue, the AC components AC _R and AC _IR are It is obtained as a signal power (watt) of a frequency component corresponding to the pulse rate PR (1 / min) of the living body, that is, a pulse frequency PF (Hz), and the DC components DC _R and DC _IR are signals of a frequency component corresponding to DC. Obtained as power (watts). In FIG.
An example of the frequency spectrum of the first optical signal SV _R or the second optical signal SV _IR obtained by the above frequency analysis is shown.

The section in which the frequency analysis is performed by the frequency analysis means 70 is an integral multiple of a half cycle or one cycle of the respiratory cycle T _RE of the living body to be measured, for example, an integral multiple of a time twice or four times the pulse cycle. Set to time. It is known that the arterial blood pressure fluctuates in synchronism with the respiratory cycle, whereby the blood volume in the capillaries of the living tissue pulsates in synchronism with the pulse and causes swelling in synchronism with the respiratory cycle. since, the first optical signal SV _R and the second optical signal SV
_{Since the IR} also undergoes fluctuation synchronized with the respiratory cycle, in the above-described manner, the signals in the section are averaged, and at least the effect of the respiratory fluctuation is suitably eliminated.

[0023] AC to DC component ratio calculating means 72, the first optical signal SV _R of the alternating current component AC _R and the direct current component DC _R and alternating current component AC _IR and DC of the second optical signal SV _IR determined by the frequency analyzing means 70 From the component _DCIR , an AC / DC component ratio (AC _R / DC _R ) of the first optical signal SV _{R and} an AC / DC component ratio (AC _IR / DC _IR ) of the second optical signal SV _IR are calculated.

The oxygen saturation calculating means 74 is, for example, as shown in FIG.
Is the relationship shown in the preset equation (Equation 2) shown by the solid line
The first optical signal SV_RAC-DC component ratio (AC_R/ DC
_R) And the second optical signal SV_IRAC-DC component ratio (AC_IR/ D
C_IR) And R [= (AC_R/ DC _R) / (AC_IR/ D
C_IR)], The oxygen saturation SaO2 of the living body is calculated
calculate. In the equation (Equation 2), A indicates a slope.
It is a negative constant, and B is a constant indicating the intercept.

[0025]

## EQU2 ## SaO2 = A × R + B

[0026] Here, the wavelength lambda ₁ of the first optical signal SV _R 7
30 nm, and the wavelength λ _{2 of} the second optical signal SV _IR is 8
The reason why the wavelength is set to 80 nm will be described. That is,
The first wavelength λ ₁ is 665 nm and the second wavelength λ ₂ is 880 n
m, 910 nm, or a first optical signal SV _R and the intensity of the second optical signal SV _IR obtained when a 940 nm,
The first optical signal SV _R and the second optical signal SV _IR are calculated using the equation (Equation 1) showing the three-dimensional photon diffusion theory.
When calculating the AC component and a DC component, AC-DC component ratio of the first optical signal SV _R and (AC _R / DC _R) second optical signal S
AC-DC component ratio of V _IR relationship between the ratio R and the oxygen saturation SaO2 of the (AC _IR / DC _IR) may be approximated by a straight line shown by the solid line becomes the specific linear as indicated by a broken line in FIG. 9 Can not. For this reason, in the low region where the oxygen saturation SaO2 is 80% or less, the measurement accuracy is extremely reduced. However, when the first wavelength λ ₁ is 730 nm and the second wavelength λ ₂ is 880 nm, 910 nm, or 940 nm, the result is as shown by the broken line in FIG. 8, and from the above equation (Equation 2) shown by the solid line in FIG. Even in a low region where the oxygen saturation SaO2 is 80% or less, linear approximation can be performed, and high measurement accuracy can be obtained. This is probably because the penetration depths of the first wavelength λ ₁ and the second wavelength λ ₂ are close to each other.

FIG. 10 is a flowchart for explaining a main part of the control operation of the arithmetic control circuit 39. In step S1 in FIG.
Second optical signal SV _IR representative of the first optical signal SV _R and the second wavelength lambda ₂ of the backscattered light representing the backscattered light having a wavelength lambda ₁ is read. Then, "1" is added to the contents of the timer counter CT in S2, in S3, whether the contents of the timer counter CT reaches a preset determination reference time T ₀ or more is determined. This judgment reference time T ₀
Corresponds to a time width of a unit section to be subjected to frequency analysis in S4 described later, and is an integral multiple of a half cycle of the respiratory cycle T _RE , for example, a time of 2 or 4 times the pulse cycle of the living body to be measured. Is set to an integral multiple of.

Initially, the judgment in S3 is denied, so
The first optical signal S is obtained by repeatedly executing S1 and subsequent steps.
V_RAnd the second optical signal SV_IRAre read continuously.
Then, the first optical signals SV_RAnd the second optical signal SV
_IRThe determination of S3 is affirmed while is continuously read.
Then, in S4 corresponding to the frequency analysis means 70,
And the first optical signal SV_RAnd the second light
Signal SV_IRThe frequency analysis process is executed for each
As a result, the first optical signal SV_RAC component of _R(Shin
Signal power value) and DC component DC_R(Signal power value)
2 optical signal SV_IRAC component of_IR(Signal power value) and
DC component DC_IR(Signal power value).

[0029] Then, step S5 corresponding to the AC-DC component ratio calculating means 72, the alternating current component AC _R and a DC component DC _R of the first optical signal SV _R extracted in the S4,
The ratio AC _R / DC _{R of} the first optical signal SV _R is calculated, and the second optical signal is obtained from the AC component AC _IR and the DC component DC _{IR of} the second optical signal SV _IR extracted in S4. AC-DC component ratio AC _IR / DC _IR of SV _IR is calculated.

