Oxygen saturation measurement device, a probe configured to be used therein, and oxygen saturation measurement method

Abstract

To provide an oxygen saturation measuring device capable of safely, easily and economically measuring arterial blood oxygen saturation (SpO2) and tissue oxygen saturation (rSO2) at a desired position of a biological body continuously for a long time.SOLUTION: A ROM stores distance information between a light emitting unit and a light receiving unit positioned corresponding to depth of a measurement target of tissue oxygen saturation, a light emission driving unit causes the light emitting unit to emit light with a light amount corresponding to the distance information, and an MPU causes the light emitting unit to emit a pulse capable of measuring the tissue oxygen saturation. The MPU applies the pulse capable of measuring the tissue oxygen saturation from the light emission driving unit to the light emitting unit, and a pulse increasing unit increases a pulse amount from the MPU for a predetermined time to a pulse capable of measuring arterial blood oxygen saturation.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] This application claims the priority of U.S. Non-Provisional Patent Application No. 16 / 746,208, filed on January 17, 2020, entitled "Oxygen Saturation measuring Device, Probe Adapted To Be Used Therefor, And Oxygen Saturation measuring Method", the entire content of which is incorporated herein by reference.

[0002] The present invention relates to an oxygen saturation measuring device, a probe configured to be used therefor, and an oxygen saturation measuring method, and more particularly, to an oxygen saturation measuring device that measures near-infrared light emitted from a light emitting unit to a living body and received by a light receiving unit, a probe configured to be used therefor, and an oxygen saturation measuring method.

Background Art

[0003] Conventionally, a pulse oximeter is known as a medical device that can measure arterial oxygen saturation (hereinafter referred to as "SpO2") and pulse rate by attaching a detector called a probe (see, for example, Japanese Patent Application Laid-Open No. 2019-48050).

[0004] Oxygen is supplied to the human body by the blood circulating in the body. Oxygen taken in from the lungs by respiration binds to hemoglobin contained in the blood and is transported throughout the body. A pulse oximeter is configured to measure the ratio of hemoglobin bound to oxygen among the hemoglobin contained in the blood flowing through the arterial blood transported from the heart to the whole body.

[0005] The probe of a pulse oximeter includes a light emitting unit that emits light, that is, two types of near-infrared light having different wavelengths, and a light receiving unit that detects the light emitted from the light emitting unit on the side opposite to the light emitting unit. The two types of light emitted from the light emitting unit pass through a fingertip, an earlobe, etc., and the light receiving unit measures the transmitted light on the opposite side.

[0006] Since the amount of light absorbed by hemoglobin contained in the blood differs for two types of light depending on the binding state with oxygen, by measuring the light transmitted through or reflected from the fingertip or earlobe with a light receiving unit and further analyzing the difference in the amount of light absorption of the two types of light, SpO2 can be measured.

[0007] The light radiated onto a living body, such as a fingertip or earlobe, passes through tissue layers other than blood, an arterial layer, and a venous layer, and reaches a light receiving unit that detects the light while receiving light absorption in each layer. Furthermore, the arterial blood sent out from the heart and carried throughout the body by pulsation moves within the blood vessels by tracing a waveform called a pulse wave due to changes in blood pressure or volume within the peripheral vascular system.

[0008] Only the pulsating arterial blood changes in thickness by a pulse wave in an extremely short time, and the thickness does not change in tissue layers other than blood and the venous layer. Since the amount of transmitted light also changes with the change in thickness, the light detected by the light receiving unit also changes. Therefore, the light amount fluctuation component detected by the light receiving unit is information on the thickness change part, that is, arterial blood.

[0009] By removing the unchanged part from the pulse wave and analyzing the change component, the change component of arterial blood can be measured. Furthermore, by analyzing the change components of the two types of light during radiation, SpO2 as the oxygen saturation of only arterial blood can be measured.

[0010] Therefore, a pulse oximeter can simultaneously measure SpO2 and pulse rate and can be used to evaluate the oxygen exchange function of the lungs. On the other hand, SpO2 cannot be measured at a site where arterial pulsation cannot be detected.

[0011] By the way, in the case of heart surgery, it is always necessary to measure the oxygen state within brain cells, specifically in the cerebral cortex, in real time to confirm the state of the brain. However, the existing pulse oximeters described above cannot measure the oxygen state of the cerebral cortex.

[0012] When measuring SpO2 by attaching the probe of a pulse oximeter to a fingertip or earlobe, since the distance between the light-emitting unit and the light-receiving unit is short, the light emitted from the light-emitting unit travels straight through the tissue of the fingertip or earlobe and is transmitted to the light-receiving unit, and SpO2 can be measured based on the amount of absorption of that light.

[0013] By the way, the cerebral cortex is a thin layer of nerve cells extending on the surface of the brain, and the cerebral cortex is covered with the scalp, skull, cerebrospinal fluid, etc. Therefore, even if one tries to measure the oxygen state in the cerebral cortex with a pulse oximeter, the light emitted from the light-emitting unit is scattered or diffused due to the presence of obstacles such as the scalp, skull, and cerebrospinal fluid, so the light-receiving unit cannot receive light accurately, and the oxygen state in the cerebral cortex cannot be measured accurately.

[0014] Therefore, a tissue oxygen saturation measuring device has been provided that can measure tissue oxygen saturation (hereinafter referred to as "rSO2") by setting a probe at a desired position, for example, on the forehead, like a pulse oximeter (see, for example, Japanese Patent Application Laid-Open No. 2006-75354).

[0015] The probe configured for use in a tissue oxygen saturation measuring device includes a light-emitting unit that emits two types of near-infrared light with different wavelengths, and a light-receiving unit that receives the light emitted from the light-emitting unit. The probe is attached to a desired position such as the forehead in a state where the light-emitting unit and the light-receiving unit are fixed at a predetermined distance on the same plane and directed in the same direction. By setting the probe at a desired position such as the forehead, having the light-receiving unit receive the two types of light emitted from the light-emitting unit, and analyzing the received light, rSO2 can be measured.

[0016] In a tissue oxygen saturation measuring device, since the tissue oxygen saturation is calculated by arithmetic means for all the light received by the light-receiving unit, the measured oxygen saturation is the oxygen saturation of the entire blood contained in the peripheral blood vessels of the target tissue, and the oxygen saturation measured by the tissue oxygen saturation measuring device generally shows a measured value containing 25% of the arterial component and 75% of the venous component.

[0017] Since the rSO2 measured by the tissue oxygen saturation measuring device contains a lot of information on venous blood after oxygen is transmitted to the tissue through capillaries, it is used to evaluate whether the tissue is sufficiently supplied with oxygen and whether oxygen metabolism is proceeding normally. In particular, it is an important indicator for evaluation during cardiac surgery or for evaluating the cerebral oxygen state of a cardiac arrest patient. On the other hand, since the tissue oxygen saturation measuring device does not detect much arterial information, it cannot accurately measure the pulse or SpO2.

[0018] The above-described pulse oximeter and tissue oxygen saturation measuring device both measure oxygen saturation, but because their measurement targets are different, in the medical field, they are selectively used, or used arbitrarily in parallel, according to the value to be measured.

Prior Art Documents

Patent Documents

[0019]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0020] However, each of the devices such as a pulse oximeter and a tissue oxygen saturation measuring device also has its own problems. First, the pulse oximeter has a problem of causing low-temperature burns when measuring SpO2 using the probe for a long time.

[0021] Since the change in thickness due to the pulse wave occurs in an extremely short time, in order for the pulse oximeter to detect the pulse wave, it is necessary for the light emitting unit to irradiate the tissue with light at a pulse rate of 30 / second or more.

[0022] Since the light emitted from the light-emitting unit is near-infrared light, i.e., heat rays, when continuously measuring SpO2 at the same site with a pulse oximeter, low-temperature burns are caused by the accumulation of heat due to the near-infrared light. Therefore, in a pulse oximeter, long-time probe setting at the same site is defined as a taboo or prohibited matter.

[0023] In order to prevent low-temperature burns during SpO2 measurement with a pulse oximeter, it is necessary to periodically change the probe setting position. However, for this purpose, reliable management for changing the setting time and setting position is required, which takes time and may increase the human cost.

