JP5917756B2 - Apparatus for measuring the relative concentration change and oxygen saturation of hemoglobin - Google Patents

Description

  The present invention relates to an apparatus for measuring a relative concentration change and oxygen saturation of hemoglobin in a living body, using non-invasive infrared rays.

  The supply of oxygen to the human body as a living body is carried and exchanged by circulating blood. Oxygen taken up by respiration is combined with hemoglobin (Hb) in the blood by gas exchange in the alveoli. Oxygen taken into the blood is sent to the whole body by arterial blood and taken up into cells by capillaries.

  Since the cells in each part are alive due to oxygen in the blood, it is necessary to constantly check the state of the brain cells by measuring the oxygen state of the skull, especially the cerebral cortex, in real time during surgery such as the heart It is. As a method of measuring the oxygen state of the cerebral cortex, a method of measuring non-invasively using near infrared rays having excellent tissue permeability is known.

  For example, a living body measuring apparatus described in Japanese Patent Application Laid-Open No. 2010-125147 (Patent Document 1) is known as an apparatus for simultaneously measuring information in the blood of a living body and physiological indices of the autonomic nervous system with high accuracy. In this apparatus, light incident means (LEDs) for injecting inspection lights having different center wavelengths and not incident on each other into a living body so that the incident period of the second inspection light is shorter than the incident period of the first inspection light. ) And photodetection means (photodiodes) that output digital signals corresponding to the light incident means, and the concentration change of oxyhemoglobin and deoxyhemoglobin is calculated based on the digital signal (output signal). And an arithmetic unit for calculating measurement data based on the digital signal.

  Moreover, as a device capable of monitoring a change in the residual oxygen amount at an abnormal site, there is a biological light measurement device described in Japanese Patent Application Laid-Open No. 2001-212115 (Patent Document 2). This apparatus includes a light irradiating means for irradiating a living body with light, a light detecting means for detecting light transmitted through the living body and outputting an electric signal corresponding to the detected light amount, and a hemoglobin concentration for each measurement site based on the electric signal. A signal processing means for calculating the signal and means for displaying the calculation result of the signal processing means, and the display means comprises means for displaying the time course of hemoglobin concentration for each measurement site. To do.

JP 2010-125147 A JP 2001-212115 A

  By the way, in the living body light measuring device described in Patent Document 1, since light having a central wavelength of 735 nm and light having a central wavelength of 850 nm are used as incident light, oxygen saturation can be mainly measured. However, the amount of hemoglobin cannot be compared. This is because, in order to measure a change in the amount of hemoglobin, light having a central wavelength of 800 to 810 nm must be used.

  Further, in Patent Document 2, it is possible to calculate a relative change amount of blood oxygenated hemoglobin / deoxygenated hemoglobin concentration for each measurement point. Although the amount of relative change at the time of measurement can be calculated along the time axis, the actual hemoglobin concentration at the time of measurement is unknown because it is based on the start of measurement.

  Conventionally, the degree of absorption of light of hemoglobin in a living body (light having an isoabsorption coefficient of oxy and deoxyhemoglobin of 805 nm) was measured, and the measured value was numerically displayed in an anonymous number. In both Patent Documents 1 and 2, the relative change amount is a relative value based on the measurement start time. In the conventional measurement method, since the subsequent change is measured with reference to the measurement start time, the change amount with respect to the concentration at the measurement start time can be measured, but the concentration at the measurement start time is unknown.

  The cerebral blood flow does not necessarily show the same value on the left and right sides of the cranium, but the left and right values are the same when the measurement start time is used as a reference. That is, even if there was a difference in blood flow between the left and right sides of the brain at the start of measurement, the difference could not be evaluated.

  Furthermore, in the conventional measuring apparatus, the signal of the sensor is detected by a photodiode. Regardless of the wavelength, the photodiode outputs light as long as it is in the sensitivity region. By the way, actual measurement is not performed in a dark environment. Therefore, even if it is desired to obtain only a signal based on desired light, external light is detected by the photodiode via the living body.

