JP6703841B2 - Pulse photometer and method for calculating blood light-absorbing substance concentration - Google Patents

Description

The present invention relates to a pulse photometer for calculating a blood light-absorbing substance concentration of a subject, and a method for calculating the blood light-absorbing substance concentration using the pulse photometer.

The pulse photometer is a device that calculates the concentration of the light-absorbing substance in the blood of the subject. Specifically, light of a plurality of wavelengths having different ratios of blood absorption coefficients depending on the concentration of the light absorbing substance in the blood is applied to the living tissue of the subject. The amount of light of each wavelength transmitted or reflected by the living tissue is detected. The amount of light of each wavelength changes with the pulsation of blood of the subject. Therefore, a temporal change in the amount of light of each wavelength due to pulsation is acquired as a pulse wave signal. The amplitude of the pulse wave signal associated with each wavelength corresponds to the amount of change in extinction degree associated with that wavelength. The concentration of the light-absorbing substance in blood is calculated based on the ratio of the amount of change in extinction degree for each wavelength (see, for example, Patent Document 1).

As an example of the blood light-absorbing substance concentration, arterial oxygen saturation (hereinafter referred to as SaO2) used as an index of blood oxygenation is known. Since invasive measurement is required to obtain the value of SaO2, percutaneous arterial oxygen saturation (hereinafter referred to as SpO2), which allows non-invasive calculation, is widely used as the index. ing. SpO2 is measured by a pulse oximeter, which is an example of a pulse photometer.

Japanese Patent No. 4196209

Ideally, the calculated SpO2 value is equal to the actual SaO2 value. However, it is known that the two values may deviate under certain conditions. In particular, when the amplitude of the pulse wave signal is small, the value of SpO2 tends to be calculated higher than the actual value of SaO2. In this case, even if the value of SpO2 indicates the normal state of the subject, a situation may occur in which the subject actually falls into hypoxemia.

Therefore, an object of the present invention is to improve the accuracy of the blood light-absorbing substance concentration calculated non-invasively.

In order to achieve the above object, the first aspect of the present invention is a pulse photometer,
A first light emitting unit configured to emit a first light including a first wavelength,
A second light emitting portion configured to emit a second light including a second wavelength,
The first intensity signal is output according to the intensity of the first light transmitted or reflected through the body of the subject, and the second intensity signal is output according to the intensity of the second light transmitted or reflected through the body. A light receiving unit configured to output,
Based on the first intensity signal, a first change amount acquisition unit configured to acquire a first change amount corresponding to the change amount of extinction degree of the first light due to pulsation of blood of the subject. When,
Based on the second intensity signal, a second change amount acquisition unit configured to obtain a second change amount corresponding to the dimming degree change amount of the second light due to the pulsation,
Based on the first amount of change and the second amount of change, a concentration calculation unit configured to calculate the blood light-absorbing substance concentration in the blood,
Is equipped with
The second change amount includes a first correction amount based on an inverse value of the first light extinction change amount.

The value of the blood light-absorbing substance concentration obtained by the pulse photometer tends to have a large error, particularly when the amplitude of the pulse wave signal is small. The inventors paid attention to the amount of change in the extinction degree of the first light corresponding to the amplitude of the pulse wave signal, and investigated the relationship with the error. As a result, the inventors have found that the reciprocal value of the first light extinction change amount and the magnitude of the error are in a proportional relationship. The magnitude of the error is represented as the difference between the measured value Cm of the blood light-absorbing substance concentration and the reference value Cr. Here, k1 is a proportional constant.

Cm-Cr=-k1/ΔA1

From this, the following equation is obtained.

Cr=Cm+(k1/ΔA1)

That is, it is understood that the reference value Cr can be obtained by adding the correction value to the measurement value Cm measured by the pulse photometer.

On the other hand, the concentration of the light-absorbing substance in blood is a function of the extinction change ratio Φ21 (=ΔA2/ΔA1), which is the ratio of the extinction change amount ΔA1 of the first light and the extinction change amount ΔA2 of the second light. .. Therefore, the following equation is obtained.

Cr ∝ Φ21+(k1/ΔA1)
∝(ΔA2/ΔA1)+(k1/ΔA1)
∝(ΔA2+k1)/ΔA1

That is, it can be seen that the measurement value Cm measured by the pulse photometer can be brought close to the reference value Cr by adding the correction amount corresponding to the proportional constant k1 obtained from the above-mentioned relation to the change amount ΔA2 of the second light extinction degree. ..

