JP2014117503A - Degree of oxygen saturation measuring device and degree of oxygen saturation calculation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a degree of oxygen saturation measuring device and a degree of oxygen saturation calculation method capable of calculating a degree of oxygen saturation precisely with only one each of a light incident position and a light detection position.SOLUTION: A degree of oxygen saturation measuring device 1A is a device for measuring a degree of oxygen saturation in a living body, and includes: a light incident part 21 that causes first light and second light whose wavelengths are different from each other to be incident in the living body from one light incident position; a light detection part 22 for detecting the light intensity of the first light and the second light propagated inside the living body at one light detection position; and a CPU 14 for calculating the degree of oxygen saturation in the living body by applying a degree of dimming of the first light and the second light in the living body acquired from the result of the detection by the light detection part 22 to the Modified Beer-Lambert law.

Description

  The present invention relates to an oxygen saturation measuring device and an oxygen saturation calculating method.

  In recent years, methods for non-invasive measurement of oxygen saturation in a living body using near infrared light have been studied. Such methods include spatially resolved spectroscopy (SRS), time resolved spectroscopy (TRS), and phase modulation spectroscopy (PMS).

(1) Spatial resolution spectroscopy (SRS)
After near-infrared light (CW light) is incident on the living body from one light incident position, light absorbed and scattered in the living body is detected at each of the plurality of light detection positions. Then, a common logarithm (attenuation level) of the ratio between the incident light intensity and the detected light intensity at each light detection position is calculated, and oxygen saturation is performed using the gradient of the light attenuation with respect to the distance from the light incident position to the light detection position. Calculate the degree.

(2) Time-resolved spectroscopy (TRS)
Pulse light having an extremely short time width such as several picoseconds is incident on a living body, and a time-resolved waveform of light detected on the surface of the living body is detected by an ultrafast detector. After fitting the time response characteristics of the detected light so as to match the time response characteristics based on the light diffusion theory, the values of the absorption coefficient and equivalent scattering coefficient are obtained, and then the oxyhemoglobin concentration, deoxy The hemoglobin concentration is obtained, and the oxygen saturation is calculated from these.

(3) Phase modulation spectroscopy (PMS)
Light modulated into a sinusoidal wave of about 100 MHz is incident on the living body, and each hemoglobin concentration and oxygen saturation is calculated from the phase change and amplitude change of the light detected on the living body surface.

  Patent Document 1 describes a near-infrared noninvasive living body measuring apparatus. The apparatus described in this document has the following configuration in order to measure the oxygen state in a deep part of a living body with high accuracy using near infrared rays. That is, this apparatus includes a light emitting element that irradiates while changing the intensity of near-infrared light having two wavelengths, and a light receiving element that is disposed at a certain distance from the light emitting element and receives transmitted light from the light. And a control unit that calculates the absorbance of each of the two wavelengths at the intensity and applies the absorbance to the Beer-Lambert rule to calculate the oxygen state of the living body.

  Non-Patent Document 1 describes a method for non-invasively measuring the optical characteristics of a tissue using a time-resolving method.

Utility Model Registration No. 3016160

Michael S. Patterson, B. Chance, and B. C. Wilson, “Time resolvedreflectance and transmittance for the noninvasive measurement of tissue opticalproperties”, APPLIED OPTICS, Vol. 28, No. 12 (1989)

  Of the three measurement methods described above, time-resolved spectroscopy requires a light source that generates pulsed light of several picoseconds and a detector that can time-resolve detection signals with a time width of several picoseconds. This increases the cost of the device. Furthermore, since the calculation based on the light diffusion theory is performed, a burden on the arithmetic processing device is increased. In addition, phase modulation spectroscopy requires a highly accurate phase detection technique in order to detect a change in the phase of the detection light, which increases the cost of the apparatus. Furthermore, the configuration of the apparatus becomes complicated in order to detect the phase change and amplitude change of the detection light. To solve these problems, spatially resolved spectroscopy uses continuous light (CW light) and does not require any special configuration for light detection, so it has a very simple configuration compared to the above two methods. Measurements can be taken.

  However, there are also problems with spatially resolved spectroscopy. In spatially-resolved spectroscopy, since multiple light detection positions are provided, the contact state between the light detector and the living body surface and the light propagation path differ for each light detection position, and these differences appear as measurement errors. . In addition, the measurement accuracy decreases due to variations in the detection characteristics of the photodetector at each light detection position.