[0024] On the other hand, a tissue oxygen saturation measuring device has a problem that it takes a lot of time to set the light emission amount from the light-emitting unit according to the site of the target tissue. Specifically, in the probe used in the tissue oxygen saturation measuring device, since the light-emitting unit and the light-receiving unit are located at a predetermined distance, the distance between the light-emitting unit and the light-receiving unit must be set to 1.25 to 1.5 times the depth from the epidermis where the probe is set.

[0025] The oxygen saturation of the target tissue is measured by a probe in which the light-emitting unit and the light-receiving unit are arbitrarily located at a distance corresponding to the measurement target tissue. If the amount of light emitted from the light-emitting unit is excessive with respect to the depth at which the measurement target tissue exists, a phenomenon similar to halation in a photograph occurs, where the periphery of the subject becomes blurred and unclear due to the excessive amount of light, and the change in hemoglobin oxygen saturation cannot be measured.

[0026] In order to accurately measure the oxygen saturation of the target tissue without causing such halation, since there is an arbitrarily selectable light absorption amount with respect to the distance between the light-emitting unit and the light-receiving unit, it is necessary to control the light emission amount from the light-emitting unit so that the change in the oxygen saturation of hemoglobin can be measured with respect to the depth of the measurement target tissue from the epidermis, that is, the distance between the light-emitting unit and the light-receiving unit.

[0027] When the tissue to be measured is at a deep position from the epidermis, it is necessary to increase the amount of light radiated from the light-emitting unit. On the other hand, when the tissue to be measured is at a shallow position from the epidermis, if the amount of light radiated from the light-emitting unit is not reduced, halation will occur and it will be impossible to measure the change in oxygen saturation of hemoglobin.

[0028] Conversely, when the tissue to be measured is at a deep position from the epidermis, if the amount of light radiation from the light-emitting unit is small, the light-receiving unit cannot accurately receive light, and the change in oxygen saturation of hemoglobin cannot be measured.

[0029] In addition, when the distance between the light-emitting unit and the light-receiving unit varies depending on the depth of the tissue to be measured, the loss rate of light varies due to light scattering or diffusion, so it takes a considerable amount of time to perform accurate light quantity control.

[0030] In the medical field, there are cases where the SpO2 or rSO2 of a patient has to be measured for a long time. In such cases, the above-mentioned pulse oximeter for SpO2 measurement cannot accurately measure rSO2, while the tissue oxygen saturation measuring device for rSO2 measurement cannot accurately measure SpO2. Therefore, a pulse oximeter for SpO2 measurement and a tissue oxygen saturation measuring device for rSO2 measurement have to be prepared separately, which incurs a lot of installation costs.

[0031] The present invention has been made in view of such points, and provides an oxygen saturation measuring device that can safely, easily and economically continuously measure arterial blood oxygen saturation (SpO2) and tissue oxygen saturation (rSO2) at a desired position of a living body for a long time, and a probe configured to be used therefor.

Means for Solving the Problems

[0032] In order to solve the above problems, the present invention provides an oxygen saturation measuring device that measures the oxygen saturation of a living body by measuring near-infrared light radiated from a light-emitting unit toward the living body and received by a light-receiving unit. The oxygen saturation measuring device includes: An information storage device provided corresponding to the depth of the measurement target of tissue oxygen saturation and storing distance information between a light emitting unit and a light receiving unit, A light emission drive unit for radiating light to the light emitting unit with a light quantity corresponding to the distance information, A pulse output unit for outputting a pulse capable of measuring tissue oxygen saturation, and a pulse increase unit that increases the rate of the pulse from the pulse output unit for a predetermined time to enable measurement of arterial blood oxygen saturation.

[0033] Thus, the information storage device stores information related to the distance between the light emitting unit and the light receiving unit provided corresponding to the depth of the measurement target of tissue oxygen saturation, the light emission drive unit drives the light emitting unit to emit light by an amount of light corresponding to the distance information, the pulse output unit causes the light emitting unit to emit a pulse capable of measuring tissue oxygen saturation, and the pulse increase unit increases the amount of the pulse from the pulse output unit for a predetermined time to a pulse capable of measuring arterial blood oxygen saturation.

[0034] Furthermore, the present invention provides a probe configured to be used in an oxygen saturation measurement device that measures near-infrared light radiated from a light emitting unit toward a living body by a light receiving unit, and the probe includes: an information storage device provided corresponding to the depth of the measurement target of tissue oxygen saturation and storing information regarding the distance between the light emitting unit and the light receiving unit, a light emission drive unit that causes the light emitting unit to emit light with a light quantity corresponding to the information regarding the distance, a pulse output unit for causing the light emitting unit to emit light with a light quantity corresponding to the information regarding the distance, and includes.

[0035] In this way, the information storage device stores distance-related information of the light-emitting unit and the light-receiving unit provided corresponding to the depth of the measurement target of tissue oxygen saturation, the light-emitting drive unit drives to emit light to the light-emitting unit with a light amount corresponding to the distance-related information, and the pulse output unit applies a pulse capable of measuring tissue oxygen saturation to the light-emitting unit.

[0036] Furthermore, the present invention provides an oxygen saturation measurement method for measuring the oxygen saturation in a living body by measuring, with a light-receiving unit, near-infrared light applied from a light-emitting unit to the living body. The method includes: a step of storing distance-related information between a light-emitting unit and a light-receiving unit provided corresponding to the depth of the measurement target of tissue oxygen saturation; a step of emitting light from the light-emitting unit with a light amount corresponding to the distance-related information by a light-emitting drive unit; a step of applying, by a pulse output unit, a pulse capable of measuring tissue oxygen saturation to the light-emitting unit; and a step of increasing, by a pulse increasing unit, the amount of pulses from the pulse output unit to a pulse capable of measuring arterial blood oxygen saturation for a predetermined time.

[0037] In this way, the information storage device stores distance-related information (hereinafter, may also be referred to as distance information) of the light-emitting unit and the light-receiving unit provided at a distance corresponding to the depth of the measurement target of tissue oxygen saturation. The light-emitting drive unit causes the light-emitting unit to emit light with a light amount corresponding to the distance-related information, the pulse output unit applies a pulse capable of measuring tissue oxygen saturation to the light-emitting unit, and the pulse increasing unit increases the amount of pulses from the pulse output unit to a pulse capable of measuring arterial oxygen saturation for a predetermined time.

[0038] According to the oxygen saturation measuring device, probe, and oxygen saturation measuring method of the present invention, since the information storage device stores the distance information between the light emitting unit and the light receiving unit provided corresponding to the depth of the measurement target of tissue oxygen saturation, the light emission driving unit radiates light to the light emitting unit with an amount of light corresponding to the distance information, the pulse output unit radiates a pulse capable of measuring the tissue saturation of the measurement target to the light emitting unit, and the pulse increasing unit increases the amount of pulses from the pulse output unit to a pulse capable of measuring arterial blood oxygen saturation for a predetermined time. Therefore, the accumulation of heat in the tissue due to near-infrared light is alleviated, and both SpO2 and rSO2 can be measured with a single device. Thus, it becomes possible to safely, easily, and economically continuously measure arterial blood oxygen saturation (SpO2) and tissue oxygen saturation (rSO2) at a desired position in a living body for a long time.

Brief Description of the Drawings

[0039]

Figure 1A

Figure 1B

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0040] A preferred embodiment of the present invention will be specifically described with reference to the drawings. FIGS. 1A and 1B are block diagrams showing the overall configuration of an oxygen saturation measuring device (hereinafter sometimes also referred to as a system) according to the present invention. As shown in FIGS. 1A and 1B, the oxygen saturation measuring system 100 includes a probe 110, a device main body 120, a terminal device 130, and a display 140.

[0041] The probe 110 is configured to be set on a living body to obtain information on a target tissue so that the information obtained by the device main body 120 can be digitized and sent to the terminal device 130.

[0042] The device main body 120 is configured to operate the probe 110 by sending a signal to the probe 110 and relay the digital signal obtained from the probe 110 and send it to the terminal device 130.