The second change amount acquisition unit is configured to acquire the second change amount corresponding to the second light extinction degree change amount ΔA2. The second variation amount is set to (ΔA2+k1) based on the above knowledge.

With such a configuration, it is possible to improve the accuracy of the blood light-absorbing substance concentration calculated non-invasively.

The above pulse photometer can be configured as follows.
The first correction amount is a constant that is statistically determined in advance based on a plurality of blood light-absorbing substance concentrations obtained from a plurality of subjects.

According to such a configuration, the second change amount acquisition unit operates based on the first correction amount which is a statistically determined constant. This not only improves the reliability of the first correction amount, but also suppresses the processing load on the second change amount acquisition unit. Therefore, it is possible to easily improve the accuracy of the blood light-absorbing substance concentration calculated non-invasively.

The above pulse photometer can be configured as follows.
One of the first light and the second light is red light,
The other of the first light and the second light is infrared light.

Red light and infrared light are a combination in which the ratio of the extinction coefficient of blood differs depending on the oxygen saturation. Therefore, according to such a configuration, especially SpO2 can be accurately calculated.

The above pulse photometer can be configured as follows.
A third light emitting part,
A third change amount acquisition unit,
Is equipped with
The third light emitting unit is configured to emit a third light including a third wavelength,
The light receiving unit is configured to output a third intensity signal according to the intensity of the third light transmitted or reflected by the body,
The third change amount acquisition unit, based on the third intensity signal, is configured to acquire a third change amount corresponding to the extinction change amount of the third light due to the pulsation,
The concentration calculation unit is configured to calculate the blood light-absorbing substance concentration based on the first change amount, the second change amount, and the third change amount,
The third change amount includes a second correction amount based on the reciprocal value of the first light extinction change amount.

With such a configuration using three kinds of wavelengths, the accuracy of the blood light-absorbing substance concentration calculated non-invasively can be further improved.

In this case, the above pulse photometer can be configured as follows.
The second correction amount is a constant that is statistically determined in advance based on a plurality of blood light-absorbing substance concentrations obtained from a plurality of subjects.

According to such a configuration, the second change amount acquisition unit operates based on the first correction amount which is a statistically determined constant. Further, the third change amount acquisition unit operates based on the second correction amount that is a statistically determined constant. Thereby, not only the reliability of the first correction amount and the second correction amount is improved, but also the processing load on the second change amount acquisition unit and the third change amount acquisition unit can be suppressed. Therefore, it is possible to easily improve the accuracy of the blood light-absorbing substance concentration calculated non-invasively.

Further, the above pulse photometer can be configured as follows.
The first wavelength, the second wavelength, and the third wavelength are selected from 630 nm, 660 nm, 700 nm, 730 nm, 805 nm, 880 nm, and 940 nm.

According to such a configuration, not only SpO2 but also blood concentrations of carbon monoxide hemoglobin, Met hemoglobin, pigments injected into blood, and the like can be calculated.

Therefore, the second aspect of the present invention to achieve the above object is a pulse photometer,
Based on the first intensity signal corresponding to the intensity of the first light including the first wavelength transmitted or reflected by the body of the subject, the extinction degree of the first light accompanying the pulsation of blood of the subject. A first change amount acquisition unit configured to acquire a first change amount corresponding to the change amount,
Based on the second intensity signal corresponding to the intensity of the second light including the second wavelength transmitted or reflected by the body, the second change amount corresponding to the change amount of the dimming degree of the second light due to the pulsation. A second change amount acquisition unit configured to acquire
Based on the first amount of change and the second amount of change, a concentration calculation unit configured to calculate the blood light-absorbing substance concentration in the blood,
Is equipped with
The second change amount includes a first correction amount based on an inverse value of the first light extinction change amount.