  In the apparatus described in Patent Document 1, only one light incident position and one light detection position are used, and the above-described problem is avoided. However, with the measuring method employed by this apparatus, it is difficult in principle to calculate the oxygen saturation with high accuracy (see Non-Patent Document 1, especially Equation 16. Even if the light amount is changed, the optical path length, That is, the depth information obtained does not change).

  The present invention has been made in view of such problems, and has only one light incident position and one light detection position, and an oxygen saturation measuring apparatus and oxygen capable of accurately calculating oxygen saturation. An object of the present invention is to provide a saturation calculation method.

  In order to solve the above-described problem, an oxygen saturation measuring apparatus according to the present invention is an apparatus for measuring oxygen saturation in a living body, and includes first and second wavelengths different from each other from one light incident position to a living body. From the light incident part which injects 2nd light, the light detection part which detects the light intensity of the 1st and 2nd light which propagated the inside of the biological body in one light detection position, and the detection result in a light detection part A calculation unit that calculates the oxygen saturation level in the living body by applying the calculated attenuation of the first and second light in the living body to Modified Beer-Lambert rule, and the calculation unit includes the first and second in vivo The optical path lengths of the second light are substantially equal to each other, and the sum of the absorption term and the scattering term by the light-absorbing substance other than hemoglobin with respect to the first light, and the absorption term and scattering by the light-absorbing substance other than the hemoglobin with respect to the second light The ratio of the sum to the term is Assuming approximately equal to the ratio between the luminous intensity and the attenuation of the second light, and calculates the oxygen saturation.

  Further, the oxygen saturation calculation method according to the present invention is a method for calculating oxygen saturation in an apparatus for measuring oxygen saturation in a living body, and has a wavelength different from each other in a living body from one light incident position. Decrease in the first and second light in the living body obtained by detecting the light intensities of the first and second light incident on the first and second light and propagating in the living body at one light detection position. A calculation step of calculating in-vivo oxygen saturation by applying the luminous intensity to the Modified Beer-Lambert rule, wherein in the calculation step, the optical path lengths of the first and second light in the living body are substantially equal to each other; The ratio of the sum of the absorption term and the scattering term of the light-absorbing substance other than hemoglobin relating to the first light and the sum of the absorption term and the scattering term of the light-absorbing substance other than the hemoglobin relating to the second light is reduced by the first light. Decrease in luminous intensity and second light Assuming equal to the ratio of the degree, and calculates the oxygen saturation.

Further, in the oxygen saturation measuring apparatus and the oxygen saturation calculating method described above, the calculation unit (or calculation step) calculates the oxygen saturation of a certain living body calculated based on the assumption and the oxygen saturation of the living body in advance. The following correction formula (1) based on the comparison with the measured results

(However, SO ₂ is the oxygen saturation calculated based on the assumption, SO _{2 and corr} are the corrected oxygen saturation, and a and b are real numbers), and the oxygen saturation calculated for other living bodies is corrected. It may be characterized by.

In addition, the oxygen saturation measuring device and the oxygen saturation calculating method include a calculation unit (or calculation step) in which the following calculation formula (2)

(However, SO ₂ is the oxygen saturation calculated based on the assumption, λ ₁ is the wavelength of the first light, λ ₂ is the wavelength of the second light, and ε _HbO2 (λ) is the oxyhemoglobin of the light of the wavelength λ. Calculate oxygen saturation using the molar extinction coefficient, ε _Hb (λ) is the molar extinction coefficient of deoxyhemoglobin for light of wavelength λ, and OD (λ, t) is the extinction of light of wavelength λ at time t). May be a feature.

  According to the oxygen saturation measuring apparatus and the oxygen saturation calculating method according to the present invention, it is possible to calculate the oxygen saturation with high accuracy by using only one light incident position and one light detection position.

