JP3016160U - Near infrared non-invasive biometric device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a near-infrared non-invasive living body measuring apparatus capable of measuring the oxygen state in a deep part of a living body with high accuracy by using near-infrared rays. [Structure] Luminescent elements 1a and 1b for irradiating two wavelengths of near-infrared light with varying intensities and irradiating light, and light transmitted through the light-emitting elements 1a and 1b are arranged at a constant distance from the light emitting elements 1a and 1b. The actual absorbance is calculated from the light receiving elements 2a and 2b that receive light, the light emitting signals at the two wavelengths, and the light receiving signal obtained by subtracting the light receiving signals when the light intensity is strong and when the light intensity is weak. And a control unit 7 that adapts to the law and calculates the oxygen state of the living body.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a near-infrared non-invasive living body measuring device that non-invasively measures an oxygen state of a living body by using near-infrared rays.

[0002]

[Prior art]

 In general, the human body as a living body has cells in each part that survive due to oxygen in the blood, so during surgery on the heart, etc., the oxygen state of the cerebral cortex, especially the cerebral cortex, is measured in real time, and brain cells The state of is always checked. As a method of measuring the oxygen state of the cerebral cortex, a method of noninvasively measuring by using near-infrared ray having excellent tissue permeability is known.

In the biometric method using the near infrared rays, for example, a wavelength range from 600 nm to 1100 nm is used as the near infrared rays. This is because when the wavelength becomes short, the light is scattered by the living body, and when the wavelength becomes long, it is absorbed by water, and in any case, the light does not pass through. Therefore, the light emitting element of the light source irradiates the cerebral tissue of the skull with near-infrared rays, and this light is absorbed by oxygen hemoglobin and deoxyhemoglobin.Therefore, light that correlates with their concentration and the distance that light passes through is received by the light receiving element. To receive light. Therefore, the greater the distance from the light source and the greater the concentration, the more the light is absorbed and the less the light is received. Then, the concentration or amount of the hemoglobin to be measured is calculated from the relationship between the light emission signal and the light reception signal, and the Bear Lambert's law is used in this case.

Here, the absorption spectra of oxygen hemoglobin and reduced hemoglobin in blood in the near-infrared region have a characteristic that the absorbance at each wavelength is uniquely changed as shown in FIG. Light absorption in this region is a binary system mainly due to hemoglobin. Therefore, by measuring the absorbance at light of two specific wavelengths and using a spectroscopic method, the amount of oxygen and reduced hemoglobin, etc. can be determined. Can be measured. In addition, since the distance that light passes through in cerebral tissues cannot be directly measured, the oxygen saturation is calculated by the ratio of oxygen hemoglobin to the total concentration as the oxygen state.

Conventionally, as a method for actually measuring a living body by using the near infrared rays, there is one shown in FIG. Here, as shown in (a), when the intensity distribution of the light incident on the point A of the tissue in the tissue is shown, it becomes hemispherical as shown, and the intensity is inversely proportional to the exponential function of depth. Therefore, the transmitted light at the point B having the depth d becomes equal to the scattered light at the point C. Therefore, the Bear Lambert's law may be applied to the light receiving element 2 arranged at a distance d from the light source 1 on the surface of the tissue. In the case of the skull, the scalp is on the surface, the skull is below the skull, and the cerebral cortex is deep below the skull. For this reason, when light is emitted from the surface of the skull and the transmitted light is received, the received light signal also includes a signal that detects a shallow place such as the skull, so a signal corresponding to a deep place in the cerebral cortex is extracted from the received light signal. Therefore, it is necessary to measure the oxygen state of blood in the cerebral cortex with high accuracy.

Therefore, by utilizing the fact that the light reception signal reflects the situation of a deep place as the distance from the light source increases, different distances d 1 and d 2 from the light source 1 on the skull surface as shown in (b). Two light receiving elements 2a and 2b are arranged at two positions. Then, the light source 1 irradiates the skull with light having the same intensity but different wavelengths, and the light receiving element 2b having a long distance obtains a light receiving signal StD by the light n that passes through the whole at a deep position, that is, including the skull and the cerebral cortex. . Also, the light receiving signal StS by the light m passing through a shallow place, that is, mainly near the skull is obtained by the light receiving element 2a having a short distance. Then, the light receiving signal StS at the shallow place is regarded as common, and the light receiving signal StS at the shallow place is subtracted from the light receiving signal StD at the deep place to obtain the light receiving signal St passing only through the cerebral cortex, and based on this light receiving signal St It is designed to calculate oxygen saturation.