Further, a third aspect that the present invention can take to achieve the above object is a method for calculating a blood light-absorbing substance concentration,
Based on the first intensity signal corresponding to the intensity of the first light including the first wavelength transmitted or reflected by the body of the subject, the extinction degree of the first light accompanying the pulsation of blood of the subject. The pulse photometer acquires the first change amount corresponding to the change amount,
Based on the second intensity signal corresponding to the intensity of the second light including the second wavelength transmitted or reflected by the body, the second change amount corresponding to the change amount of the dimming degree of the second light due to the pulsation. , Is acquired by the pulse photometer,
Based on the first change amount and the second change amount, the blood light-absorbing substance concentration in the blood, the pulse photometer to calculate,
The second change amount includes a first correction amount based on an inverse value of the first light extinction change amount.

It is a figure showing the functional composition of the pulse oximeter concerning a first embodiment. It is a figure for demonstrating operation|movement of the pulse oximeter of FIG. It is a figure showing functional composition of a pulse oximeter concerning a second embodiment. FIG. 4 is a diagram for explaining the operation of the pulse oximeter of FIG. 3.

Exemplary embodiments are described in detail below with reference to the accompanying drawings. FIG. 1 is a diagram showing a functional configuration of a pulse oximeter 1 (an example of a pulse photometer) according to the first embodiment. The pulse oximeter 1 is a device that measures SpO2 of the subject 2. SpO2 represents the ratio of oxyhemoglobin (an example of a blood light-absorbing substance) to the amount of hemoglobin capable of carrying oxygen (an example of a blood light-absorbing substance concentration).

The pulse oximeter 1 includes a first light emitting unit 11. The first light emitting unit 11 is configured to emit the first light including the first wavelength λ1. Examples of the first wavelength λ1 include 880 nm and 940 nm (an example of infrared light). The first light emitting unit 11 is, for example, a semiconductor light emitting element that can emit the first light. Examples of the semiconductor light emitting element include a light emitting diode (LED), a laser diode, an organic EL element and the like.

The pulse oximeter 1 includes a second light emitting unit 12. The second light emitting unit 12 is configured to emit the second light including the second wavelength λ2. Examples of the second wavelength λ2 include 630 nm and 660 nm (an example of red light). The second light emitting unit 12 is, for example, a semiconductor light emitting element capable of emitting the second light. Examples of the semiconductor light emitting element include a light emitting diode (LED), a laser diode, an organic EL element and the like.

The pulse oximeter 1 includes a light receiving unit 20. The light receiving unit 20 is configured to output the first intensity signal I1 according to the intensity of the first light transmitted or reflected by the body of the subject 2. Further, the light receiving unit 20 is configured to output the second intensity signal I2 according to the intensity of the second light transmitted or reflected by the body of the subject 2. The light receiving unit 20 is, for example, an optical sensor having sensitivity to the first wavelength λ1 and the second wavelength λ2. Examples of the optical sensor include a photodiode, a phototransistor, and a photoresistor.

The pulse oximeter 1 includes a first change amount acquisition unit 31. The first change amount acquisition unit 31 acquires the change amount ΔA1 of the first light extinction degree due to the pulsation of blood of the subject 2 based on the change over time of the first intensity signal I1 output from the light receiving unit 20. Is configured to. The first light extinction change amount ΔA1 is represented by the following equation.

ΔA1=ln [I1/(I1-ΔI1)]≈ΔI1/I1 (1)

Here, ΔI1 indicates the amount of change in the first intensity signal I1 due to the pulsation of blood of the subject 2.

The pulse oximeter 1 includes a second change amount acquisition unit 32. The second change amount acquisition unit 32 acquires the second light extinction change amount ΔA2 due to the pulsation of blood of the subject 2 based on the change over time of the second intensity signal I2 output from the light receiving unit 20. Is configured to. The change amount ΔA2 of the second light extinction degree is expressed by the following equation.

ΔA2=ln[I2/(I2-ΔI2)]≈ΔI2/I2 (2)

Here, ΔI2 indicates the amount of change in the second intensity signal I2 due to the pulsation of blood of the subject 2.

As described above, the value of SpO2 acquired by the pulse oximeter becomes higher than the value of arterial oxygen saturation (hereinafter referred to as SaO2) acquired invasively, especially when the amplitude of the pulse wave signal is small. Tend. The inventors paid attention to the first light extinction change amount ΔA1 corresponding to the amplitude of the pulse wave signal, and examined the relationship between the difference between the SpO2 value and the SaO2 value.

