Oxygen saturation measurement device, oxygen saturation measurement method, and oxygen saturation measurement program

Abstract

The oxygen saturation measuring device specifies a first light projection time at which the first light-emitting element projects red light and a second light projection time at which the second light-emitting element projects infrared light on the basis of a peak time and a valley time in one beat of a third pulse wave signal corresponding to the light intensity of the received light of the reference light. The reference light has an absorption coefficient of oxyhemoglobin and an absorption coefficient of deoxyhemoglobin higher than wavelengths of red light and infrared light, so that the first light-emitting element projects red light at a first light projection time, and the second light-emitting element projects infrared light at a second light projection time. The oxygen saturation of the artery is measured on the basis of a first pulse wave signal output by the light receiving element from the red light projected at the first light projection time and a second pulse wave signal output by the light receiving element from the infrared light projected at the second light projection time.

Description

Technical Field

[0001] The present disclosure relates to an oxygen saturation measurement device, an oxygen saturation measurement method, and an oxygen saturation measurement program. Background Art

[0002] Conventionally, oxygen saturation (S P As an example of a method for measuring blood pressure (22), a measuring method using absorption spectroscopy is known, such as Japanese Patent Publication No. 2008-167868. In Japanese Patent Publication No. 2008-167868, red light and infrared light having different wavelengths are projected onto arterial blood, and transmitted light or reflected light corresponding to each light is received by a light receiving element. It should be noted that, hereinafter, for the sake of convenience of description, light received by a light receiving element, such as transmitted light and reflected light, is collectively referred to as "received light".

[0003] Specifically, based on the maximum and minimum values ​​obtained from the pulse wave signal of the received light, the amplitudes of two or more pulse wave signals are calculated for red light and infrared light respectively. In order to increase the number of acquired data for amplitude calculation, the projection interval and the reception interval of the red light and infrared light used for measurement are usually repeated twice or more at an interval shorter than one pulsation interval of the artery of the measurement object.

[0004] The variable component (AC) and the fixed component (DC) of the pulse wave signal are calculated based on the calculated two or more amplitudes, and the perfusion index (PI value) of each of the red light and the infrared light is calculated based on the calculated variable component and the fixed component. Furthermore, by introducing the ratio of the PI value of the red light to the PI value of the infrared light (i.e., the absorbance ratio) into a predetermined calculation formula for calculating the oxygen saturation, the oxygen saturation as the measured value can be calculated.

[0005] Furthermore, in Japanese Patent Application Laid-Open No. 2008-167868, predetermined pulse wave information such as the number of samples of the pulse wave signal obtained by one pulsation and the number of pulses is obtained based on the pulse wave signal outputted in accordance with the light intensity of the received light. In Japanese Patent Application Laid-Open No. 2008-167868, by setting the interval of the light emission time of the light emitting element based on the obtained pulse wave information, the oxygen saturation can be measured with high accuracy, and the power consumption of the oxygen saturation measuring device can be reduced.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2008-167868 Summary of the invention

[0009] Problems to be solved by the invention

[0010] Here, the perfusion of blood flow is relatively low, that is, the weaker the light intensity of the pulse wave signal of the received light, the lower the SN ratio, so the calculation accuracy of the amplitude of the pulse wave signal becomes low. In this regard, in the case of Japanese Patent Laid-Open No. 2008-167868, only the pulse wave signals of the received light of red light and infrared light are used in the measurement. Therefore, in the case of a low SN ratio of the pulse wave signal of the received light, the accuracy of the pulse wave information obtained from the pulse wave signal is also reduced, or the necessary pulse wave information cannot be obtained. As a result, it is difficult to set the interval of the light emission time based on the pulse wave information.

[0011] The present disclosure has been made in view of the above-mentioned situation, and provides an oxygen saturation measurement device, an oxygen saturation measurement method, and an oxygen saturation measurement program capable of improving measurement accuracy.