[0043] The terminal device 130 is configured to perform arithmetic processing such as calculating the oxygen saturation of the target tissue measured by the probe 110 based on the information obtained from the target tissue via the device main body 120 in order to store the result.

[0044] The display 140 is a monitor connected to the terminal device 130 and configured to display information on the oxygen saturation calculated by the terminal device 130, graphs, etc. Further, the display 140 can also display a menu screen or the like for selecting an instruction for operating the probe 110 or the device main body 120.

[0045] Furthermore, the oxygen saturation measuring system 100 can perform measurement of the oxygen saturation of the target tissue, processing of measurement data, control such as startup and termination of the system, and power supply to the probe 110, the device main body 120, etc. by operations using the terminal device 130 and the display 140.

[0046] Probe 110 is a detector configured to measure the oxygen saturation of a target tissue for the purpose of obtaining information, which is set on a part of a living body and includes a light emitting unit 111, a light receiving unit 112, a light emission driving unit 113, a light receiving amplifier 114, an analog-to-digital converter 115 (hereinafter also referred to as A / D converter 115), an MPU (microprocessing unit) 116, a ROM (read only memory) 117 (hereinafter also referred to as an information storage unit), and a UART (universal asynchronous receiver / transmitter) 118.

[0047] The light emitting unit 111 is configured to obtain information on a target tissue by applying light as a plurality of types of near-infrared light to a living body, and includes, for example, a near-infrared light emitting diode with three wavelengths as a light source for light emission.

[0048] The near-infrared light emitting diodes with three wavelengths of the light emitting unit 111 are, for example, near-infrared light emitting diodes with wavelengths of 770 nm, 805 nm, and 870 nm. Such near-infrared light emitting diodes are respectively connected to the light emission driving unit 113.

[0049] The light receiving unit 112 is configured to detect the light emitted from the light emitting unit 111 and is respectively connected to the light receiving amplifier 114. The light receiving unit 112 is, for example, a photodiode and can output the light in its sensitivity region as a signal regardless of the wavelength of the light emitted from the light emitting unit 111.

[0050] The light emitting unit 111 and the light receiving unit 112 are provided at a predetermined distance, and it is possible to measure the change in hemoglobin in a target tissue located at a depth within 70% to 80% of the distance corresponding to the distance between the light emitting unit 111 and the light receiving unit 112.

[0051] A plurality of probes 110 with an arbitrarily selectable distance between the light-emitting unit 111 and the light-receiving unit 112 are each provided, and a desired probe 110 can be selected and used from among them according to the position of the target tissue to be measured. Further, the light-emitting unit 111 needs to emit an appropriate amount of light with respect to the distance between the light-emitting unit 111 and the light-receiving unit 112. The control method will be described later.

[0052] The light-emitting drive unit 113 is configured to cause the light-emitting unit 111 to emit light, and includes, for example, a transistor that controls a current for causing a near-infrared light-emitting diode to emit light at a constant current, and is connected to the light-emitting unit 111 and the MPU 116.

[0053] The light-emitting unit 111 can emit a larger amount of intense light by increasing the current supplied from the light-emitting drive unit 113, and can send the light to the target tissue deep inside the living body.

[0054] The light-receiving amplifier 114 is configured to amplify the received optical signal detected by the light-receiving unit 112 to a required signal level, and is connected to the light-receiving unit 112 and the A / D converter 115.

[0055] The A / D converter 115 is configured to convert an analog signal into a digital signal, and is connected to the light-receiving amplifier 114 and the MPU 116. The light-receiving amplifier 114 amplifies the received optical analog signal detected by the light-receiving unit 112, and the A / D converter converts the amplified received optical analog signal into a digital signal.

[0056] In the prior art, the light emitted from the light-emitting unit 111 is received by the light-receiving unit 112 and amplified by the light-receiving amplifier 114, and the light-receiving amplifier 114 transfers a low-voltage analog signal amplified by the light-receiving amplifier 114 to a terminal device or the like disposed several meters away via a communication cable.

[0057] By the way, since an analog signal with a low voltage is susceptible to external noise, the measured value becomes unstable. Therefore, in the present invention, the light emitted from the light-emitting unit 111 is received by the light-receiving unit 112, the analog signal amplified by the light-receiving amplifier 114 is amplified to a necessary signal level, and immediately thereafter, the A / D converter 115 converts the analog signal into a digital signal.

[0058] Therefore, it is possible to transmit the stable signal converted by the A / D converter 115 as a digital signal without transmitting the analog signal susceptible to external noise through the communication cable.

[0059] The MPU 116 is a microprocessor for controlling each connected device, and is connected to the light-emitting drive unit 113, the A / D converter 115, and the ROM 117. For example, the light-emitting drive unit 113 causes the light-emitting unit 111 to emit pulsed light in synchronization with the clock pulse from the MPU 116.

[0060] The ROM 117 is an information storage device for storing information. For example, the ROM 117 stores calibration data for the output of the light-receiving amplifier 114, which is a coefficient for calibrating the output of the light-receiving amplifier 114 so that the signal levels of the analog signals output from the light-receiving amplifier 114 are equal to each other.

[0061] The light-emitting unit 111 may include a plurality of near-infrared light-emitting diodes with different wavelengths. The current required to emit light from each of the near-infrared light-emitting diodes is different. Also, even if the near-infrared light-emitting diodes are driven to emit light with the same current, the light output differs due to individual differences in the near-infrared light-emitting diodes. Therefore, the optical signals of each wavelength received by the light-receiving unit 112 also differ, and the signal levels of the analog signals output from the light-receiving amplifier 114 also differ.

[0062] Therefore, in order to calibrate the signal levels output from the light receiving amplifier 114 when each of the near-infrared light emitting diodes emits light at a constant current so that the output signal levels are the same, a coefficient for calibration is stored in advance in the ROM 117. Then, when calculating the hemoglobin absorbance from the signal levels, it is possible to make the absorbances obtained from the absorption coefficients of hemoglobin the same based on the light emitted from the near-infrared light emitting diodes at each wavelength.

[0063] In this way, even if there is an imbalance or variation in the sensitivity between the light emitting unit 111 and the light receiving unit 112 used in the probe 110, such an imbalance or variation in the sensitivity between the light emitting unit 111 and the light receiving unit 112 is calibrated, so that changes in hemoglobin can be accurately measured and the oxygen saturation of the target tissue can be accurately measured.

[0064] Mass-produced devices such as near-infrared light emitting diodes or photodiodes are used for the light emitting unit 111 and the light receiving unit 112 used in the probe 110. However, the characteristics of such devices, for example, the light emission output and the light reception sensitivity, are not exactly the same, and imbalances or variations may occur.

[0065] Therefore, by storing phantom-based calibration data in the ROM 117 in advance as reference values for the transmitted light measured in advance using a phantom capable of obtaining the same absorption characteristics as the living body described later, even if there is an imbalance or variation in the sensitivity between the light emitting unit 111 and the light receiving unit 112 used in the probe 110, the imbalance or variation in the sensitivity between the light emitting unit 111 and the light receiving unit 112 can be calibrated, changes in hemoglobin can be accurately measured, and the oxygen saturation of the target tissue can be measured.

[0066] Specifically, voltage data of the ratio of different light wavelengths in the light emitting unit 111 with an oxygen saturation of 50% on the phantom is stored in the ROM 117. Furthermore, data on the amplification factor of the light receiving amplifier 114 can also be stored.

[0067] Furthermore, the ROM 117 can also store distance information between the light-emitting unit 111 and the light-receiving unit 112, and voltage information for applying an appropriate amount of light to the distance between the light-emitting unit 111 and the light-receiving unit 112. The light-emitting unit 111 can emit light to the living body based on the voltage information.

[0068] The UART (Universal Asynchronous Receiver-Transmitter) 118 is configured to transmit and receive a signal obtained by the probe 110 for transmission to the apparatus main body 120 and a signal for operating the probe 110, and is detachably and replaceably connected to the apparatus main body 120 by a communication cable.

[0069] As described above, in the probe 110, the distance between the light-emitting unit 111 and the light-receiving unit 112 varies according to the depth at which the target tissue for obtaining information exists, and an arbitrarily selectable probe 110 can be selected and used according to the position of the target tissue to be measured. At the time of measurement, the selected probe 110 is set in the apparatus main body 120 and measurement is performed.