FIG. 2A shows the result. The horizontal axis corresponds to the reciprocal of the first light extinction change amount ΔA1. Therefore, the larger the value, the smaller the amplitude of the pulse wave signal. The vertical axis corresponds to the difference between the SpO2 value and the SaO2 value. That is, the vertical axis corresponds to the error amount included in the acquired SpO2 value. The inventors have found that the reciprocal value of the first light extinction change amount ΔA1 and the error amount included in the acquired SpO2 value are in a proportional relationship. That is, the following equation is obtained.

SpO2-SaO2=-k1/ΔA1 (3)

Here, k1 is a proportional constant.

The value of SaO2 can be regarded as the reference value of SpO2 acquired by the pulse oximeter. The reference value is represented by the following equation from the equation (3).

SaO2=SpO2+(k1/ΔA1) (4)

That is, the right side of Expression (3) can be regarded as a correction value necessary to obtain an accurate SpO2 value. According to the equation (4), it can be understood that the reference value can be obtained by adding the correction value to the SpO2 value acquired by the pulse oximeter.

On the other hand, SpO2 is a function of a dimming degree change amount ratio Φ21 (=ΔA2/ΔA1) which is a ratio between the dimming degree change amount ΔA1 of the first light and the dimming degree change amount ΔA2 of the second light. Therefore, the following equation is obtained from the equation (4).

SaO2∝Φ21+(k1/ΔA1)
∝(ΔA2/ΔA1)+(k1/ΔA1)
∝(ΔA2+k1)/ΔA1 (5)
That is, the value of SpO2 acquired by the pulse oximeter is calculated by adding the correction amount corresponding to the proportional constant k1 obtained from the relationship shown in FIG. 2A to the second light extinction change amount ΔA2. , SaO2 values can be approached.

The first change amount acquisition unit 31 is configured to acquire the first change amount Δ1 corresponding to the first light extinction degree change amount ΔA1. The first change amount Δ1 is substantially the same as the first light extinction change amount ΔA1.

The second change amount acquisition unit 32 is configured to acquire the second change amount Δ2 corresponding to the second light extinction degree change amount ΔA2. The second variation amount Δ2 is set according to the following equation based on the above findings.

Δ2=ΔA2+k1 (6)

k1 can be regarded as the first correction amount based on the reciprocal value of the first light extinction change amount ΔA1. That is, the second change amount Δ2 includes the first correction amount k1.

The pulse oximeter 1 includes a concentration calculator 40. The concentration calculation unit 40 calculates the SpO2 of the subject 2 based on the first change amount Δ1 acquired by the first change amount acquisition unit 31 and the second change amount Δ2 acquired by the second change amount acquisition unit 32. Is configured to calculate. Specifically, it is configured to calculate SpO2 based on the equation (5).

2B shows the difference between the value of SpO2 and the value of SaO2 calculated by the pulse oximeter 1 including the above-described concentration calculation unit 40, as in FIG. 2A. .. Although the difference between the two has not been resolved, as compared with an example in which the first correction amount k1 is not used, in a region where the pulse wave amplitude is small (a region where the reciprocal value of the first light extinction change amount ΔA1 is large). It can be seen that the error amount is reduced. Therefore, according to the above configuration, the accuracy of SpO2 calculated noninvasively can be improved.

The value of the first correction amount k1 can be set appropriately. In the present embodiment, the value of the first correction amount k1 is statistically determined in advance based on the difference value between the plurality of SpO2 and SaO2 obtained by the plurality of subjects. Specifically, the plurality of measurement results as shown in FIG. 2A are subjected to statistical processing such as the least squares method to determine the first correction amount k1 that can reduce the difference between SpO2 and SaO2. ..

With such a configuration, the second change amount acquisition unit 32 operates based on the first correction amount k1 which is a statistically determined constant. Thereby, not only the reliability of the first correction amount k1 is improved, but also the processing load on the second change amount acquisition unit 32 can be suppressed. Therefore, the accuracy of SpO2 calculated noninvasively can be easily improved.

In the present embodiment, infrared light is used as the first light and red light is used as the second light. However, red light may be used as the first light and infrared light may be used as the second light.

In the present embodiment, the common light receiving unit 20 is configured to receive the first light emitted from the first light emitting unit 11 and the second light emitted from the second light emitting unit 12. However, the light receiving portion for receiving the first light and the light receiving portion for receiving the second light may be separately provided.