[0007]

[Problems to be solved by the device]

 By the way, in the above-mentioned prior art, although the light receiving signal StS of the light receiving element 2a having a short distance is regarded as common, the calculation is not completely common. That is, since there is only one light source, the light receiving signal StS of the light receiving element 2a having a short distance is common to the light receiving signal StD of the light receiving element 2b having a long distance in the vicinity thereof. However, since the two light-receiving elements 2a and 2b are not arranged at the same location, they are not completely common to each other, which causes a problem such as low measurement accuracy.

In view of the above points, the present invention aims to provide a near-infrared non-invasive living body measuring apparatus capable of measuring the oxygen state in a deep part of a living body with high accuracy by using near-infrared rays. .

[0009]

[Means for Solving the Problems]

 In order to achieve this object, a near-infrared non-invasive living body measuring apparatus according to claim 1 of the present invention includes a light-emitting element that irradiates near-infrared rays of two wavelengths with varying intensities, and this light-emitting element. And a light-receiving element that is placed at a fixed distance to receive the transmitted light due to the light, the light-emitting signal at each of the two wavelengths, and the light-receiving signal obtained by subtracting the light-receiving signal when the light intensity is strong or weak. And a control unit for calculating the oxygen states of a living body by calculating the absorbances of the above, and applying these absorbances to the bear Lambert's law.

[0010]

[Action]

 Therefore, according to claim 1 of the present invention, in the state where the light receiving element is arranged at a constant distance from the light source of the light emitting element, the near infrared light is emitted while changing its intensity to strong or weak. Thus, when the light intensity is high, a light reception signal is obtained by light that has passed through the entire body including the skull and cerebral cortex when the light intensity is low, and when light intensity is low, it is mainly due to light that has passed near the skull. A light reception signal is obtained. Since both the light source and the light receiving element are located at one place, the light receiving signals when the light intensity is weak can be accurately regarded as common in both the light source and the light receiving element.

Therefore, by subtracting the light reception signal when the light intensity is low from the light reception signal when the light intensity is high, the light reception signal due to the light passing through only the cerebral cortex can be obtained with high accuracy. Then, the actual absorbance of the cerebral cortex is calculated from the ratio of the light emission signal and the light reception signal at two wavelengths, and the oxygen saturation can be calculated by applying the parameters of these absorbances and the molecular extinction coefficient of hemoglobin to Bear Lambert's law. , The amount of hemoglobin is calculated with high accuracy.

[0012]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings. First, the measurement principle will be described with reference to FIG. When the near-infrared light source 1 and the light receiving element 2 are arranged on the surface of the skull, as the distance d from the light source 1 to the light receiving element 2 increases, the distance d decreases in inverse proportion to the square of the distance d. When the intensity of light is weak, the light m passes through a shallow part near the scalp of the skull and the skull, and as the intensity is higher, the light n reaches a deeper cerebral cortex. Then, if the distance d is the same, a light reception signal proportional to the intensity of the light source 1 is obtained.

Therefore, the light receiving element 2 is arranged only at one position at a predetermined distance d from the light source 1 to keep the distance d constant, and in this state, the light intensity of the light source 1 changes strongly and weakly. Then, when the light intensity is high, a light reception signal is obtained by the light n that passes through the entire deep place including the skull and the cerebral cortex, and when the light intensity is low, it mainly passes through a shallow place near the skull. A light reception signal by the light m is obtained. Since both the light source 1 and the light receiving element 2 are located at one location, it is possible to accurately consider that the light receiving signals in the areas near the light source 1 and the light receiving element 2 where the light intensity is weak and shallow are common.

Therefore, by subtracting the received light signal when the light intensity is low from the received light signal when the light intensity is high, it is possible to obtain the received light signal due to the light passing through only the cerebral cortex with high accuracy. . Therefore, it is only necessary to obtain the above-mentioned received light signal for each of two different wavelengths, and apply the bear Lambert's law to this to calculate the oxygen saturation and the like.

Next, an arithmetic expression such as oxygen saturation according to Bear Lambert's law will be described. First, letting the intensity of light incident on blood Io, the intensity of transmitted light from blood It, the molecular extinction coefficient ε of hemoglobin, the concentration of hemoglobin in tissue c, and the distance d from the light source to the light receiving element, (Equation 1) is established.