[0070] In this way, since the probe 110 used in contact with the living body is made replaceable, only the probe 110 that comes into contact with the living body can be disposable, and health and safety can be improved.

[0071] The apparatus main body 120 is configured such that the probe 110 selected according to the depth of the measurement target tissue is attached, the probe 110 is operated by sending a signal to the probe 110, and the digital signal obtained from the probe 110 is relayed and transmitted, and includes a UART, an MPU 122, a photocoupler 123, a UART 124, a USB interface 125, and a DC / DC converter (direct current converter) from a USB (Universal Serial Bus).

[0072] UART121 is configured to transmit and receive signals obtained from the probe 110 to the apparatus main body 120, and signals for operating the probe 110, and is detachably and replaceably connected to the probe 110 via a communication cable.

[0073] The MPU122 is a microprocessor configured to control each connected device, and is connected to the UART121 and the photocoupler 123. The photocoupler 123 is configured to once convert an electrical signal into an optical signal there, and then convert it back into an electrical signal to transmit the signal under electrical insulation, and is connected to the MPU122 and the UART124 from the USB. In this way, the probe 110 and the terminal device 130 that come into contact with the living body are insulated so as to satisfy the conditions for use as medical devices.

[0074] The UART124 from the USB is a conversion module for converting the signal sent from the photocoupler 123 into a form adapted to the USB interface 125, and is connected to the photocoupler 123 and the USB interface 125.

[0075] The USB interface 125 is a connector for connecting the apparatus main body 120 to the terminal device 130 via a communication cable such as a USB cable. Therefore, the apparatus main body 120 is connected to the terminal device 130 via a USB cable.

[0076] The DC / DC converter 126 is configured to provide a power supply for supplying power from the terminal device 130 connected via a USB cable to the probe 110, and is connected to the USB interface 125 and the UART121.

[0077] The terminal device 130 is configured to perform an arithmetic operation of calculating the oxygen saturation of the target tissue measured by the probe 110 from the information of the target tissue obtained via the apparatus main body 120, and store the result. The terminal device 130 includes a USB interface 131 and a control unit 132.

[0078] The USB interface 131 is a connector configured to connect the terminal device 130 to the apparatus main body 120 via a communication cable such as a USB cable, and is connected to the apparatus main body 120 and the control unit 132. In this way, the terminal device 130 is connected to the apparatus main body 120 via a USB cable.

[0079] The control unit 132 is configured to control the operation of the probe 110 connected via the apparatus main body 120, and is connected to the USB interface 131 and the display 140.

[0080] Furthermore, the control unit 132 can receive, calculate the information measured by the probe 110 via the apparatus main body 120, and output the calculated information to the connected display 140. Specifically, the control unit 132 includes a calculation unit 133, a pulse increase unit 134, a cycle calculation execution unit 135, an ambient light exclusion unit 136, and an information storage unit 137.

[0081] The calculation unit 133 is mainly configured to calculate the oxygen saturation based on Lambert-Beer's law. The calculation unit 133 is also configured to calibrate information based on the calibration data stored in the ROM 117 of the probe 110.

[0082] Furthermore, the calculation unit 133 can also calculate relative values such as the amount of hemoglobin (HbI) and the amount of oxygen metabolism in the target tissue based on the information obtained for measuring rSO2 or SpO2. As a specific calculation method for the amount of oxygen metabolism in the target tissue, it can be calculated by the following formula 1.

[0083] [Formula 1] Oxygen metabolism amount (CMRO2) = HbI × (SpO2 - rSO2)

[0084] The pulse increase unit 134 is configured to increase the pulse rate for the light emitting unit 111 of the probe 110 connected via the apparatus main body 120 based on the instruction information input by an input means (not shown).

[0085] In the oxygen saturation measuring device 100, the light emitting unit 111 emits light to a living body with a pulse capable of measuring rSO2 when measuring the oxygen saturation in a target tissue (hereinafter referred to as the rSO2 mode). Specifically, in the rSO2 mode, the light emitting unit 111 emits light to the living body at a pulse rate of 10 or less per second. Therefore, since light with a low pulse rate is emitted to the living body, heat accumulation does not occur, and rSO2 can be measured without worrying about low-temperature burns.

[0086] Furthermore, the light receiving unit 112 can obtain provisional information by adjusting the intensity of the light emitted from the light emitting unit 111 to an intensity such that the change can be detected by the light receiving unit 112. Therefore, the light emission time from the light emitting unit 111 can be shortened to about 0.1 milliseconds, and the obtained information can be sample-held and the previous data can be held until the next pulse, thereby facilitating data processing.

[0087] In the pulse increase unit 134, the pulse rate in the above-described rSO2 mode is temporarily increased, and the light emitting unit 111 emits light to the living body with a pulse capable of measuring SpO2 in the same manner as a pulse oximeter (hereinafter referred to as the SpO2 mode). Specifically, in the SpO2 mode, the light emitting unit 111 emits light to the living body at a pulse rate of 30 or more per second.

[0088] By limiting the emission time in the SpO2 mode to about 1 minute at maximum, heat accumulation due to near-infrared light can be prevented. Since heat accumulation is reduced, SpO2 can be measured without worrying about low-temperature burns. Thus, the oxygen saturation measurement system 100 can perform measurement using only one probe 110 attached to the living body while switching between and measuring SpO2 and rSO2.

[0089] The periodic operation execution unit 135 is configured to periodically increase the pulse rate by the pulse increase unit 134. For example, the periodic operation execution unit 135 operates the pulse increase unit 134 at a predetermined interval, for example, every 10 minutes. Therefore, the light emitting unit 111 can be periodically used for sampling pulses in the SpO2 mode, so that it becomes possible to measure SpO2. Note that the execution interval of the sampling operation by the periodic operation execution unit 135 is preferably limited to at least about 5 minutes because of concern about heat accumulation in the tissue due to near-infrared light.

[0090] Also, although not shown, in the control unit 132, an rSO2 monitoring unit for monitoring the state of rSO2 in the rSO2 mode is also provided, and when rSO2 decreases, the rSO2 monitoring unit may switch the pulse increase unit 134 to the SpO2 mode.

[0091] In this way, when rSO2 decreases, the operation mode automatically switches to the SpO2 mode, and if no pulse wave is measured, cardiac arrest is presumed. Therefore, it is also possible to generate an alarm (for example, an audible alarm or a visual alarm) from a warning device such as a light or a speaker. In another embodiment, the alarm can be in the form of a message or notification provided to the user.

[0092] The ambient light exclusion unit 136 is configured to exclude intense ambient light. Conventionally, in measurements using light such as near-infrared light, strong ambient light enters and the light receiving unit 112 cannot accurately detect the light. Therefore, measurements are mainly performed in operating rooms, ICUs, hospital rooms, etc. inside the hospital, and measurements outdoors are not particularly performed.

[0093] Furthermore, although the measurement is often carried out indoors, the actual measurement is not performed in a completely dark situation. The light receiving unit 112 of the probe 110 that receives light outputs the light as a signal as long as the light is within the sensitivity region regardless of the wavelength. That is, when trying to obtain only the necessary signals applied from the light emitting unit 111, ambient light passing through the living body is also detected by the light receiving unit 112.

[0094] Then, the ambient light exclusion unit 136 first utilizes the information acquired by the light receiving unit 112 during the lightless state when the light emitting unit 111 does not emit light among the pulses emitted from the light emitting unit 111. Specifically, in the rSO2 mode, the light emitting unit 111 provides four types of light states, namely the lightless state or the light emission states of 770 nm, 805 nm, and 870 nm. The light receiving unit 112 receives such four types of light and stores signals in the information storage unit 137 with a moving average of 1 to 5 seconds, which is used for the calculation in the calculation unit 133.

[0095] In the lightless state where the light emitting unit 111 does not emit light, the light received by the light receiving unit 112 depends on the measurement situation. When measuring in a bright place such as outdoors, bright ambient light is received by the light receiving unit 112 through the living body. Also, when measuring in a dark room indoors, a small amount of light in the dark room is received by the light receiving unit 112 through the living body. These are called ambient light signals.