Next, in S6 corresponding to the oxygen saturation calculating means 74, the first optical signal S is obtained from a preset relationship (SaO2 = A × R + B) shown by a solid line in FIG.
V _R of the AC-DC component ratio AC _R / DC _R and the ratio R of the AC to DC component ratio AC _IR / DC _IR of the second optical signal SV _IR [= (AC _R / DC
_R ) / (AC _IR / DC _IR )], the oxygen saturation SaO2 of the living body is calculated.

In S7, the oxygen saturation SaO2 of the living body calculated in S6 is displayed on the display 52, and in S8, the content of the timer counter CT is cleared to "0", and then the present routine ends. Let me
S1 and subsequent steps are executed again.

As described above, according to this embodiment, the distance between the first light emitting element 18 and the second light emitting element 20 and the light receiving element 16, that is, the radius r is set to 5 to 7 mm. The ratio of the scattered light from the part deeper from the body surface, that is, the part with a higher density of capillaries in the backscattered light detected by the sensor is increased, so that the AC component AC of the optical signal output from the optical sensor is increased. Ratio of _R or AC _IR to DC component DC _R or DC _IR (AC _R / DC _R )
Or (AC _IR / DC _IR) and increases are less affected by noise, yet the strength of the first optical signal SV _R and the second optical signal SV _IR also obtained, the stability of the measurement of the oxygen saturation SaO2 and Accuracy is sufficiently obtained.

While the embodiment of the present invention has been described with reference to the drawings, the present invention can be applied to other embodiments.

For example, the reflection type probe 1 of the above embodiment
0, the light emitting elements 18 and 20 are alternately arranged along the circumference of the radius r, so that the light receiving element 16 and the light emitting element 1
The distance between the light-emitting elements 18 and 20 was constant along the eccentric circle or the ellipse centered on the light-receiving element 16 although the distance between the light-emitting elements 18 and 20 was constant.
Are arranged alternately so that the distance between at least the pair of light receiving elements 16 and the light emitting elements 18 and 20 may be 5 to 7 mm.

Further, the reflection type probe 10 of the above-described embodiment is used.
Is a light receiving element 1 provided at a center position of the housing 14.
6 and the light-emitting elements 18 and 20 provided on the outer peripheral side of the light-shielding wall 24 surrounding the light-receiving element 16, but the positions of the light-receiving elements 16 and the light-emitting elements 18 and 20 are The position may be replaced by

Further, in the above-described embodiment, the first light-emitting element 18 and the second light-emitting element 20 are provided so that light beams having different wavelengths are output from each other.
This is not always necessary. For example, the number of the light emitting elements 18 and 20 may be one by one, or a single light emitting element that outputs light having different wavelengths may be used.

In addition, the present invention can be variously modified without departing from the spirit thereof.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an oxygen saturation measuring apparatus according to one embodiment of the present invention.

FIG. 2 shows a first wavelength λ _R used in the embodiment of FIG.
FIG. 5 is a diagram showing the relationship between the second wavelength λ _IR and the extinction coefficients of oxygenated hemoglobin and oxygen-free hemoglobin.

FIG. 3 is a diagram showing a surface facing a body surface of a reflection type probe used in the embodiment of FIG. 1;

A light receiving element of the reflection type probe of FIG. 3. FIG and spacing r between the light emitting element, AC-DC component ratio of the first wavelength lambda _R, and the second wavelength _{λ IR (AC R / DC R} ) and (AC _IR / DC is a diagram showing the relationship between the _IR).

5 is a first optical signal SV _R or a time chart illustrating the second optical signal SV _IR waveform showing the back-scattered light detected by the light receiving element of the reflection type probe of FIG.

FIG. 6 is a functional block diagram for explaining a main part of a control function of the arithmetic control circuit in FIG. 1;

FIG. 7 is a diagram showing a first example analyzed by the frequency analysis means of FIG. 6;
AC component AC _{R of} optical signal SV _R or second optical signal SV _IR
Alternatively, it is a diagram showing AC _IR and DC component DC _R or DC _IR .

FIG. 8 shows that the first wavelength λ _R is 730 nm and the second wavelength λ ₂ is 8
The relationship (dashed line) between the ratio R and the oxygen saturation SaO2 at 80 nm, 910 nm, or 940 nm, and the preset relationship (solid line) used in the oxygen saturation calculation means of FIG. FIG.

FIG. 9 shows that the first wavelength λ _R is 665 nm and the second wavelength λ ₂ is 8
It is a figure which shows the relationship (dashed line) of the ratio R and oxygen saturation SaO2 at 80 nm, 910 nm, or 940 nm, and the approximate straight line of the broken line.

FIG. 10 is a flowchart illustrating a main part of a control operation of the arithmetic and control circuit in FIG. 1;

[Explanation of symbols]

 10: Reflective probe 12: Body surface 16: Light receiving element (light sensor) 18: First light emitting element, 20: Second light emitting element (light source)

Claims (1)

[Claims] 1. A light source that emits light of a first wavelength and a second wavelength toward a living tissue, and a backscattered light of a first wavelength and a second wavelength that are scattered in the living tissue, respectively. An optical sensor for detecting and outputting a first optical signal and a second optical signal representing the backscattered light of the first wavelength and the backscattered light of the second wavelength, respectively, the first optical signal and the second optical signal In the reflection type oxygen saturation measuring device for determining the oxygen saturation of the arterial blood of a living body based on the ratio between the AC component and the DC component, the distance between the light source and the optical sensor is set to 5 to 7 mm. Reflective oxygen saturation measurement device.