[0016]

[Equation 1]

When the ratio of incident light to transmitted light is the absorbance K, the absorbance K is represented by (Equation 2).

[0018]

[Equation 2]

Further, assuming that the oxygen saturation is SO ₂ , the molecular extinction coefficient HbO ₂ of oxygen hemoglobin, and the molecular extinction coefficient Hb of reduced hemoglobin, the extinction coefficient ε of hemoglobin is represented by (Equation 3).

[0020]

[Equation 3]

Therefore, the absorbance K becomes as shown in (Equation 4) according to (Equation 2) and (Equation 3).

[0022]

[Equation 4]

Further, since two wavelengths are used, assuming that the light absorbencies of the two wavelengths are K λ1 and K λ2, respectively, from (Equation 4), the absorbance K λ1 and K λ2 of each wavelength are given by the following (Equation 5) ) And (Equation 6).

[0024]

[Equation 5]

[0025]

[Equation 6]

Therefore, the oxygen saturation degree SO ₂ is calculated by (Equation 7) from (Equation 5) and (Equation 6).

[0027]

[Equation 7]

Further, the hemoglobin amount indexes c · d are represented by (Equation 8) from (Equation 5).

[0029]

[Equation 8]

Here, the molecular absorption coefficient HbO 2 of oxygen hemoglobin and the molecular absorption coefficient Hb of reduced hemoglobin can be experimentally obtained. Further, the actual absorbances Kλ1 and Kλ2 of the cerebral cortex of the skull can be calculated from the ratio of the light emission signal at each wavelength and the light reception signal obtained by changing the light intensity as described above. Therefore, the oxygen saturation S O ₂ of the cerebral cortex and the hemoglobin amount index c · d are calculated by putting these parameters in the formulas (7) and (8) and calculating them.

Referring to FIG. 2, an embodiment of the bioinstrumentation apparatus according to the present invention will be described. The apparatus main body 5 emits light and is connected to the sensor section 3 via the light receiving drive section 4 in a circuit. The sensor unit 3 includes, as the light source 1, two light-emitting elements 1a and 1b that emit near-infrared light having two wavelengths λ1 and λ2. The wavelengths λ1 and λ2 in this case are, for example, those shown in FIG. In the characteristics of the infrared absorption spectrum, the absorbances of oxygen hemoglobin and reduced hemoglobin are set to 803 nm, which is approximately the same, and 730 nm, which is smaller than that (if two different wavelengths are required). Two light receiving elements 2a and 2b such as photodiodes are arranged opposite to the two light emitting elements 1a and 1b at a constant distance d.

The apparatus main body 5 includes a control unit 7 such as a microcomputer driven by a power supply unit 6, and when a switch is operated by an operation unit 8, the control unit 7 emits light to instruct the light reception drive unit 4 to emit light and receive light. Then, the light of wavelengths λ1 and λ2 are output from the two light emitting elements 1a and 1b of the sensor unit 3 with the intensity changed to strong and weak, and the transmitted light of this light is output by the two light receiving elements 2a and 2b. Receive light respectively.

The light reception signals from the light receiving elements 2 a and 2 b are amplified by the amplification section of the light emission / reception drive section 4, the sample hold section 9 holds the amplified signal, and then converted into a digital signal by the A / D converter 12. And input to the control unit 7. The control unit 7 calculates the oxygen saturation SO _{2 and the} like in real time according to Bear Lambert's law based on the light emission signal, the light reception signal, etc., stores it internally, and displays it on the display unit 10, and when it exceeds a predetermined value. An alarm 11 is set to alert you.

A case of measuring the oxygen state of the cerebral cortex of the skull with the biometric device having the above configuration will be described. First, the two light emitting elements 1a and 1b and the light receiving elements 2a and 2b of the sensor unit 3 are attached in contact with the surface of the skull. After that, as shown in FIG. 3, the light emitting / receiving driving unit 4 outputs to the one light emitting element 1a a signal So H1 having a high light intensity and a signal SoL1 having a low light intensity as the light emission signal So1 to output the wavelength λ1. Irradiates light of 730 nm to the inside of the skull with intensity changed to strong and weak. Then, the light receiving element 2a receives the light n having a high intensity of light and transmitted through a deep place and the light m having a low intensity of light and transmitting through a shallow place, and a light reception signal when the intensity of light is high. StH1, and a weak light reception signal StL1 is obtained.