FIG. 3 is a diagram showing a functional configuration of the pulse oximeter 1A according to the second embodiment. Constituent elements that are the same as or equivalent to those of the pulse oximeter 1 according to the first embodiment are given the same reference numerals, and repeated explanations are omitted.

The pulse oximeter 1A includes a third light emitting unit 13. The third light emitting unit 13 is configured to emit the third light including the third wavelength λ3. Examples of the third wavelength λ3 include 700 nm (an example of red light), 730 nm (an example of red light), 805 nm (an example of infrared light). The third light emitting unit 13 is, for example, a semiconductor light emitting element capable of emitting third light. Examples of the semiconductor light emitting element include a light emitting diode (LED), a laser diode, an organic EL element and the like.

The light receiving unit 20 is configured to output the third intensity signal I3 according to the intensity of the third light transmitted or reflected by the body of the subject 2.

The pulse oximeter 1A includes a third change amount acquisition unit 33. The third change amount acquisition unit 33 acquires the third light extinction change amount ΔA3 due to the pulsation of blood of the subject 2 based on the change over time of the third intensity signal I3 output from the light receiving unit 20. Is configured to. The third light extinction change amount ΔA3 is expressed by the following equation.

ΔA3=ln [I3/(I3−ΔI3)]≈ΔI3/I3 (7)

Here, ΔI3 indicates the amount of change in the third intensity signal I3 due to the pulsation of the blood of the subject 2.

FIG. 4A shows the relationship between the reciprocal value of the first light extinction change amount ΔA1 and the difference value between the SpO2 value and the SaO2 value when SpO2 is measured using three types of wavelengths. ing. The horizontal axis corresponds to the former and the vertical axis corresponds to the latter. The inventors have found that even when three types of wavelengths are used, the reciprocal value of the first light extinction change amount ΔA1 is proportional to the error amount included in the acquired SpO2 value.

SpO2 is also a function of the dimming degree change amount ratio Φ31 (=ΔA3/ΔA1), which is the ratio of the dimming degree change amount ΔA1 of the first light and the dimming degree change amount ΔA3 of the third light. Therefore, the following equation is obtained from the equation (4).

SaO2∝Φ21+(k1/ΔA1), Φ31+(k2/ΔA1)
∝(ΔA2/ΔA1)+(k1/ΔA1),
(ΔA3/ΔA1)+(k2/ΔA1)
∝(ΔA2+k1)/ΔA1, (ΔA3+k2)/ΔA1 (8)
That is, the first correction amount k1 obtained from the relationship shown in FIG. 4A is added to the second light extinction change amount ΔA2, and the second correction amount k2 is added to the third light extinction change amount ΔA3. It can be seen that the value of SpO2 obtained by the pulse oximeter can be brought close to the value of SaO2 by adding to the above.

The third change amount acquisition unit 33 is configured to acquire the third change amount Δ3 corresponding to the third light extinction degree change amount ΔA3. The third variation amount Δ3 is set according to the following equation based on the above findings.

Δ3=ΔA3+k2 (9)

k2 can be regarded as a second correction amount based on the reciprocal value of the first light extinction change amount ΔA1. That is, the third change amount Δ3 includes the second correction amount k2.

The pulse oximeter 1A includes a concentration acquisition unit 40A. The concentration acquisition unit 40 is acquired by the first change amount Δ1 acquired by the first change amount acquisition unit 31, the second change amount Δ2 acquired by the second change amount acquisition unit 32, and the third change amount acquisition unit 33. The SpO2 of the subject 2 is calculated based on the calculated third change amount Δ3. Specifically, it is configured to perform the following processing.

The first light extinction change amount ΔA1, the second light extinction change amount ΔA2, and the third light extinction change amount ΔA3 can be expressed by the following equations.

ΔA1=ΔAb1+ΔAt1=Eb1HbΔDb+Σt1ΔDt (10)
ΔA2=ΔAb2+ΔAt2=Eb2HbΔDb+Σt2ΔDt (11)
ΔA3=ΔAb3+ΔAt3=Eb3HbΔDb+Σt3ΔDt (12)

Here, E represents the extinction coefficient (dl g ^-1 cm ^-1 ). Hb represents the hemoglobin concentration in blood (g dl ^-1 ). Σ represents the extinction ratio (cm ⁻¹ ). ΔD represents a thickness change (cm) due to blood pulsation. The subscript b represents blood. The subscript t represents a tissue other than blood. The subscript 1 represents the first light. The subscript 2 represents the second light. The subscript 3 represents the third light.