[0012] Means for solving problems

[0013] The oxygen saturation measurement device of the first aspect of the present disclosure comprises: a sensor unit having: a first light emitting element that projects red light onto an artery; a second light emitting element that projects infrared light onto an artery; a third light emitting element that projects reference light onto the artery, the reference light having a wavelength at which the absorption coefficient of oxyhemoglobin and the absorption coefficient of deoxyhemoglobin are higher than those of red light and infrared light; and a light receiving element that receives transmitted light or reflected light corresponding to the projected red light, infrared light, and reference light, respectively, as received light, and outputs a first pulse wave signal corresponding to the light intensity of the received red light, a second pulse wave signal corresponding to the light intensity of the received infrared light, and a third pulse wave signal corresponding to the light intensity of the received reference light. number; and a processor, which is electrically connected to the first light emitting element, the second light emitting element and the light receiving element, determines a first light projection time at which the first light emitting element projects red light and a second light projection time at which the second light emitting element projects infrared light based on the peak time and the trough time of the third pulse wave signal in one beat, causes the first light emitting element to project red light at the determined first light projection time, and causes the second light emitting element to project infrared light at the determined second light projection time, calculates oxygen saturation based on a first pulse wave signal obtained based on the light intensity of received light of the red light projected at the first light projection time, and a second pulse wave signal obtained based on the light intensity of received light of the infrared light projected at the second light projection time, thereby determining the oxygen saturation of the artery.

[0014] According to the first aspect, the wavelength of the reference light projected onto the artery is a wavelength at which the absorption coefficient of oxyhemoglobin and the absorption coefficient of deoxyhemoglobin are higher than those of red light and infrared light. Therefore, the SN ratio of the third pulse wave signal corresponding to the reference light is higher than that of the first pulse wave signal corresponding to the red light and the second pulse wave signal corresponding to the infrared light. That is, the SN ratio of the pulse wave signal of the received light depends on the wavelength of the projected light.

[0015] Therefore, by projecting the red light for measurement at the first light projection time determined based on the peak time and the trough time of the third pulse wave signal, the calculation accuracy of the amplitude of the first pulse wave signal of the received light corresponding to the red light is improved. Similarly, by projecting the infrared light for measurement at the second light projection time determined based on the peak time and the trough time, the calculation accuracy of the amplitude of the second pulse wave signal of the received light corresponding to the infrared light is improved. As a result, the measurement accuracy of the oxygen saturation measured based on the first pulse wave signal and the second pulse wave signal is improved.

[0016] In addition, in the second mode, according to the first mode, the processor is configured to calculate the pulsation interval of the predicted pulsation of the third pulse wave signal that is expected to arrive, the predicted peak moment and the predicted trough moment in the predicted pulsation based on the peak moment and the trough moment of the acquired third pulse wave signal, and determine the first light projection moment and the second light projection moment in the predicted pulsation based on the calculated predicted peak moment and the predicted trough moment.

[0017] According to the above configuration, the first light projection timing and the second light projection timing can be determined with improved accuracy.

[0018] In addition, in the third mode, according to the second mode, the processor is configured to respectively determine the first light projection time and the second light projection time during a first maximum side light projection period after a moment of 2 / 3 of the pulsation interval of the predicted pulsation from the peak moment of the pulsation immediately before the predicted pulsation and ending at the predicted peak moment, and a first minimum side light projection period after a predicted trough moment of the predicted pulsation and ending at a moment of 1 / 3 of the pulsation interval of the predicted pulsation from the predicted trough moment.

[0019] According to the above configuration, the first light projection timing and the second light projection timing can be determined with further improved accuracy.

[0020] In addition, in the fourth mode, according to any one of the first to third modes, the processor is configured to: set a maximum side threshold value of the amplitude based on the maximum amplitude of the third pulse wave signal obtained at the peak moment, set a minimum side threshold value of the amplitude based on the minimum amplitude of the third pulse wave signal obtained at the trough moment, and determine the first light projection time and the second light projection time during the second maximum side light projection period when the amplitude is above the maximum side threshold value and the second minimum side light projection period when the amplitude is below the minimum side threshold value during the pulsation of the third pulse wave signal, respectively.

[0021] According to the above configuration, the first light projection timing and the second light projection timing can be determined with improved accuracy.

[0022] In the fifth aspect, according to the fourth aspect, the maximum side threshold is not less than 2 / 3 of the difference between the maximum amplitude and the minimum amplitude, and the minimum side threshold is not more than 1 / 3 of the difference between the maximum amplitude and the minimum amplitude.

[0023] According to the above configuration, the first light projection timing and the second light projection timing can be determined with further improved accuracy.

[0024] In addition, in the 6th mode, according to any one of the 1st mode to the 5th mode, the processor is configured to calculate a variation coefficient representing the state of the pulsation based on the pulsation interval of the obtained third pulse wave signal, and when the calculated variation coefficient is below a predetermined threshold value, perform the following processing 1; when the variation coefficient exceeds the threshold value, perform the following processing 2.