  Various methods for removing the external light have been proposed. For example, a method of modulating a signal to extract only the component or cutting using a filter is performed. However, it was not always possible to measure with sufficient accuracy.

  In view of these points, the present invention can measure hemoglobin concentration from the measurement start time point and subsequent temporal relative change, and can evaluate the difference in blood flow between the left and right sides of the brain. It is an object of the present invention to provide an apparatus for measuring relative concentration change and oxygen saturation. Another object of the present invention is to provide an apparatus for measuring the relative concentration change of hemoglobin and the oxygen saturation, which detects a signal of only desired light regardless of the measurement environment.

In order to achieve this object, a near-infrared non-invasive living body measurement apparatus according to claim 1 of the present invention comprises a sensor part and an apparatus main body part. A light receiving element that receives light transmitted from a light source and a ROM unit that records a reference value related to transmitted light measured in advance using a phantom capable of obtaining the same absorption characteristics as a living body. The unit includes an arithmetic processing unit that calculates an actual absorbance based on a light reception signal of the sensor unit, and calculates the oxygen state of the living body in accordance with Bare Lambert's law in comparison with the reference value. To do.

  The phantom includes a separately formed phantom and a measuring device including a sensor unit and a device main body. The phantom has a cushioning material in a lowermost layer in a box-shaped case formed of a material that completely blocks light. It is formed by sequentially laminating a reflecting plate, a scattering layer, an absorbing plate, a scattering layer, and an absorbing plate thereon, and the sensor unit includes a light source and a light receiving element disposed at a certain distance from the light source, It consists of a ROM that records the received light signal of the phantom as a reference value, and the device main unit calculates the actual absorbance based on the received light signal of the sensor unit, and compares it with the reference value to adapt to Bear Lambert's law. It is good also as a structure provided with the arithmetic processing part which calculates the oxygen state of a biological body.

The sensor unit includes a ROM that records a reference value related to transmitted light measured in advance using a phantom capable of obtaining the same absorption characteristics as a living body, thereby changing the relative concentration of hemoglobin in the blood at the start of measurement and the degree of oxygen saturation. Can be provided as a relative value compared to the reference value. That is, by using the phantom as a reference, a comparison based on an absolute value rather than a relative value based on the measurement start time can be performed.

  Further, by using the absolute value by the phantom as a reference, the difference between the left and right blood flow in the skull can be found. Conventionally, changes after the start of measurement can be evaluated, but since the measurement start time is the reference for both the left and right sides of the skull, the difference in blood flow between the left and right cannot be evaluated. Furthermore, the sensor error can be corrected by using the phantom as a reference. Individual sensors are manufactured to show the same standard measurements, but in practice there are slight errors. Therefore, even if there is an error in each sensor, by using the phantom as a reference, the error can be corrected for all the sensors and a reference value of the same level can be provided.

It is a block diagram which shows the structure of the measuring apparatus which concerns on this invention. It is a schematic explanatory drawing which shows the structure according to the type of sensor. It is a longitudinal cross-sectional view which shows the structure of a phantom. It is a circuit diagram in the amplifier part of the apparatus main body part.

  Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 shows a block diagram of the present measuring apparatus. The measuring apparatus 1 includes a sensor part 2 and an apparatus main body part 3 that are mounted on the surface of the skull. The sensor unit 2 includes light sources 11 and 12 using LEDs and light receiving elements 11A and 12A formed of photodiodes. The light source 11 measures the left side, the light receiving element 11A, and the light source 12 measures the right side. The light receiving elements 12A are arranged in pairs on the left and right.

  In the illustrated embodiment, a double type in which the left and right are paired is shown, but a single type divided into a left side light source 11 and a light receiving element 11A, and a right side light source 12 and a light receiving element 12A divided at the center part. (See FIG. 2). In the case of a single type, they may be attached to the left and right individually.