Expressions (10) to (12) can be modified as follows.

ΔA1=Eb1HbΔDb+Σt1ΔDt
=[Eb1+(Σt1ΔDt)/(HbΔDb)](HbΔDb)
=(Eb1+Ex1)(HbΔDb) (13)
ΔA2=Eb2HbΔDb+Σt2ΔDt
=[Eb2+(Σt2ΔDt)/(HbΔDb)](HbΔDb)
=(Eb2+Ex2)(HbΔDb) (14)
ΔA3=Eb3HbΔDb+Σt3ΔDt
=[Eb3+(Σt3ΔDt)/(HbΔDb)](HbΔDb)
=(Eb3+Ex3)(HbΔDb) (15)

Here, Ex is a variable in which (ΣtΔDt)/(HbΔDb) is replaced. The subscript 1 represents the first light. The subscript 2 represents the second light. The subscript 3 represents the third light.

Expressions (13) to (15) can be modified as follows.

Eb1+Ex1-ΔA1/(HbΔDb)=0 (16)
Eb2+Ex2-ΔA2/(HbΔDb)=0 (17)
Eb3+Ex3-ΔA3/(HbΔDb)=0 (18)

Regarding Expressions (16) to (18), the extinction coefficient Eb2 of blood of the second light and the extinction coefficient Eb3 of blood of the third light are as follows by the extinction coefficient Eb1 of blood of the first light. Can be approximated.

Eb2=a2 Eb1+b2 (19)
Eb3=a3 Eb1+b3 (20)

Here, a and b are constants. The subscript 1 represents the first light. The subscript 2 represents the second light. The subscript 3 represents the third light.

Regarding Expressions (16) to (18), Ex2 of the second light and Ex3 of the third light can be approximated by Ex1 of the first light as follows.

Ex2=α2Ex1+β2 (21)
Ex3=α3Ex1+β3 (22)

Here, α and β are constants. The subscript 1 represents the first light. The subscript 2 represents the second light. The subscript 3 represents the third light.

By rewriting equations (16) to (18) using equations (19) to (22), the following equation is obtained.

Eb1+Ex1-ΔA1/(HbΔDb)=0 (23)

(A2Eb1+b2)+(α2Ex1+β2)−ΔA2/(HbΔDb)=0
a2Eb1+α2Ex1-ΔA2/(HbΔDb)=−b2-β2 (24)

(A3Eb1+b3)+(α3Ex1+β3)−ΔA3/(HbΔDb)=0
a3Eb1+α3Ex1-ΔA3/(HbΔDb)=-b3-β3 (25)

Therefore, the absorption coefficient Eb1 of the first light blood is obtained by calculating the following determinant.

When SpO2, which is expressed as a percentage, is expressed as a decimal with S, the extinction coefficient Eb1 is expressed by the following equation.

Eb1=Eo1S+Er1(1-S) (27)

Here, Eo represents the extinction coefficient of oxyhemoglobin. Er represents the extinction coefficient of deoxygenated hemoglobin. The subscript 1 represents the first light.

Here, the first correction amount k1 is added to the dimming degree change amount ΔA2 of the second light, and the second correction amount k2 is added to the dimming degree change amount ΔA3 of the third light to obtain the pulse oximeter. It can be seen that the value of SpO2 can approach the value of SaO2.

By rewriting the equation (28) using the equations (6) and (9), the following equation is obtained.

Therefore, the first change amount Δ1 acquired by the first change amount acquisition unit 31, the second change amount Δ2 acquired by the second change amount acquisition unit 32, and the third change amount acquired by the third change amount acquisition unit 33. It can be seen that the concentration calculation unit 40A is configured to calculate SpO2 based on the change amount Δ3.

4B shows the difference between the value of SpO2 and the value of SaO2 calculated by the pulse oximeter 1A including the above-described concentration calculation unit 40A, similarly to FIG. 4A. .. Compared with an example in which the first correction amount k1 and the second correction amount k2 are not used, the error amount is greatly reduced in the region where the pulse wave amplitude is small (the region where the reciprocal value of the first light extinction change amount ΔA1 is large). You can see that Therefore, according to the above configuration, the accuracy of SpO2 calculated noninvasively can be significantly improved.