[0096] Since a signal already caused by ambient light is incident on the light receiving unit 112, when the light emitting unit 111 emits light, the light receiving unit 112 detects the increased ambient light due to the light emission from the light emitting unit 111.

[0097] That is, the necessary light that the light receiving unit 112 should measure is the difference between the light detected by the light receiving unit 112 and the ambient light, and the necessary optical signal that the light receiving unit 112 should measure can be obtained by subtracting the ambient light signal from the light receiving signal in the light receiving unit 112.

[0098] In the ambient light exclusion unit 136, such processing enables the acquisition of an optical signal excluding ambient light. Further, during measurement, the probe 110 is set on the epidermis of the target tissue, and the light receiving unit 112 is shielded from ambient light. Then, an ambient light monitoring unit for monitoring external signals is provided. When the external signal monitored by the ambient light monitoring unit is higher than the level of normal ambient light, it is determined that the probe 110, particularly the light receiving unit 112, has fallen off the epidermis, and it is also possible to generate an alarm (e.g., an audible alarm or a visual alarm) by a warning device such as a light or a speaker. In another embodiment, the alarm can be in the form of a message or notification provided to the user.

[0099] The information storage unit 137 can store the calculation results by the calculation unit 133, can also store the ambient light signals used by the ambient light exclusion unit 136, and is configured to store various information.

[0100] Although it has been described that the apparatus main body 120 and the terminal device 130 are connected by a USB cable via the USB interface 125 and the USB interface 131, the USB interface 125 and the USB interface 131 may also be connected by a wireless communication device capable of communication without using a wired cable such as a communication cable, for example, a transceiver, a transmitter, a receiver, an antenna, etc.

[0101] In this way, the connection parts between devices via the wired communication cable can be reduced, so it is possible to reduce accidents such as those of monitors caused by the hands or feet getting caught during the movement of the patient or during treatment operations.

[0102] Furthermore, in FIGS. 1A and 1B, a double type configuration in which the light emitting unit 111 and the light receiving unit 112 are provided in a pair on the left and right with respect to the probe 110 is shown, but their numbers and positions can be arbitrarily selected and changed.

[0103] For example, a single type configuration in which a light emitting unit 111 is provided on one side with respect to the center of the probe 110 and a light receiving unit 112 is provided on the other side may be used. In the case of the single type configuration, the single type probe 110 is attached to other desired different positions of the living body.

[0104] In the probe 110, usually, since channels each including a set of a plurality of light emitting units 111 and light receiving units 112 are used simultaneously (generally, two channels on the left and right on the forehead), when the plurality of light emitting units 111 and light receiving units 112 operate simultaneously, signals interfere with each other and it becomes impossible to distinguish the signal derivation sources.

[0105] Therefore, it is preferable to control so that the light emitting unit 111 and the light receiving unit 112 of the probe 110 operate independently without interfering with each other based on the clock pulse from the MPU 116 as a reference. Accordingly, the number of communication cables connected to the probe 110 can be reduced as compared with the case of connecting using analog signals.

[0106] Subsequently, a method for measuring oxygen saturation using the oxygen saturation measurement system 100 will be described. First, a probe 110 corresponding to the depth of the tissue to be measured is selected, connected to the apparatus main body 120, and the probe 110 is set on the epidermis of the tissue to be measured.

[0107] Next, the number of channels to be measured and the measurement conditions are specified from the menu screen using the terminal device 130 and the display 140, and the measurement start button is turned on. The apparatus main body 120 reads information from the ROM 117 in the connected probe 110.

[0108] The control pulse is output from the apparatus main body 120 to the probe 110 based on the information acquired from the ROM 117, and the light emitting unit 111 emits light of an amount corresponding to the control pulse in the probe 110 and applies light to the living body.

[0109] When the light applied to the living body passes through the capillary bed in the living body, it is absorbed by oxyhemoglobin and deoxyhemoglobin, and is converted into an analog electrical signal by the light receiving unit 112 as a signal showing different absorptions for each wavelength.

[0110] The converted analog signal is converted into a digital signal by the A / D converter 115, output from the probe 110, and sent to the terminal device 130 via the apparatus main body 120.

[0111] In the terminal device 130, the oxygen saturation of the target tissue is calculated by the control unit 132, and the processed calculation result is displayed on the display 140 and stored in the terminal device 130 at the same time. Furthermore, graphic information such as a trend graph can also be displayed on the display 140. Usually, rSO2 is measured in the rSO2 mode, and SpO2 is measured optionally or periodically.

[0112] FIG. 2 is a block diagram showing an example of information stored in a ROM (read only memory; sometimes also called an information storage device). As shown in FIG. 2, the ROM 117 stores distance information 117A between the light emitting unit 111 and the light receiving unit 112, voltage information 117B of the ratio of different light wavelengths of the light emitting unit 111 when the oxygen saturation on the phantom is 50%, information 117C of the drive voltage of the light emitting unit 111 and the amplification factor of the light receiving amplifier 114, and calibration information 117D of the light emitting unit 111 and the light receiving unit 112. Further, as the distance information 117A between the light emitting unit 111 and the light receiving unit 112, distance information between the light emitting unit 111 and the light receiving unit 112 set according to the depth of the measurement target tissue is stored.

[0113] As the voltage information 117B of the ratio of different light wavelengths in the light emitting unit 111 with an oxygen saturation of 50% on the phantom for calibrating the probe 110, the voltage information of the ratio of different light wavelengths in the light emitting unit 111 with an oxygen saturation of 50% on the phantom is stored as a reference.

[0114] (Calibration with a Phantom) Since the devices used for the light emitting unit 111 and the light receiving unit 112 are mass-produced, for example, their characteristics such as light emission output and light reception sensitivity are not exactly the same as each other, and individually give imbalance or scattering. In order to use such devices for the probe 110, calibration of the characteristics is necessary. Otherwise, accurate measurement values cannot be obtained. Therefore, in the oxygen saturation measurement system according to the present invention, calibration is performed using a phantom.

[0115] FIG. 3 is a graph showing the result of measuring the absorption coefficient of a resin plate. In the present invention, calibration is applied using a phantom, but there is no resin material having equal absorbance for the two wavelengths used as described above. Therefore, a material having substantially equal absorption coefficients between the two wavelengths of light as shown in the results of FIG. 3 is selected and used as a reference for calibration.

[0116] As an example of the selected resin plate, a vinyl chloride plate having a gray appearance and a thickness of 0.5 mm was used. FIG. 3 is a graph showing the result of measuring the absorbance of the gray resin plate using an absorptiometer.

[0117] The absorption coefficient ε of the gray vinyl chloride resin plate is as shown in Table 1 below.

[0118] [Table 1]

[0119] When the amount of oxyhemoglobin in which hemoglobin and oxygen are bound is equal to the amount of deoxyhemoglobin from which oxygen has detached from oxyhemoglobin, the oxygen saturation is 50%. When the ratio (R / IR ratio) of the light absorption amounts of the two wavelengths of light on the phantom is 1.0, the method of calibrating the oxygen saturation to 50% is performed as follows.

[0120] Regarding the light absorption coefficient ε at each wavelength, the values shown in Table 2 below are used.

[0121]

Table 2

[0122] When the absorbance is K, the molar absorption coefficient ε is expressed as ε = 0.434K and is shown as in Table 3 below.

[0123]

Table 3

[0124] According to Lambert-Beer's law, K = εCd, and the absorbance K at wavelength λ is expressed by the following Equation 2.

[0125] [Equation 2] Kλ = (rSO2 × KHbO2 + (1 - rSO2) × KHb)cd

[0126] The absorbance K for each wavelength (770 nm, 805 nm, 870 nm) used in the oxygen saturation measurement system 100 of the present invention is obtained by the following equations starting from Equations 3A - 3C.

[0127] [Equations 3A - 3C] R = K770 = (rSO2 × 0.368 + (1 - rSO2) × 0.806)cd (3A) IR = K870 = (rSO2 × 0.576 + (1 - rSO2) × 0.414)cd (3B) R / IR = (0.806 - 0.438 × rSO2) / (0.414 + 0.162 × rSO2) (3C)

[0128] When R / IR = A, A is expressed by the following Equations 4A - 4B.