It is a block diagram which shows the structure of the oxygen saturation measuring apparatus which concerns on one Embodiment of this invention. (A) It is a top view which shows the external appearance of the probe with which the oxygen saturation measuring apparatus of one Embodiment is provided. (B) It is sectional drawing along the II-II line | wire shown by (a). It is a figure which shows the state with which the probe was mounted | worn on the surface of the biological body. It is a figure which shows notionally the method of using a neutral density filter (ND filter) as an example of the calculation method of coefficient K ((lambda)). It is a figure which shows notionally the method of monitoring the intensity | strength of light in a light-incidence part as another example of the calculation method of coefficient K ((lambda)). It is a flowchart which shows the oxygen saturation calculation method which concerns on one Embodiment of this invention. As an example, it is a graph which shows the result of having measured the oxygen saturation in the right forehead part by a breath-taking experiment. As an example, it is a graph which shows the result of having measured the oxygen saturation in the right forehead part by a breath-taking experiment.

  Embodiments of an oxygen saturation measuring device and an oxygen saturation calculating method according to the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a block diagram showing a configuration of an oxygen saturation measuring apparatus according to an embodiment of the present invention. FIG. 2A is a plan view showing the appearance of the probe 20 provided in the oxygen saturation measuring apparatus of the present embodiment, and FIG. 2B is a cross-sectional view taken along the line II-II shown in FIG. It is sectional drawing along a line. FIG. 3 is a diagram showing a state in which the probe 20 is mounted on the surface of the living body A.

As shown in FIG. 1, the oxygen saturation measuring apparatus 1 </ b> A of this embodiment includes a main body 10 and a probe 20. The oxygen saturation measuring apparatus 1A includes a first light (wavelength λ ₁ ) and a second light (wavelength λ ₂ ≠ λ) from a probe 20 fixed to a part of a living body (for example, the head) at one light incident position. ₁ ) is a device that calculates hemoglobin oxygen saturation by detecting the intensity of light emitted from one light detection position in a living body. For example, near infrared light is used as the first and second light.

  As shown in FIG. 2, the probe 20 has a light incident part 21 and a light detection part 22. The light incident part 21 and the light detection part 22 are arranged with an interval of, for example, about several centimeters, and are substantially integrated by a flexible black rubber holder 23. The probe 20 can be fixed to the forehead portion having no hair, for example, with an adhesive tape, an elastic band, or the like.

  As shown in FIG. 3, the light incident portion 21 enters the first and second lights L <b> 1 and L <b> 2 from one light incident position P <b> 1 toward the living body A. The light incident portion 21 includes a semiconductor light emitting element such as a light emitting diode (LED). The light incident portion 21 makes the first and second lights L1 and L2 emitted from the semiconductor light emitting element incident substantially perpendicular to the surface of the living body A. Note that power for driving the semiconductor light emitting element is sent from the main body 10 via the cable 28.

  The light detection unit 22 detects the light intensities of the first and second lights L1 and L2 propagated inside the living body at one light detection position P2, and generates an electrical detection signal corresponding to the light intensity. To do. The light detection unit 22 includes a semiconductor light receiving element such as a Si PIN photodiode. Note that the light detection unit 22 may further include a preamplifier unit that integrates and amplifies the photocurrent output from the semiconductor light receiving element. Thereby, a weak signal can be detected with high sensitivity to generate a detection signal, and this signal can be transmitted to the main body 10 via the cable 28.

  Referring to FIG. 1, the main body unit 10 includes a drive unit (driver) 11, a sample hold circuit 12, an A / D conversion circuit 13, a CPU 14, a display unit 15, a ROM 16, a RAM 17, and a data bus 18.

The drive unit 11 is configured by a circuit that drives the semiconductor light emitting element of the light incident unit 21. The drive unit 11 is electrically connected to the data bus 18 and receives an instruction signal for instructing driving of the semiconductor light emitting element from the CPU 14 also electrically connected to the data bus 18. The instruction signal includes information such as the light intensity and wavelength (for example, one of the wavelengths λ ₁ and λ ₂ ) of the light output from the semiconductor light emitting element. The drive unit 11 drives the semiconductor light emitting element based on the instruction signal received from the CPU 14 and makes light enter the living body. The configuration of the light incident portion is not limited to that of the present embodiment, and the first and second lights are sent from the light emitting element accommodated in the main body portion 10 to the light incident portion of the probe 20 via the optical fiber. It may be configured.