The values of the first correction amount k1 and the second correction amount k2 can be set appropriately. In the present embodiment, the values of the first correction amount k1 and the second correction amount k2 are statistically determined in advance based on the difference values between the plurality of SpO2 and SaO2 obtained by the plurality of subjects. .. Specifically, the plurality of measurement results as shown in FIG. 4A are subjected to statistical processing such as the least squares method, and the first correction amount k1 and the second correction amount k1 that can reduce the difference between SpO2 and SaO2. The correction amount k2 is determined.

With such a configuration, the second change amount acquisition unit 32 operates based on the first correction amount k1 which is a statistically determined constant. In addition, the third change amount acquisition unit 33 operates based on the second correction amount k2 that is a statistically determined constant. Thereby, not only the reliability of the first correction amount k1 and the second correction amount k2 is improved, but also the processing load on the second change amount acquisition unit 32 and the third change amount acquisition unit 33 can be suppressed. Therefore, the accuracy of SpO2 calculated non-invasively can be easily and significantly improved.

In this embodiment, infrared light is used as the first light, and red light is used as the second light and the third light. However, red light may be used as the first light, red light may be used as one of the second light and third light, and infrared light may be used as the other. Alternatively, infrared light may be used for any two of the first light, second light, and third light, and red light may be used for the other one.

In the present embodiment, the common light receiving unit 20 emits the first light emitted from the first light emitting unit 11, the second light emitted from the second light emitting unit 12, and the third light emitting unit 13. It is configured to receive a third light. However, at least one of the light receiving portion for receiving the first light, the light receiving portion for receiving the second light, and the light receiving portion for receiving the third light may be provided independently.

Since the red light and the infrared light are a combination in which the ratio of the extinction coefficient of blood differs depending on the oxygen saturation, it is possible to improve the accuracy of the calculation of SpO2.

The above embodiments are merely examples for facilitating the understanding of the present invention. The configurations according to the above-described embodiments can be appropriately modified and improved without departing from the spirit of the present invention. Further, it is obvious that equivalents are included in the technical scope of the present invention.

In each of the above-mentioned embodiments, a pulse oximeter for calculating SpO2 is exemplified. However, the present invention is applicable to other pulse photometers that calculate the concentration of other light absorbing substances in blood. Other examples of the light absorbing substance in blood include carbon monoxide hemoglobin, Met hemoglobin, and a dye injected into blood. In that case, the wavelengths of the respective lights are selected so that the ratio of the extinction coefficient of blood is substantially different depending on the concentration of the target light-absorbing substance in blood.

It is possible to adopt a configuration in which four or more kinds of light including four or more kinds of wavelengths are used for specifying the blood light-absorbing substance concentration. For example, the four wavelengths λ1, λ2, λ3, and λ4 may be chosen as follows.
λ1=630 nm, λ2=660 nm, λ3=700 nm, λ4=880 nm
λ1=660 nm, λ2=700 nm, λ3=880 nm, λ4=940 nm

In each of the above-described embodiments, the functions of the first change amount acquisition unit 31, the second change amount acquisition unit 32, the third change amount acquisition unit 33, and the concentration calculation unit 40 (40A) are the processors connected to be communicable. It is realized by the software executed by the cooperation of the memory and the memory. Examples of the processor include CPU and MPU. Examples of the memory include RAM and ROM. However, at least one function of the first change amount acquisition unit 31, the second change amount acquisition unit 32, the third change amount acquisition unit 33, and the concentration calculation unit 40 (40A) is performed by hardware such as a circuit element, or It can be realized by a combination of hardware and software.

1, 1A: pulse oximeter, 2: subject, 11: first light emitting part, 12: second light emitting part, 13: third light emitting part, 20: light receiving part, 31: first change amount acquiring part, 32 : Second change amount acquisition unit, 33: third change amount acquisition unit, 40, 40A: concentration acquisition unit, λ1: first wavelength, λ2: second wavelength, λ3: third wavelength, I1: first intensity signal, I2: second intensity signal, I3: third intensity signal, ΔA1: first light extinction change amount, ΔA2: second light extinction change amount, ΔA3: third light extinction change amount, Δ1: first change amount, Δ2: second change amount, Δ3: third change amount, k1: first correction amount, k2: second correction amount

Claims (8)