  The light sources 11 and 12 are composed of LEDs, project near-infrared rays to the monitor site 10 times per second at a wavelength of 0.2 mSec, and the photodiodes of the light receiving elements 11A and 12A are oxyhemoglobin, deoxyhemoglobin, and Near-infrared rays of each wavelength corresponding to these cross points are detected, the signals are amplified, and measured values are calculated. For example, the wavelengths of the light sources 11 and 12 are set to 805 nm at which the absorbances of oxygen hemoglobin and reduced hemoglobin substantially coincide with each other, 770 nm which is smaller than that, and 870 nm which is larger than that in the near infrared absorption spectrum characteristics.

  When the near-infrared light sources 11 and 12 and the light receiving elements 11A and 12A are mounted on the surface of the cranium, the distance from the light source 11 to the light receiving element 11A and from the light source 12 to the light receiving element 12A increases in inverse proportion to the square of the distance d. Then decrease. In addition, when the intensity of light is weak, the light passes through a shallow area near the skull and skull of the skull, and the stronger the intensity, the deeper the light reaches the cerebral cortex. If the distances are the same, a light reception signal proportional to the intensity of the light sources 11 and 12 is obtained.

  2 and Table 1 show the relationship between the distance between the light source 11 and the light receiving element 12 of the sensor 2 and the depth (monitor depth) through which light passes.

  2A shows a single type composed of a light source 11 and a light receiving element 11A, and FIG. 2B shows a double type in which the light source 11, the light receiving element 11A, the light source 12, and the light receiving element 12A are arranged in pairs. Is shown. The distance between the light source and the light receiving element is determined by the size of the skull for adults, middle-aged (children to adults), and children.

  In FIG. 1, the ROM 4 in the sensor unit 2 contacts the sensor 2 with the phantom 5 shown in FIG. 3, measures the reflected light, reads the signal, and records and stores it as calibration data. It is read at startup and becomes the reference value at the start of measurement. Since the output and time of the sensor unit 2 are controlled so that the heat of light is washed out in the bloodstream, calibration before measurement is not necessary.

  Next, the configuration of the phantom 5 serving as calibration data will be described with reference to FIG. The phantom 5 is formed by stacking a scattering plate or the like in a box-shaped case 51 made of a material that completely blocks light. More specifically, a sponge rubber sheet is laid as the cushioning material 52 at the bottom layer, an aluminum plate is placed thereon as the reflecting plate 53, and five acrylic plates having a thickness of 2 mm are laminated as the scattering layer 54, and then Further, a gray PVC plate having a thickness of 0.4 mm as the absorbing plate 55 and six acrylic plates having a thickness of 2 mm as the scattering layer 54 are laminated, and a 0.4 mm thick gray plate is formed as the absorbing plate 55 on the uppermost surface. It is formed by laminating PVC plates.

  The phantom 5 having the above configuration can obtain the same absorption characteristics as a living body by adjusting the position of the absorption plate 55 laminated in the middle. Although the light receiving characteristics of the sensor and the absorption characteristics of the vinyl chloride plate differ depending on the wavelength, the thickness of the phantom 5 of the embodiment is formed to be about 23 mm because the light receiving element is approximately flat at a depth of 20 mm at a distance of 40 mm.

  If the absorbance is obtained at a wavelength (805 nm) having the same extinction coefficient for oxy and deoxyhemoglobin, the absorbance is correlated with the change in the hemoglobin regardless of the value of the oxygen saturation, and this is expressed as the hemoglobin index (HbI). ). The hemoglobin index is an anonymous number and is a relative value. In the conventional apparatus, the change is compared on the basis of the measurement start or a certain time point during the measurement. However, since the phantom 5 is used as a reference, the relative change can be compared from the measurement start time.

Sensor signals are detected by the light receiving elements 11A and 12A (photodiodes). Regardless of wavelength, the photodiode outputs a signal as long as it is in the sensitivity region.
In actual measurement, measurement is not performed in a dark environment. Even if it is desired to obtain only a desired light signal, external light is detected by a photodiode via a living body.