  The sample hold circuit 12 and the A / D conversion circuit 13 receive the detection signal transmitted from the probe 20 via the cable 28, hold (hold) it, convert it into a digital signal, and output it to the CPU 14. The sample hold circuit 12 is electrically connected to the A / D conversion circuit 13 and outputs the held detection signal to the A / D conversion circuit 13.

  The A / D conversion circuit 13 is means for converting the detection signal from an analog signal to a digital signal. The A / D conversion circuit 13 converts the detection signal received from the sample hold circuit 12 into a digital signal. The A / D conversion circuit 13 is electrically connected to the data bus 18 and outputs the converted detection signal to the CPU 14 via the data bus 18.

  The CPU 14 is a calculation unit in the present embodiment, and calculates the oxygen saturation of hemoglobin contained in the living body based on the detection signal received from the A / D conversion circuit 13. A calculation program for this purpose is stored in the ROM 16. The CPU 14 sends time-series data indicating the calculated hemoglobin oxygen saturation to the display unit 15 via the data bus 18. The display unit 15 is electrically connected to the data bus 18 and displays the result sent from the CPU 14 via the data bus 18.

  Here, a method for calculating the hemoglobin oxygen saturation based on the detection signal will be described. In the present embodiment, the CPU 14 applies the dimming degree of the first and second lights L1 and L2 in the living body obtained from the detection result in the light detection unit 22 to the modified Beer-Lambert rule, so Calculate oxygen saturation.

Now, when near-infrared light of wavelength λ is irradiated into the living body from the light incident part 21, the light attenuation OD (λ, t) of light of wavelength λ at a certain time t applies the Modified Beer-Lambert rule. It is expressed as the following equation (3).

However, in Equation (3), the definition of each variable is as follows.
I _in (λ): incident light intensity of light of wavelength λ I _out (λ, t): detected light intensity of light of wavelength λ ε _HbO2 (λ): molar absorption coefficient ε _Hb of light of wavelength λ λ): molar absorption coefficient of deoxyhemoglobin with respect to light of wavelength λ [HbO ₂ ] (t): in vivo oxyhemoglobin concentration [Hb] (t): in vivo deoxyhemoglobin concentration [tHb] (t): in vivo Total hemoglobin concentration SO ₂ (t): oxygen saturation L (λ, t) in the living body: optical path length of light of wavelength λ A (λ, t): light-absorbing substance other than hemoglobin (for example, cytochrome c oxidase, myoglobin , Water, fat, etc.) absorption term S (λ, t): scattering term Oxygen saturation SO ₂ (t) is a value defined by the following equation.

When the above equation (3) is applied to near-infrared light of λ = λ ₁ and λ ₂ , the following equations (5) and (6) are obtained. In one embodiment, λ ₁ is 735 nm and λ ₂ is 850 nm.

Here, in the present embodiment, the CPU 14 calculates the oxygen saturation based on the following assumption (approximation). First, it is assumed (approximate) that the optical path lengths of the first and second lights L1 and L2 in the living body are equal to each other. This assumption is expressed by the following formula (7).

Next, the ratio of the sum of the absorption term and the scattering term due to the light-absorbing substance other than hemoglobin relating to the first light L1 and the sum of the absorption term and the scattering term due to the light-absorbing substance other than the hemoglobin relating to the second light L2 is as follows: Assume that it is equal to the ratio of the dimming degree of the first light L1 and the dimming degree of the second light L2. This assumption (approximation) is expressed by the following mathematical formula (8).

By introducing the above assumption (approximation), the oxygen saturation SO ₂ (t) is calculated using the following equation (9) from the equations (5) and (6) described above.

In the above equation (9), the molar extinction coefficient epsilon _HbO2 a (lambda) and epsilon _Hb (lambda), for example, _{ε HbO2 (λ 1) = 0.4646} , ε Hb (λ 1) = 1.2959, ε _{HbO2 (λ 2) = 1.1596,} ε Hb (λ 2) = 0.7861 ( units respectively ^mM -1 ^{cm -1)} can be.

In the formula (9), OD (λ, t) is obtained by the following formula (10).