A first light emitting unit configured to emit a first light including a first wavelength,
A second light emitting portion configured to emit a second light including a second wavelength,
The first intensity signal is output according to the intensity of the first light transmitted or reflected through the body of the subject, and the second intensity signal is output according to the intensity of the second light transmitted or reflected through the body. A light receiving unit configured to output,
Based on the first intensity signal, a first change amount acquisition unit configured to acquire the change amount of extinction degree of the first light due to the pulsation of blood of the subject,
Based on the second intensity signal, a second change amount acquisition unit configured to acquire the change amount of dimming degree of the second light due to the pulsation,
Configured concentrations to exert a first correction amount to the light absorbing material concentration in the blood in the first light attenuation variation and the second light attenuation variation of the blood which is calculated based on the ratio of A calculator,
Is equipped with
Wherein the first correction amount, the first and based on the inverse value of the attenuation amount of change in the optical correction the ratio of light attenuation variation of the attenuation variation of the first light and said second light To do
Pulse photometer. The first correction amount includes a proportional constant that is statistically determined in advance based on a plurality of blood light-absorbing substance concentrations obtained from a plurality of subjects,
The pulse photometer according to claim 1. One of the first light and the second light is red light,
The other of the first light and the second light is infrared light,
The pulse photometer according to claim 1. A third light emitting part,
A third change amount acquisition unit,
Is equipped with
The third light emitting unit is configured to emit a third light including a third wavelength,
The light receiving unit is configured to output a third intensity signal according to the intensity of the third light transmitted or reflected by the body,
The third change amount acquisition unit, based on the third intensity signal, is configured to acquire the extinction change amount of the third light due to the pulsation,
The concentration calculation unit, the first of the the attenuation amount of change in the optical second attenuation variation in ratio of light, and the first attenuation variation and the third attenuation of the light intensity of the light It is configured to add the first correction amount and the second correction amount to the blood light-absorbing substance concentration calculated based on the ratio of the change amount,
The second correction amount, the first and based on the inverse value of the attenuation amount of change in the optical correction the ratio of light attenuation variation of the attenuation variation of the first light and the third light To do
The pulse photometer according to any one of claims 1 to 3. The second correction amount includes a proportional constant that is statistically determined in advance based on a plurality of blood light-absorbing substance concentrations obtained from a plurality of subjects,
The pulse photometer according to claim 4. The first wavelength, the second wavelength, and the third wavelength are selected from 630 nm, 660 nm, 700 nm, 730 nm, 805 nm, 880 nm, and 940 nm,
The pulse photometer according to claim 4 or 5. Based on the first intensity signal corresponding to the intensity of the first light including the first wavelength transmitted or reflected by the body of the subject, the extinction degree of the first light accompanying the pulsation of blood of the subject. a first change amount acquiring unit configured to change the amount to acquire,
Based on the second intensity signal corresponding to the intensity of the second light including the second wavelength transmitted or reflected through the body, it is configured to obtain the amount of change in extinction of the second light due to the pulsation. Second change amount acquisition unit,
Configured concentrations to exert a first correction amount to the light absorbing material concentration in the blood in the first light attenuation variation and the second light attenuation variation of the blood which is calculated based on the ratio of A calculator,
Is equipped with
Wherein the first correction amount, the first and based on the inverse value of the attenuation amount of change in the optical correction the ratio of light attenuation variation of the attenuation variation of the first light and said second light To do
Pulse photometer. Based on the first intensity signal corresponding to the intensity of the first light including the first wavelength transmitted or reflected by the body of the subject, the extinction degree of the first light accompanying the pulsation of blood of the subject. Let the pulse photometer acquire the amount of change,
Based on a second intensity signal corresponding to the intensity of the second light including the second wavelength transmitted or reflected the body, the amount of change in extinction of the second light due to the pulsation, to the pulse photometer Let's get
Based on the ratio of the extinction change amount of the first light and the extinction change amount of the second light, the blood light-absorbing substance concentration in the blood is calculated by the pulse photometer,
Calculating said blood absorbing substance concentration was to, attenuation variation of light attenuation variation of the first and based on the inverse value of the attenuation amount of change in the optical said first light and said second light A first correction amount for correcting the ratio of the pulse photometer is added to the pulse photometer ,
Method for calculating the concentration of light-absorbing substances in blood.

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