[0025] (Process 1)

[0026] Based on the peak time and trough time of the acquired third pulse wave signal, the pulsation interval of the predicted pulsation of the third pulse wave signal to be expected, the predicted peak time and the predicted trough time in the predicted pulsation are calculated,

[0027] Based on the calculated predicted peak moment and predicted trough moment, a first light projection moment and a second light projection moment in the predicted pulsation are determined.

[0028] (Process 2)

[0029] Based on the maximum amplitude of the third pulse wave signal obtained at the peak time, a maximum side threshold of the amplitude is set.

[0030] Based on the minimum amplitude of the third pulse wave signal obtained at the trough time, the minimum side threshold of the amplitude is set.

[0031] During the pulsation of the third pulse wave signal, the first light projection timing and the second light projection timing are determined during the second maximum side light projection period when the amplitude is greater than the maximum side threshold and during the second minimum side light projection period when the amplitude is less than the minimum side threshold, respectively.

[0032] According to the above configuration, it is possible to select a suitable oxygen saturation measurement process according to the pulse state of the subject.

[0033] Furthermore, in a seventh aspect, according to the sixth aspect, the threshold value of the coefficient of variation is 0.1 or less.

[0034] According to the above configuration, it is possible to improve the switching accuracy of the oxygen saturation level measurement process.

[0035] In addition, in an eighth aspect, the oxygen saturation level measurement device in any of the first to seventh aspects is a wearable device that can be worn by a person being measured.

[0036] Here, in the case of a measuring device such as a wearable device driven by a relatively small primary battery or secondary battery, it is difficult to increase the light projection power each time because it is necessary to avoid shortening the continuous use time. However, according to the above configuration, by suppressing the calculation load, it is possible to reduce the input power. Therefore, it is possible to realize a wearable device that can achieve a long life.

[0037] The oxygen saturation measuring method of the 9th mode of the present disclosure projects reference light onto an artery, the reference light having an absorption coefficient of oxyhemoglobin and an absorption coefficient of deoxyhemoglobin that are higher than the wavelength of red light and infrared light, receives transmitted light or reflected light corresponding to the projected reference light as received light, obtains a third pulse wave signal corresponding to the light intensity of the received light of the reference light, determines a first light projection time for projecting red light and a second light projection time for projecting infrared light based on the peak moment and the trough moment of the obtained third pulse wave signal in one beat, projects red light at the determined first light projection time, projects infrared light at the determined second light projection time, calculates oxygen saturation based on the first pulse wave signal obtained based on the light intensity of the received light of the transmitted light or reflected light corresponding to the red light projected at the first light projection time, and the second pulse wave signal obtained based on the light intensity of the received light of the transmitted light or reflected light corresponding to the infrared light projected at the second light projection time, thereby measuring the oxygen saturation of the artery.

[0038] According to the ninth aspect, similarly to the first aspect, it is possible to realize an oxygen saturation level measuring method capable of improving measurement accuracy.

[0039] The oxygen saturation measurement program of the 10th mode of the present disclosure causes the processor to perform the following processing: projecting reference light onto the artery, the reference light having an absorption coefficient of oxyhemoglobin and an absorption coefficient of deoxyhemoglobin being higher than a wavelength of red light and infrared light; receiving transmitted light or reflected light corresponding to the projected reference light as received light; obtaining a third pulse wave signal corresponding to the light intensity of the received light of the reference light; determining a first light projection time for projecting red light and a second light projection time for projecting infrared light based on the peak time and the trough time of the obtained third pulse wave signal in one beat; projecting red light at the determined first light projection time; projecting infrared light at the determined second light projection time; and calculating the oxygen saturation based on the first pulse wave signal obtained based on the light intensity of the received light of the transmitted light or reflected light corresponding to the red light projected at the first light projection time and the second pulse wave signal obtained based on the light intensity of the received light of the transmitted light or reflected light corresponding to the infrared light projected at the second light projection time, thereby measuring the oxygen saturation of the artery.

[0040] According to the tenth aspect, similarly to the first aspect, it is possible to realize an oxygen saturation level measurement program capable of improving measurement accuracy.