After that, the control unit 7 subtracts the light reception signal StL1 when the light intensity is low from the light reception signal StH1 when the light intensity is high. As a result, the light passes through only the cerebral cortex, and the received light signal St1 due to scattering and reflection mainly by hemoglobin of the blood is obtained with high accuracy. Then, the actual absorbance Kλ1 of the cerebral cortex when the wavelength λ1 is light of 730 nm is accurately calculated by calculating the ratio between the light emission signal So1 and the light reception signal S t1.

In addition, the other light emitting element 1b also outputs a signal SoH2 having a high light intensity and a signal SoL2 having a low light intensity as the light emission signal So2 to increase the intensity of the light having the wavelength λ2 of 803 nm. , Changes weakly and irradiates inside the skull. Then, the light n and m at the deep portion and the shallow portion transmitted through the skull are respectively received by the light receiving element 2b, and a light receiving signal StH2 when the light intensity is strong and a light receiving signal StL2 when the light intensity is weak are obtained. By subtracting these received light signals StH2 and StL2, the received light signal St2 resulting from light passing only through the cerebral cortex can be obtained with high accuracy as well. Then, the actual absorbance Kλ2 of the cerebral cortex when the wavelength λ2 is light of 803 nm is accurately calculated from the ratio of the light emission signal So2 and the light reception signal St2.

Therefore, the absorbances Kλ1 and Kλ2 of the cerebral cortex calculated as described above at the respective wavelengths λ1 and λ2, and the parameters of the molecular absorption coefficient HbO2 of oxygen hemoglobin and the molecular absorption coefficient Hb of reduced hemoglobin, which are obtained in advance by experiments, are set as follows. The oxygen saturation SO ₂ of the cerebral cortex and the hemoglobin amount index c · d are calculated in real time with high accuracy by putting the calculation into the above expression of Bear Lambert's law. The oxygen saturation SO ₂ and the hemoglobin amount index c · d are monitored on the display unit 10, and it is possible to check the oxygen state of the brain cells and the like by these values during surgery.

The embodiment of the present invention has been described above. However, since the light source and the light receiving section are provided at one place, it is possible to use one light receiving element.

[0039]

[Effect of device]

 As described above, in the near-infrared non-invasive living body measuring apparatus according to claim 1 of the present invention, a light-emitting element for irradiating near-infrared rays of two wavelengths with varying intensities, and this light-emitting element. A light receiving element that is placed at a fixed distance from the element and receives the transmitted light by that light, and a light receiving signal at each of the two wavelengths and a light receiving signal obtained by subtracting the light receiving signal when the light intensity is strong and when it is weak. It has a control unit that calculates actual absorbances and calculates the oxygen states of living organisms by adapting these absorbances to Bear Lambert's law. When the signal is weak, the received light signals can be accurately regarded as common. Therefore, by subtracting the received light signal when the light intensity is low from the received light signal when the light intensity is high, the received light signal due to the light passing through only the cerebral cortex can be obtained with high accuracy. It is possible to improve the measurement accuracy of the oxygen state at a deep place.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a measurement principle of a near-infrared non-invasive living body measuring device according to the present invention.

FIG. 2 is a circuit diagram of an embodiment of a near-infrared non-invasive living body measuring device.

FIG. 3 is a diagram showing two types of light emission signals having different wavelengths.

FIG. 4 is an explanatory diagram showing a conventional biometric method.

FIG. 5 is a diagram showing an absorption spectrum of near infrared rays.

[Explanation of symbols]

 1a light emitting element 1b light emitting element 2a light receiving element 2b light receiving element 7 control unit

Claims (1)

[Scope of utility model registration request] 1. A light-emitting element for irradiating near-infrared light of two wavelengths with varying intensities, and a light-receiving element arranged at a fixed distance from the light-emitting element and receiving transmitted light by the light. The actual absorbances are calculated from the light emission signals at the two wavelengths and the light reception signals obtained by subtracting the light reception signals when the light intensity is strong and when the light intensity is weak, and these absorbances are applied to Bear Lambert's law to determine the oxygen of the living body A near-infrared non-invasive living body measuring apparatus comprising: a control unit that calculates a state.