  Various methods for removing the external light have been proposed. For example, the signal is modulated to extract only the component, or is cut using a filter. In this invention, a period of no light (blank) in which light of a desired wavelength is not lit is provided, and the output of the photodiode at the time of no light (only surrounding light) is measured (sample hold) and held, A signal of only the desired light is obtained as data by subtracting the value of only the ambient light from the value of the light detected as the sum of the desired light and the ambient light when the desired light is lit in the electronic circuit. It was.

  By using the above calculation method, the conventional complicated signal processing is unnecessary, and the measured value when the desired light shines is the increment of the baseline regardless of whether the surrounding environment is bright or dark. Measurement can be performed regardless of the surrounding environment.

  Since the sensor unit 2 in FIGS. 1 and 2 is attached to the forehead portion, the surrounding light that has passed through the skin, skull, etc. around the sensor is affected, but the level of the signal due to the surrounding light is determined by the light receiving element. Since the saturation level is not reached, the influence of surrounding light can be ignored.

  Furthermore, the following effects can be obtained by using a phantom. That is, each sensor is manufactured to maintain the same performance, but there is a slight error in the actual product. Since all the conventional sensors are based on the measurement start time, the error is not corrected. In this invention, since the reference of the measurement start time is obtained from the phantom, each sensor can be the reference.

  If a measurement sensor with a built-in calibration value based on the phantom is used, the measured value on the phantom will be 50% oxygen saturation and 1.0 hemoglobin. For example, when Mr. A is measured with this sensor, the oxygen saturation may be 63% on the left, 62% on the right, the amount of hemoglobin may be 1.2 on the left, and 0.8 on the right. In the conventional measurement method, since hemoglobin is 1.0 at the start of measurement, the left and right are 1.0, and the left and right cannot be recognized as a difference.

  Next, the configuration of the apparatus main body 3 will be described. The apparatus main body 3 is connected to the sensor unit 2 in a circuit, and is connected to a power unit 31, a power control unit 31a for controlling the voltage of the power unit 31, an amplifier unit 32 for amplifying measurement data, and digital so that data can be calculated. An A / D converter 33 for converting to a signal, an arithmetic processing unit 34 for calculating data, a screen display unit 35 for displaying data, a memory unit 36 for recording data, and LEDs of the light sources 11 and 12 of the sensor unit are driven and controlled. The LED driving unit 37, a clock unit 38 for synchronizing signals, an input unit 39 for external operation, and a USB output unit 34a for outputting data to the outside.

  When the power supply unit 31 is switched, the apparatus body 3 instructs the LED drive unit 38 to emit light and receive light by the arithmetic processing unit 34. Then, light of a predetermined wavelength is output from the two light sources 11 and 12 of the sensor unit 2 with the intensity changed between strong and weak, and the transmitted light of the light is received by the two light receiving elements 11A and 12A, respectively. To do.

  Light reception signals by the light receiving elements 11A and 12A are amplified by the amplifier unit 32, and the amplified signal is converted into a digital signal by the A / D converter unit 33 and input to the arithmetic processing unit 34. The arithmetic processing unit 34 calculates the oxygen saturation rSO2 and the like in real time according to Bare Lambert's law from these light emission signals, light reception signals, and the like, stores them in the memory unit 36, and displays them on the screen display unit 35.

  A case where the measuring apparatus having the above configuration is used will be described. First, the two light sources 11 and 12 and the light receiving elements 11A and 12A of the sensor unit 2 are mounted in contact with the surface of the skull. Thereafter, a light signal is output to the light sources 11 and 12 to irradiate the inside of the skull. Then, the light transmitted through the skull is received by the light receiving elements 11A and 12A, respectively. A light reception signal obtained by scattering and reflecting the blood mainly by hemoglobin is required with high accuracy. Thereafter, arithmetic processing is performed in the arithmetic processing unit.

  The measuring apparatus 1 irradiates the skull with near-infrared light, and the amount of absorbed light is proportional to the concentration of incident light and solute. According to the Lambert-Beer law, the oxygen saturation level of hemoglobin in the brain region And measure changes in concentration. Using the difference in light absorption spectrum between oxyhemoglobin and deoxyhemoglobin, the absorbance is obtained from the light detected by the light receiving element through the skull at different wavelengths (770 nm and 870 nm), and the local oxygen saturation (rSO2 ).