Here, ADC (λ, t) is the detected light intensity of the light of wavelength λ, ADC _DARK (t) is a voltage-converted 12-bit A / D count value corresponding to the magnitude of the dark current, and K (Λ) is a conversion coefficient for converting a value corresponding to the magnitude of the pulse driving forward current I _Fin (λ) of the semiconductor light emitting element into a 12-bit A / D count value. If the gain of the light detection unit 22 (for example, the gain of the first-stage transimpedance amplifier is 1.0 × 10 ⁷ times and the gain of the next-stage programmable gain amplifier is 20 times) is unified to a constant value for a plurality of living bodies, the conversion The coefficient K (λ) can be applied to the same value for a plurality of living bodies. At that time, the detected light intensity ADC (λ, t) and the dark current equivalent value ADC _DARK (t) show various values depending on the optical constants (absorption coefficient, equivalent scattering coefficient) of a plurality of living bodies. .

In the present embodiment, the corrected oxygen saturation SO _{2, corr} (t) may be calculated using the following equation (11) obtained by correcting the equation (9). However, a and b are real numbers.

A in this formula (11), b is the equation (7) and (8) and calculated certain biological oxygen saturation _SO 2 (t) based on the assumption of, in advance the biometric oxygen saturation _SO 2 ( t) is a value obtained based on a comparison with the result of measurement by other means.

An example of a method for calculating the coefficient K (λ) of the above formula (10) will be described. FIG. 4 is a diagram conceptually illustrating a method using a neutral density filter (ND filter) as an example of a method for calculating the coefficient K (λ). In this method, the light incident part 21 and the light detection part 22 are disposed so as to face each other, and an ND filter 24 having a known transmittance is disposed therebetween. The light emitted from the light incident part 21 passes through the ND filter 24 and is attenuated, and reaches the light detection part 22. In addition, in FIG. 4, the structure which has three LED21a-21c as an example of the light-incidence part 21 is shown. LED21a and 21b emits light first light L1 having a wavelength lambda _1, and the wavelength lambda ₂ of the second light L2, respectively. The LED 21c emits third light L3 having a wavelength λ ₃ (for example, 810 nm) different from the wavelengths λ ₁ and λ ₂ . The light detection unit 22 includes a semiconductor light receiving element such as a Si PIN photodiode, for example, and a transimpedance amplifier (TIA) 22b and a programmable gain amplifier (PGA) 22c provided in the subsequent stage.

In the configuration shown in FIG. 4, light L <b> _{1 to} L <b> _{3 having} wavelengths λ _{1 to} λ ₃ are sequentially output from the light incident unit 21, and the light intensity after passing through the ND filter 24 is detected by the light detection unit 22. At this time, the A / D count value (for example, 12 bits) of the detection light may be acquired while gradually increasing the forward current amount of the LEDs 21a to 21c to gradually increase the light intensity of each of the lights L1 to L3. As a result, the values corresponding to the magnitudes of the pulse drive forward currents I _Fin (λ ₁ ), I _Fin (λ ₂ ), and I _Fin (λ ₃ ) given to the LEDs 21a to 21c are converted into 12-bit A / D count values. A calibration curve for conversion is obtained. Then, by dividing the 12-bit A / D count value by the spectral transmittance of the ND filter 24, the 12-bit A / D count equivalent value of the light intensities of the lights L1 to L3 (the forward current amounts of the LEDs 21a to 21c) is obtained. Thus, conversion coefficients K (λ ₁ ), K (λ ₂ ), and K (λ ₃ ) are obtained. Since these conversion factors depend only on the apparatus, they are preferably measured in advance and read from the ROM 16 (parameter database unit) shown in FIG.

FIG. 5 is a diagram conceptually illustrating a method of monitoring the intensity of the light L1 to L3 in the light incident unit 21, as another example of the method for calculating the coefficient K (λ). In this method, monitoring units (for example, monitoring photodiodes) 25 a to 25 c are arranged in the vicinity of the LEDs 21 a to 21 c inside the light incident portion 21. These monitor units 25a to 25c detect the light intensities of the lights L1 to L3 emitted by the LEDs 21a to 21c, respectively, and convert them into photocurrents. These photocurrents are converted into 12-bit A / D count values by the TIAs 26a to 26c, the PGAs 27a to 27c, and the ADCs 28a to 28c provided in the light incident part 21 or the main body part 10, respectively. Thereby, conversion factors K (λ ₁ ), K (λ ₂ ), and K (λ ₃ ) are obtained.