[0129] [Equations 4A - 4B] A = (0.806 - 0.438·rSO2) / (0.414 + 0.162·rSO2) (4A) A(0.414 + 0.162·rSO2) = (0.806 - 0.438·rSO2) (4B)

[0130] From this, when calculating rSO2, it is expressed by the following Equation 5.

[0131] [Equation 5] rSO2 = (0.806 - 0.414A) / (0.438 + 0.162A)

[0132] When rSO2 changes from 0% to 100%, the theoretical value of A = R / IR is expressed by the following Equations 6A - 6B.

[0133] [Equations 6A - 6B] · 0% rSO2 (0.806 - 0.414 × 1.186A) = 0 A = 1.64 (6A) · 100% rSO2 (0.438 + 0.162 × 1.186A) = (0.806 - 0.414 × 1.186A) A = 0.539 (6B)

[0134] When calculating the absorbance K at the wavelength where rSO2 = 50%, that is, rSO2 = 0.5, K is expressed by the following Equations 7A - 7C.

[0135] [Equations 7A - 7C] Kλ = (rSO2 × KHbO2 + (1 - rSO2) × KHb)cd (7A) K770 = (0.5 × 0.368 + 0.5 × 0.806)cd = 0.587cd (7B) K870 = (0.5 × 0.576 + 0.5 × 0.414)cd = 0.495cd (7C)

[0136] Next, R / IR = A = 1.186. At the theoretical value, the absorbances at two wavelengths when rSO2 = 50% are as described above. The absorbance at R = K770 is 0.587cd, the absorbance at IR = K870 is 0.495cd, and the absorbance of R is larger.

[0137] Next, the measured voltage at a wavelength of 770 is corrected by multiplying by the absorbance ratio of 1.186. Then, the absorbance at K770 becomes 0.495 cd, the absorbance at K870 becomes 0.495 cd, and the R / IR ratio becomes 1:1. With this correction, the measured value by the oxygen saturation measurement system 100 of the present invention becomes rSO2 = 50% at R / IR = 1, which is consistent with the theoretical value.

[0138] Since R / IR = A is 1.175 / 0.968 = 1.214, the theoretical oxygen saturation of the resin plate is 1.186:1.214 when compared with the absorbance ratio of oxyhemoglobin and deoxyhemoglobin, which is substantially equal to 97.7%. The value obtained by correcting 1.186 based on the phantom value with 50% based on the resin plate has an accuracy of 97.7%.

[0139] When corrections are also made for 0% and 100%, each absorbance ratio A = R / IR is as described below, and the calculation formula for rSO2 (theoretical value) is represented by the following mathematical formula 8.

[0140] [Mathematical formula 8] rSO2=(0.806 - 0.414A) / (0.438 + 0.162A)

[0141] When multiplying A by 1.186 for correction and rSO2 changes from 0% to 100%, the theoretical values of A = R / IR are represented by the following mathematical formulas 9A - 9B.

[0142] [Mathematical formulas 9A - 9B] ·0% rSO2 (0.806 - 0.414×1.186A)=0 A = 1.64(9A) ·100% rSO2 (0.438 + 0.162×1.186A) =(0.806 - 0.414×1.186A) A = 0.539(9B)

[0143] The calculation formulas for the calibration curve based on the theoretical values corrected as described above are represented by the following mathematical formulas 10A - 10B.

[0144] [Formula 10A-10B] When A < 1, rSO2 = 100×(1.539 - A) / 1.08; 100 - 50%(10A). When A > 1, rSO2 = 100×(1.64 - A) / 1.28; 50 - 0%(10B)

[0145] When the wavelengths of the light used are different, since the absorption coefficients ε for oxyhemoglobin and deoxyhemoglobin at each wavelength are known, the value is applied to ε = 0.434K and recalculated.

[0146] As described above, since the phantom having the same light absorption and scattering characteristics as the living body can be applied to different wavelengths, when used at 805 nm, the absorbance by the phantom can be used as a measurement standard for the amount of hemoglobin.

[0147] As a phantom providing a reference for oxygen saturation, resin plates with absorption coefficients (μa = 0.15 / cm) and scattering coefficients ((μs = 10.6 / cm) substantially equal to those of a living body or an adult skull are used, and by stacking a plurality of them, a structure with little wavelength dependence, for example, a structure sealed against ambient light, is formed.

[0148] Thus, in the wavelength range of 770 nm - 870 nm of the near-infrared light emitted from the light-emitting unit 111, both the scattering coefficient and the diffusion coefficient can be regarded as constant. By stacking such resins to a thickness of about 30 mm and combining them as a resin plate simulating a state where both oxyhemoglobin and deoxyhemoglobin are present in equal amounts respectively, a diffusion and scattering state substantially the same as that of an adult skull can be reproduced and used as a measurement standard for oxygen saturation and hemoglobin index.

[0149] "Absorption is equal for two types of light wavelengths" means "corresponding to an oxygen saturation of 50%". By storing the measured values of R and IR required for calibration on the phantom in the ROM 117 and using them as a reference when the oxygen saturation is 50%, it is possible to calibrate the probe 110.

[0150] (Method for preparing calibration data of probe 110) To ensure the accuracy of the probe 110 manufactured so far in calibration verification, there is a method of preparing a reference phantom in a blood bath, but this requires large-scale equipment and systems.

[0151] Therefore, the present invention provides a method for calibrating the probe 110 by arbitrarily adjusting the blood oxygen saturation based on the data R and IR of the absorption amount of blood at each wavelength obtained using the probe 110 actually used, and a method for correcting the imbalance, variation, and error occurring in the device used for the probe 110.

[0152] First, a blood gas analyzer capable of measuring the oxygen saturation of blood, a cuvette for injecting a blood sample to be measured (the thickness of the blood layer is 1 mm - 2 mm), a reducing agent for reducing the oxygen saturation of the sample blood (sodium hydrosulfite sodium dithionite Na2S2O4), a container for containing the sample blood, and a syringe for mixing air into the blood are provided.

[0153] In order to approximate the concentration of the blood filled in the cuvette to the maximum concentration in the tissue (cerebral cortex) existing in the capillaries of the living body when the concentration of human whole blood is actually measured at 15 g / dL, the blood is diluted with physiological saline to about 1 / 3 - 1 / 5 and used.

[0154] (Method for measuring calibration value of oxygen saturation) Fresh blood of a pig is collected, the blood to be measured is filled in a cuvette with a thickness of 1 mm, and the oxygen saturation is measured in an environment where environmental light is blocked. The procedure is as follows.

[0155] (Step S1) Dilute the blood 3 - 5 times with physiological saline to approach the concentration in the capillary bed. (Step S2) Add about 2% by weight of the reducing agent to reduce the oxygen saturation as much as possible. (Step S3) Aspirate the blood with adjusted oxygen saturation using a syringe, and record the oxygen saturation with a blood gas measuring device. (Step S4) Fill the cuvette with blood, measure the oxygen saturation with the probe 110, and record the voltage data of R and IR. (Step S5) Increase the oxygen saturation by stirring the blood and bringing it into contact with air. (Step S6) Measure and record the value of the oxygen saturation with a blood gas measuring device. (Step S7) Fill the cuvette with blood, measure rSO2 with the probe 110, and record the voltage measurement values of R and IR.

[0156] The processes from Step S3 to Step S7 are repeated from a low value of oxygen saturation to as high an oxygen saturation as possible. As described above, a reference value regarding transmitted light is measured in advance using a phantom that can obtain the same absorption characteristics as the living body, or a reference value regarding transmitted light is measured in advance using blood adjusted to an optional oxygen saturation, and this can be stored in the ROM 117 as a reference value.

[0157] Regarding the information 117C of the drive voltage in the light emitting unit 111 and the amplification factor in the light receiving amplifier 114, voltage information for applying an appropriate amount of light and amplification information for amplifying the signal received by the light receiving unit 112 to a necessary signal level with respect to the distance between the light emitting unit 111 and the light receiving unit 112 are stored.