  In the arithmetic processing unit 34, the oxygen saturation is calculated as follows. If the absorbance of oxyhemoglobin is KHbO2, the absorbance of deoxyhemoglobin is KHb, the oxygen saturation is rSO2 = HbO2 / (HbO2 + Hb), the optical path length is d, and the solute concentration is C, the absorbance K directly below the sensor at a certain wavelength. Since the superposition theory holds, the following equation 1 is obtained.

  Absorbance is calculated from detection signals at two wavelengths (assuming R770 nm and IR870 nm), and the ratio is obtained by Equation 2.

  Since this R / IR correlates with the oxygen saturation, the oxygen saturation and the amount of hemoglobin in the blood sample in the test tube are measured in advance to make them known, and the R / IR of the blood sample is measured. Based on the R / IR value obtained by this measurement and the oxygen saturation of the blood measured by the measuring device 1, a calibration curve showing the relationship between R / IR and oxygen saturation is prepared, and the unknown The oxygen saturation (rSO2) is calculated and displayed from the measured light absorption ratio R / IR.

Next, a circuit diagram of the amplifier unit 32 of the apparatus body 3 will be described with reference to FIG. In FIG. 4, an analog signal detected by a photodiode (PD) is input to pin number 2 of U5.
A timing clock for holding each signal is input to pin number 8 of U9, U12, U13, U16, U17, U20, and U21, and light emission detected by a photodiode (PD) in synchronization with the clock of the clock unit 37. A signal for each wavelength is held and output to the pin number 5 as a DC voltage.

  The output DC voltage is converted into a digital signal by the A / D converter unit 33, is subjected to arithmetic processing by the arithmetic processing unit 34, and is provided as information on oxygen saturation and hemoglobin amount. The above circuit is characterized in that the signal level when there is no light is held and applied at U20 to the reference pin 2 of the differential amplifier U8, so that the output of U8 is the difference from the input signal.

  As described above in detail, since the measurement value excluding the external brightness is obtained, the measurement value is not limited to indoor use such as an operating room, and can be used without being affected by the measurement environment such as a disaster site or day and night.

1: Measuring device 2: Sensor unit 3: Device body unit 5: Phantom 11, 12: Light source 11A, 12A: Light receiving element 31: Power supply unit 32: Amplifier unit 33: A / D converter unit 34: Arithmetic processing unit 35: Screen Display unit 36: Memory unit 37: Clock unit 38: LED drive unit 39: Input unit

Claims (2)

It consists of a sensor part and a device body part. The sensor part has a light source that irradiates near infrared rays, a light receiving element that is arranged at a certain distance from the light source and receives transmitted light from the light source, and the same absorption characteristics as a living body And a ROM part that records a reference value relating to transmitted light measured in advance using a phantom that can be obtained , and the apparatus main body part calculates an actual absorbance based on a light reception signal of the sensor part and compares it with the reference value. An apparatus for measuring a change in the relative concentration of hemoglobin and an oxygen saturation level, comprising an arithmetic processing unit that calculates the oxygen state of a living body in conformity with Bear Lambert's law. It consists of a phantom, a measuring device equipped with a sensor unit and a device main body, and the phantom lays a cushion material on the lowermost layer in a box-shaped case made of a material that completely blocks light, and on it A reflection plate, a scattering layer, an absorption plate, a scattering layer, and an absorption plate are sequentially laminated. The sensor unit includes a light source, a light receiving element disposed at a certain distance from the light source, and a light reception signal of the phantom. The apparatus body unit calculates the actual absorbance based on the light reception signal of the sensor unit, and adapts to the Bare Lambert law in comparison with the reference value to determine the oxygen state of the living body. A device for measuring a relative concentration change of hemoglobin and an oxygen saturation measuring device, comprising an arithmetic processing unit for calculating

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