[0041] Effects of the Invention

[0042] According to the oxygen saturation measurement device, oxygen saturation measurement method, and oxygen saturation measurement program disclosed herein, it is possible to improve measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a perspective view illustrating an oxygen saturation measurement device according to an embodiment of the present disclosure.

[0044] Figure 2 It is a cross-sectional view illustrating a sensor unit of the oxygen saturation measurement device according to the present embodiment.

[0045] Figure 3 : is a block diagram showing the hardware configuration of a processor of the oxygen saturation measurement device according to the present embodiment.

[0046] Figure 4 1 is a flowchart for explaining the oxygen saturation measurement method using the oxygen saturation measurement device according to the present embodiment.

[0047] Figure 5 This is a timing chart for explaining a state in which the emission timings of two measurement lights are determined based on the peak timing and the trough timing of the third pulse wave signal of the reference light in the oxygen saturation measurement method using the oxygen saturation measurement device of the present embodiment.

[0048] Figure 6 This is a diagram for explaining a method of setting the emission timing of two measurement lights based on the peak timing and the trough timing of the third pulse wave signal of the reference light.

[0049] Figure 7 This is a diagram for explaining a method of setting the emission timing of two measurement lights two or more times based on the peak timing and the trough timing of the third pulse wave signal of the reference light.

[0050] Figure 8 It is a diagram for explaining a method of setting a first maximum side light projection period and a first minimum side light projection period for determining the light projection timing of two measurement lights based on a pulsation interval obtained from a third pulse wave signal of reference light.

[0051] Fig. 9 This is a diagram for explaining a method of setting the respective light emission timings of two measurement lights once in the first maximum side light emission period and once in the first minimum side light emission period.

[0052] Fig. 10A This is a diagram for explaining a method of setting a maximum-side threshold value for determining the timing of projection of two measurement lights.

[0053] Fig. 10B This is a diagram for explaining a method of setting a minimum-side threshold value for determining the timing of projection of two measurement lights.

[0054] Fig.11 This is a diagram for explaining a method of setting the respective light emission timings of two measurement lights two or more times in each of the first maximum side light emission period and the first minimum side light emission period.

[0055] Fig.12 It is a graph explaining the change in the amplitude of pulsation accompanying body movement.

[0056] Fig.13 It is a graph explaining the change in the amplitude of the pulsation accompanying breathing.

[0057] Fig.14A This is a diagram for explaining the waveform of a first pulse wave signal obtained from reflected light of red light projected onto an artery of a measurement target.

[0058] Fig. 14B This is a diagram for explaining the waveform of the second pulse wave signal obtained by the reflected light of the infrared light projected onto the artery of the measurement object.

[0059] Fig. 14C This is a diagram for explaining the waveform of the third pulse wave signal obtained from the reflected light of the reference light projected onto the artery of the measurement object. DETAILED DESCRIPTION

[0060] The present embodiment is described below. In the description of the following drawings, the same or similar parts are marked with the same or similar symbols. However, the drawings are schematic, and the relationship between thickness and plane size, the ratio of thickness of each device or each component, etc. are different from reality. Therefore, the specific thickness or size should be determined with reference to the following description. In addition, the drawings also include parts with different dimensional relationships or ratios. In addition, unless otherwise specified in the specification, the number of each component element disclosed in the present invention is not limited to one, and there may be more than two.

[0061] <Oxygen Saturation Measurement Device>

[0062] Reference Figure 1 to Figure 3 The structure of the oxygen saturation measurement device 10 of this embodiment will be described. Figure 1 As shown, the oxygen saturation measurement device 10 of the present embodiment is a portable wearable device that can be worn by a subject and includes a belt 12 , a housing 14 , a sensor unit 16 , a display unit 18 , and a calculation control unit 20 .

[0063] In addition, the oxygen saturation measuring device 10 of the present embodiment is provided with a driving power source 11. The driving power source 11 may be a primary battery or a secondary battery. It should be noted that in the present disclosure, the shape of the oxygen saturation measuring device is not limited to a wearable device that can be worn by the person being measured. The oxygen saturation measuring device of the present disclosure may be portable, whether worn or not, such as portable, which can be close to the wrist, or may be of any configuration such as a fixed type.