[0158] (Calculation method of the amount of light with respect to the distance between the light emitting unit 111 and the light receiving unit 112) When the amount of oxyhemoglobin in which hemoglobin is combined with oxygen is equal to the amount of deoxyhemoglobin from which oxygen has detached from hemoglobin, the oxygen saturation is 50%.

[0159] The calculation formula for oxygen saturation is generally expressed by the following formula 11.

[0160] [Formula 11] Oxygen saturation = (amount of oxyhemoglobin) / (amount of oxyhemoglobin + amount of deoxyhemoglobin)

[0161] The absorption rate of light with respect to hemoglobin varies depending on the wavelength of the light emitted from the light emitting unit 111. Light with a wavelength of 805 nm exhibits equal absorption coefficients for oxyhemoglobin and deoxyhemoglobin.

[0162] Assuming the concentration is C and the absorption coefficient is ε of the medium according to Lambert-Beer's law, the absorbance K as the amount of absorbed light is represented by the following mathematical formulas 12A - 12B.

[0163] [Mathematical formulas 12A - 12B] K = εCd (12A) C = K / (εd) (12B)

[0164] Furthermore, the absorbance K is represented by the following mathematical formula 13 in terms of the incident light, which is the light before entering the medium, and the transmitted light, which is the light after passing through the medium with a thickness d:

[0165] [Mathematical formula 13] K = Log (incident light / transmitted light)

[0166] Thus, if the absorbance K at two wavelengths of light can be measured, the medium concentration C can be calculated.

[0167] The probe 110 can perform necessary calibration using a reference phantom with equal concentrations (absorbances) of oxyhemoglobin and deoxyhemoglobin. Since the absorbance K is represented as K = εCd as in Mathematical formula 2, when the amount of oxyhemoglobin and the amount of deoxyhemoglobin are equal, the concentration C of the medium is 50%.

[0168] When the concentration C of the medium at each wavelength is obtained, when the concentration of oxyhemoglobin and the concentration of deoxyhemoglobin are equal, rSO2 becomes 50%. The absorption coefficients ε (m·mol / cm) of oxyhemoglobin and deoxyhemoglobin at each light wavelength are as shown in the following Table 4.

[0169] [Table 4]

[0170] Regarding the absorbance K at two wavelengths of light, when the wavelength of 770 nm is D7 and the wavelength of 870 nm is S8, and the concentration C of the medium is equal for oxyhemoglobin and deoxyhemoglobin, the values of D7 and S8 result in rSO2 = 50% and are represented by the following Equation 14. The values of D7 and S8 are determined based on the voltage during measurement.

[0171] [Equation 14] C(deoxyhemoglobin) = (D7 / 0.35) + S8 / 0.18 = C(oxyhemoglobin) = (D7 / 0.16) + S8 / 0.25

[0172] If the ratio of the light absorption amounts (R / IR ratio) at two wavelengths of light measured by D7 and S8 is 1.0, the oxygen saturation is 50%, and the value is stored in ROM117.

[0173] In a pulse oximeter, since it is known that the ratio of the light absorption amounts (R / IR ratio) at two wavelengths of light is correlated with the oxygen saturation, if a calibration curve is prepared based on the ratio of the light absorption amounts (R / IR ratio) at two wavelengths of light obtained by the probe 110 during measurement and the oxygen saturation SpO2 obtained from the blood whose oxygen saturation has been adjusted by a blood gas analyzer, the oxygen saturation can be accurately calculated based on the actually measured R / IR ratio.

[0174] (Calculation method of hemoglobin amount) Referring to the change in the amount of hemoglobin, the level of the received signal of the light receiving unit 112 for light with a wavelength of 805 nm is inversely proportional to the change in the amount of hemoglobin. Since the greater the amount of hemoglobin, the greater the light absorption, the signal received by the light receiving unit 112 becomes weaker and the output voltage decreases.

[0175] Then, based on the signal level at the start of measurement as a reference, it is considered that as the signal increases thereafter, the absorption amount of hemoglobin decreases. Using the value of the signal at the start of measurement as the denominator and the value of the current signal as the numerator, the current hemoglobin amount can be calculated based on 1.0 at the start of measurement.

[0176] Normally, the sensor is set on the subject, and since the value of the optical signal at a wavelength of 805 nm due to absorption by hemoglobin directly below the sensor is converted into a measured value, the voltage at the start of measurement is defined as the reference value 1.0.

[0177] The degree to which the light at a wavelength of 805 nm is absorbed by hemoglobin is calculated based on the Lambert-Beer law, based on the absorbance K = Log(incident light / transmitted light). Since the intensity of the light actually incident on the living body cannot be measured on the spot, it is calculated assuming that it is about 1000 times the signal light received by the light receiving unit 112.

[0178] (Calculation method of oxygen saturation) Oxygen saturation is the ratio representing the proportion of oxyhemoglobin based on the whole hemoglobin. When the amount of oxyhemoglobin and the amount of deoxyhemoglobin are in a ratio of 1:1, the oxygen saturation is 50%.

[0179] According to the Lambert-Beer law, based on the voltage signals of R = 770 nm and IR = 870 nm indicating the absorbance of each light at two wavelengths of light, the absorbance can be obtained. Therefore, the amount of oxyhemoglobin and the amount of deoxyhemoglobin can be calculated together with a linear equation of two variables, and further, the oxygen saturation can be calculated based on this. Generally, the ratio of the absorbance amounts between the two wavelengths of light (R / IR ratio) is said to be correlated with the oxygen saturation, which constitutes the basis for the calculation in a pulse oximeter.

[0180] (Measured value of rSO2) An example of a calibration curve determined based on the measurement values obtained through the processes from step S1 to step S7 is shown in Table 5 below. In the relational expression for obtaining the oxygen saturation based on the measured values of the absorbance ratio (R / IR ratio) of the wavelengths of two types of light, it is assumed that the wavelengths of D7 = 770 nm and S8 = 870 nm are used.

[0181]

Table 5

[0182] The distance to the light emitting unit 111 and the distance to the light receiving unit 112 are generally selected as shown in Table 6 below based on the depth of the tissue to be measured. Since the position where capillaries exist varies depending on the depth and site of the tissue to be measured, it is necessary to individually determine the optimal calculation formula and constants in order to obtain accurate values.

[0183]

Table 6

[0184] When measuring the blood oxygen saturation in vivo using near-infrared light, it is required to measure while selecting the part where the target tissue containing blood in the body exists. For example, when the tissue to be measured is the cerebral cortex of an adult, since the cerebral cortex exists at a depth of about 17 mm - 25 mm from the epidermis through the skull, about 70 - 80% of the distance between the light emitting unit 111 and the light receiving unit 112 of the probe 110 becomes the maximum measurable depth. Therefore, it is necessary that the distance between the light emitting unit 111 and the light receiving unit 112 of the probe 110 is 40 mm - 30 mm.

[0185] Furthermore, when measuring blood flow only in the epidermis, since the capillaries in the dermis and epidermis are located at a depth of about 1.5 mm from the skin surface, a distance of about 2.5 mm - 2.0 mm is required between the light emitting unit 111 and the light receiving unit 112 of the probe 110 in order to obtain information only about the epidermis.

[0186] Furthermore, in order to obtain blood information from target tissues other than the above, such as muscle tissue or the organ itself, an appropriate distance is required between the light-emitting unit 111 and the light-receiving unit 112 of the probe 110 according to the depth of the target tissue from the probe 110 attached to the epidermis, and the light-emitting unit 111 needs to emit an appropriate amount of light according to the distance between the light-emitting unit 111 and the light-receiving unit 112.

[0187] When the distance between the light-emitting unit 111 and the light-receiving unit 112 of the probe 110 is different, in order to improve the accuracy of the oxygen saturation calculation formula, it is necessary to set a correction coefficient obtained from the calculation curve according to the distance between the light-emitting unit 111 and the light-receiving unit 112 of the probe 110.

[0188] When the probe 110 used for measurement is connected to the apparatus main body 120, it is configured such that the calibration information stored in the ROM 117 is read by the terminal device 130. For example, if the distance between the light-emitting unit 111 and the light-receiving unit 112 of the probe 110 is 40 mm, considering the calculation formula in Table 2, the voltage required for the amount of light applied from the light-emitting unit 111 can be set to 1.0 V.