  FIG. 6 is a flowchart showing the oxygen saturation calculation method according to this embodiment. In this oxygen saturation calculation method, first, first and second lights L1 and L2 having different wavelengths are incident on the living body A from one light incident position P1 (light incident step S11). Next, the light intensity of the 1st and 2nd light L1, L2 which propagated the inside of the biological body A is detected in one light detection position P2 (light detection step S12).

Subsequently, the light intensity OD (λ, t) of the first and second lights L1 and L2 in the living body A obtained from the detection result in the light detection step S12 is applied to the Modified Beer-Lambert rule, and the living body A The oxygen saturation level SO ₂ (t) is calculated (calculation step S13). In the calculation step S13, it is preferable to calculate the oxygen saturation SO ₂ (t) using the above-described mathematical formula (9). Furthermore, in the calculation step S13, it is more preferable to correct the oxygen saturation using the correction equation (11) described above.

  The effects obtained by the oxygen saturation measuring apparatus 1A and the oxygen saturation calculating method of the present embodiment having the above-described configuration will be described. In the oxygen saturation measuring apparatus 1A and the oxygen saturation calculating method, only one light incident position P1 and one light detection position P2 are provided. Therefore, compared to an apparatus that employs spatially resolved spectroscopy (SRS method) that provides a plurality of light detection positions, the contact state between the light detection unit 22 and the surface of the living body A can be suppressed from appearing in the measurement error, Since it is possible to avoid the influence of variation in the detection characteristics of the light detection unit 22 at the light detection position P2, more accurate measurement can be performed. Therefore, according to the oxygen saturation measuring apparatus 1A and the oxygen saturation calculating method of the present embodiment, the oxygen saturation can be calculated with high accuracy.

  Further, according to the oxygen saturation measuring apparatus 1A of the present embodiment, the number of photodetectors can be reduced compared to an apparatus having a plurality of light detection positions, contributing to simplification and cost reduction of the apparatus. can do. Furthermore, compared with the apparatus described in Patent Document 1, it is not necessary to change the incident light intensity during measurement, so that the apparatus can be simplified and highly reproducible.

Further, as in the present embodiment, it is preferable to correct the oxygen saturation using the correction formula (11). Here, FIG.7 and FIG.8 is a graph which shows the result of having measured the oxygen saturation in the right forehead part by a breath-taking experiment as one Example of this embodiment. 7 and 8, the horizontal axis represents elapsed time (unit: seconds), the vertical axis (right) represents light attenuation (arbitrary unit), and the vertical axis (left) represents oxygen saturation (unit). :%). Moreover, in FIG.7 and FIG.8, the following graphs G11-G16 are shown.
Graph G11: Light attenuation graph at a wavelength of 735 nm G12: Light attenuation graph at a wavelength of 810 nm G13: Light attenuation graph at a wavelength of 850 nm G14: Corrected arteriovenous mixed blood oxygen saturation graph G15 calculated by Equation (11) : Percutaneous arterial oxygen saturation graph G16 measured with a commercially available pulse oximeter: Arteriovenous blood oxygen saturation in the left forehead using another TRS device (MBL method)

As shown in FIG. 16, in the corrected arteriovenous mixed blood oxygen saturation (graph G14), it starts from 75%, increases once to 80% after the start of breathing (time 0 second), and then increases to 70%. There was a change that seems to be appropriate, such as a decrease and recovery to 85% after resumption of breathing (time 75 seconds). Moreover, it was shown that such a change was in good agreement with the oxygen saturation (graph G15) measured by a commercially available pulse oximeter. Further, as shown in FIG. 17, the corrected oxygen saturation (graph G14) shows better breathing and resumption of breathing than the corrected oxygen saturation (graph G16). I understood it. In the present embodiment, the value a in Equation (11) is 10 and the value b is 3.48. The conversion factors were K (735) = 1.3 × 10 ⁹ and K (850) = 8.0 × 10 ⁸ .

  The oxygen saturation measuring device and the oxygen saturation calculating method according to the present invention are not limited to the above-described embodiments, and various other modifications are possible. For example, in the above-described embodiment, the correction formula according to Formula (11) is used, and this formula is a primary formula of y = ax−b. However, the correction formula is a formula other than the primary formula (for example, a secondary formula). Etc.).