[0189] As the calibration information 117D for the light-emitting unit 111 and the light-receiving unit 112, coefficient information for calibration is stored so that the signal levels output from the light-receiving amplifier 114 are the same when each near-infrared light-emitting diode emits light at a predetermined current.

[0190] As described above, an optimal calculation formula can be set based on the respective calibration information of the probe 110 stored in the ROM 117, and the measurement results can be calculated, displayed, and recorded. Furthermore, since the terminal device acquires optimal information via the apparatus main body 120 and performs measurement with the probe 110, it is possible to realize the oxygen saturation measurement system 100 with high accuracy and reproducibility by simply selecting the probe 110 optimal for the depth of the target tissue to be measured.

[0191] Regarding the optimal light intensity and signal amplification factor for measurement, assuming that it is optimal when the light source is 1, the amplification factor is 200 times when the distance between the light emitting unit 111 and the light receiving unit 112 is 40 mm, the light source is 1 / 2, the amplification factor is 50 times when the distance between the light emitting unit 111 and the light receiving unit 112 is 30 mm, the light source is 1 / 8, the amplification factor is 5 times when the distance between the light emitting unit 111 and the light receiving unit 112 is 20 mm, the light source is 1 / 10, the amplification factor is 1 time when the distance between the light emitting unit 111 and the light receiving unit 112 is 10 mm, the light source is 1 / 20, the amplification factor is 1 time when the distance between the light emitting unit 111 and the light receiving unit 112 is 6 mm, and the light source is 1 / 40, the amplification factor is about 1 time when the distance between the light emitting unit 111 and the light receiving unit 112 is 3 mm.

[0192] Furthermore, according to the present embodiment, distance information between the light emitting unit 111 and the light receiving unit 112 that is positioned corresponding to the depth of the target tissue, and voltage information for applying an amount of light corresponding to the distance between the light emitting unit 111 and the light receiving unit 112 are stored in the ROM 117 of the probe 110. Also, by storing distinguishable identification information for the probe 110 corresponding to the distance between the light emitting unit 111 and the light receiving unit 112, and storing the distance information corresponding to the identification information and the voltage information corresponding to the distance in the terminal device 130, it is also possible to use a configuration that emits a necessary amount of light from the light emitting unit 111 to the living body.

[0193] In the rSO2 mode, by using the moving average value from 1 second to 5 seconds and obtaining the R / IR ratio based on the data for each pulse, considering the correlation between the calculated R / IR ratio, oxygen saturation, and hemoglobin index (HbI), the R / IR ratio is obtained from the data at each wavelength, and the tissue oxygen saturation (rSO2) and hemoglobin index (HbI) can be calculated.

[0194] Furthermore, in the SpO2 mode, instead of using the moving average value as in the rSO2 mode, the changes in the signal values are continuously connected, and the fluctuating trajectory is recognized as a pulse wave. Then, the number of pulses is measured by counting the cycles in which the measured value of each wavelength changes from an increase to a decrease or from a decrease to an increase.

[0195] Regarding the measurement of arterial oxygen saturation in the SpO2 mode (SpO2), the constant part with no change is excluded from the calculation target as information on venous blood, and the arterial oxygen saturation (SpO2) is measured using the R / IR ratio only for the changing part.

[0196] Figure 4 is a graph showing the correlation between the absorbance ratio (R / IR ratio) and the oxygen saturation. Figure 4 is a reference graph of a graph showing the correlation between the absorbance ratio (R / IR ratio) of a gray vinyl chloride resin plate and the oxygen saturation. When the amount of oxyhemoglobin in which hemoglobin is combined with oxygen and the amount of deoxyhemoglobin from which oxygen has detached from oxyhemoglobin are the same, the oxygen saturation is 50%. In the present invention, it is calibrated so that the oxygen saturation becomes 50% when the absorbance ratio (R / IR ratio) at two wavelengths of light on the phantom is 1.0.

[0197] Figure 5 is a graph showing the changes in the absorption coefficients of oxyhemoglobin, deoxyhemoglobin, and carboxyhemoglobin. The absorbance by hemoglobin varies depending on the wavelength of the applied light, and the light at 805 nm is the wavelength at which oxyhemoglobin and deoxyhemoglobin show the same isosbestic point.

Claims

1. An oxygen saturation measuring device that measures the oxygen saturation of a living body by measuring near-infrared light radiated from a light-emitting circuit toward the living body and received by a light-receiving circuit, comprising: an information storage device configured to store distance information between the light-emitting circuit and the light-receiving circuit; a light-emitting drive circuit configured to emit light from the light-emitting circuit with a light amount corresponding to the distance information; a controller configured to provide a first control pulse to the light-emitting drive circuit so that the light-emitting circuit emits an optical pulse configured to measure the oxygen saturation of tissue; the controller further configured to provide a second control pulse to the light-emitting drive circuit so that the light-emitting circuit emits an optical pulse configured to measure arterial blood oxygen saturation; An oxygen saturation measuring device comprising the above.

2. The oxygen saturation measuring device according to claim 1, wherein the light-receiving circuit is positioned corresponding to the depth of the measurement target of the oxygen saturation of the tissue.

3. The oxygen saturation measuring device according to claim 1, wherein the controller is configured to provide the second control pulse for a predetermined time.

4. The controller is configured to calculate an ambient light signal corresponding to ambient light near the light-receiving circuit, and the ambient light signal is based on a difference between a first optical signal measured by the light-receiving circuit due to light emitted by the light-emitting circuit and a second optical signal measured by the light-receiving circuit due to the absence of light from the light-emitting circuit. The oxygen saturation measuring device according to claim 1.

5. The information storage device stores an f reference value regarding transmitted light measured in advance using a phantom configured to obtain the same absorption characteristics as the living body, and is configured to execute calculations by comparing with the reference value. The oxygen saturation measuring device according to claim 1.

6. The information storage device stores a reference value regarding transmitted light measured in advance by using blood adjusted to a preselected oxygen saturation, and is configured to execute calculations by comparing with the reference value. The oxygen saturation measuring device according to claim 1.

7. With the first control pulse, the light-emitting circuit emits 10 or fewer optical pulses per second, and with the second control pulse, the light-emitting circuit emits 30 or more optical pulses per second. The oxygen saturation measuring device according to claim 1.

8. The oxygen saturation measuring device according to claim 1, wherein the light receiving circuit acquires one sample for each light pulse from the light emitting circuit and holds the acquired sample until the next light pulse is provided by the light emitting circuit.

9. A probe, comprising: an information storage device configured to store distance information between a light emitting circuit and a light receiving circuit that is located corresponding to the depth of an object to be measured for the oxygen saturation of tissue; a light emission driving circuit configured to emit light in an amount corresponding to the depth of the object from the light emitting circuit; a microprocessor coupled to the light emission driving circuit, the microprocessor being configured to output a control pulse to the light emission driving circuit so as to emit a light pulse configured such that the light emitting circuit measures tissue oxygen saturation; the probe.

10. The probe according to claim 9, wherein the microprocessor is configured to provide a second control pulse to the light emission driving circuit so as to emit a light pulse configured such that the light emitting circuit measures arterial blood oxygen saturation.

11. The probe according to claim 10, wherein the microprocessor provides the second control pulse for a predetermined time period.

12. A method for measuring the oxygen saturation of a living body, comprising: storing, by an information storage device, distance information between a light emitting circuit and a light receiving circuit that is located corresponding to the depth of an object to be measured for the oxygen saturation of tissue; causing the light emission driving circuit to emit light in an amount corresponding to the distance information to the light emitting circuit; providing a first control pulse to the light emitting circuit so as to emit a light pulse configured such that the light emitting circuit measures the oxygen saturation of tissue; providing a second control pulse to the light emitting circuit for a predetermined time so as to output a light pulse configured such that the light emitting circuit measures arterial blood oxygen saturation the method.

13. The method according to claim 12, wherein the light is near-infrared light.

14. Providing the second control pulse to the light emission driving circuit includes providing the second control pulse for a predetermined time period, the method according to claim 12.

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