DESCRIPTION OF SYMBOLS 1A ... Oxygen saturation measuring apparatus, 10 ... Main body part, 11 ... Drive part, 12 ... Sample hold circuit, 13 ... Conversion circuit, 14 ... CPU, 15 ... Display part, 16 ... ROM, 17 ... RAM, 18 ... Data bus , 20 ... probe, 21 ... light incident part, 22 ... light detection part, 23 ... holder, 24 ... ND filter, 28 ... cable, A ... biological body, P1 ... light incidence position, P2 ... light detection position.

Claims (6)

An apparatus for measuring oxygen saturation in a living body,
A light incident part for entering the first and second light having different wavelengths into the living body from one light incident position;
A light detection unit for detecting the light intensity of the first and second light propagated in the living body at one light detection position;
A calculation unit that calculates the oxygen saturation in the living body by applying the attenuation of the first and second light in the living body obtained from the detection result in the light detecting unit to Modified Beer-Lambert rule. Prepared,
The arithmetic unit has optical path lengths of the first and second lights in the living body substantially equal to each other, and a sum of an absorption term and a scattering term by a light-absorbing substance other than hemoglobin related to the first light, Assume that the ratio of the absorption term and the sum of the scattering terms by the light-absorbing substance other than hemoglobin with respect to the second light is approximately equal to the ratio of the attenuation of the first light to the attenuation of the second light. And calculating the oxygen saturation. The calculation unit is based on a comparison between the oxygen saturation of the living body calculated based on the assumption and the result of measuring the oxygen saturation of the living body in advance.

(Where SO ₂ is the oxygen saturation calculated based on the above assumption, SO _{2 and corr} are the corrected oxygen saturation, and a and b are real numbers), and the oxygen saturation calculated for the other living body. The oxygen saturation measuring apparatus according to claim 1, wherein: The calculation unit has the following calculation formula:

(Where SO ₂ is the oxygen saturation calculated based on the above assumption, λ ₁ is the wavelength of the first light, λ ₂ is the wavelength of the second light, and ε _HbO2 (λ) is the light of wavelength λ. Oxyhemoglobin molar extinction coefficient, ε _Hb (λ) is the deoxyhemoglobin molar extinction coefficient for light of wavelength λ, and OD (λ, t) is the degree of attenuation for light of wavelength λ at time t). The oxygen saturation measuring apparatus according to claim 1, wherein the oxygen saturation measuring apparatus calculates the oxygen saturation. A method of calculating oxygen saturation inside an apparatus for measuring oxygen saturation in a living body,
The first and second lights having different wavelengths are incident on the living body from one light incident position, and the light intensities of the first and second lights propagated in the living body are measured at one light detection position. A calculation step of calculating oxygen saturation in the living body by applying the attenuation of the first and second light in the living body obtained by detection to the Modified Beer-Lambert rule,
In the calculating step, the optical path lengths of the first and second light in the living body are substantially equal to each other, and the sum of the absorption term and the scattering term by the light-absorbing substance other than hemoglobin related to the first light, Assume that the ratio of the absorption term and the sum of the scattering terms by the light-absorbing substance other than hemoglobin with respect to the second light is approximately equal to the ratio of the attenuation of the first light to the attenuation of the second light. And calculating the oxygen saturation. In the calculation step, the following correction equation was formulated based on a comparison between the oxygen saturation of the living body calculated based on the assumption and the result of measuring the oxygen saturation of the living body in advance.

(Where SO ₂ is the oxygen saturation calculated based on the above assumption, SO _{2 and corr} are the corrected oxygen saturation, and a and b are real numbers), and the oxygen saturation calculated for the other living body. The oxygen saturation calculation method according to claim 1, wherein: In the calculation step, the following calculation formula

(Where SO ₂ is the oxygen saturation calculated based on the above assumption, λ ₁ is the wavelength of the first light, λ ₂ is the wavelength of the second light, and ε _HbO2 (λ) is the light of wavelength λ. Oxyhemoglobin molar extinction coefficient, ε _Hb (λ) is the deoxyhemoglobin molar extinction coefficient for light of wavelength λ, and OD (λ, t) is the degree of attenuation for light of wavelength λ at time t). The oxygen saturation calculation method according to claim 1 or 2, wherein calculation is performed.