[0064] It should be noted that, in this specification, the "direction E in which the forearm extends" overlaps with any of the directions in which the radius of the subject extends, the direction in which the ulna of the subject extends, and the direction in which the artery of the subject extends. In addition, the "direction E in which the forearm extends" is strictly speaking different for each subject. That is, the "direction E in which the forearm extends" is not uniquely determined by coordinates in three-dimensional space, but is independently determined based on the directions in which the radius of the subject extends, the direction in which the ulna of the subject extends, and the direction in which the artery of the subject extends.

[0065] (bring)

[0066] like Figure 1 As shown, the belt 12 is wrapped around the wrist of the subject along the circumferential direction C of the wrist. The raw material of the belt 12 is any material such as resin, cloth, metal, etc. In addition, the belt 12 is provided with a buckle for adjusting and fixing the length when wrapped around the wrist.

[0067] (case)

[0068] The housing 14 is attached to the belt 12 and contacts the surface of the back side (i.e., the back side) of the wrist of the person being measured. The raw material of the housing 14 is any material such as resin or metal. The housing 14 has a certain width along the direction E in which the forearm extends. The housing 14 is provided with a sensor unit 16, a display unit 18, and a calculation control unit 20.

[0069] (Display)

[0070] like Figure 1 As shown, the display unit 18 is arranged on the surface of the housing 14 on the side opposite to the wrist. The display unit 18 is, for example, an image display device formed of a liquid crystal or the like. The display unit 18 displays the calculation result of the calculation control unit 20 to the outside in a manner that the person being measured can visually recognize. A storage device for temporarily storing the measurement result may also be provided in the display unit 18.

[0071] (Sensor unit)

[0072] The sensor unit 16 is mounted on the belt 12. The sensor unit 16 obtains a pulse wave signal of the artery of the wrist, and measures the oxygen saturation of the artery of the wrist based on the obtained pulse wave signal. The sensor unit of this embodiment is placed on the back of the wrist of the person being measured, for example, opposite to the artery included in the dorsal wrist artery network. The dorsal wrist artery network includes branches from the radial artery and branches from the ulnar artery. It should be noted that in the present disclosure, the artery to be measured is not limited to the artery of the wrist.

[0073] like Figure 2 As shown, the sensor unit 16 has: a light emitting portion 16A including a first light emitting element LED1, a second light emitting element LED2 and a third light emitting element LED3; and a light receiving portion 16B including a light receiving element PD. That is, in this embodiment, three light emitting elements and one light receiving element corresponding to the three light emitting elements constitute one "sensor unit". It should be noted that in the present disclosure, more than two sensor units can be provided. In addition, the number of light emitting elements and the number of light receiving elements contained in one "sensor unit" can be set arbitrarily.

[0074] An opening 14A is formed between the light emitting portion 16A in the housing 14 and the outside. An optical device 15A having light transmittance to the light projected from the light emitting element is disposed in the opening 14A. The optical device 15A is, for example, a diffusion lens capable of expanding the irradiation area. In addition, although not shown in the figure, a diffusion agent may be disposed on the upper side of the light emitting element together with or in place of the diffusion lens.

[0075] In addition, an opening 14B is formed between the light receiving portion 16B in the housing 14 and the outside. An optical device 15B that is translucent to the reflected light from the wrist artery is disposed in the opening 14B. The optical device 15B is, for example, a focusing lens that can focus the reflected light. It should be noted that in the present disclosure, the optical device 15A and the optical device 15B are not essential.

[0076] (Light-emitting element)

[0077] The first light emitting element LED1, the second light emitting element LED2 and the third light emitting element LED3 are all electronic components such as light emitting diodes (LEDs). Each light emitting element irradiates light to the artery of the wrist. The first light emitting element LED1, the second light emitting element LED2 and the third light emitting element LED3 are arranged separately from each other. It should be noted that in the present disclosure, the number of the first light emitting element, the second light emitting element and the third light emitting element is one or more, which is arbitrary.

[0078] (First Light Emitting Element and Second Light Emitting Element)

[0079] The first light emitting element LED1 projects red light onto the artery, and the second light emitting element LED2 projects infrared light onto the artery. Figure 2 , the wavelength λ1 of the red light is illustrated on the inner side of the first light emitting element LED1, and the wavelength λ2 of the infrared light is illustrated on the inner side of the second light emitting element LED2. It should be noted that, from the perspective of improving the measurement accuracy, the first light emitting element LED1 and the second light emitting element LED2 are preferably configured so that the optical path lengths of the lights projected by each are as close to the same as possible.

[0080] (Red light and infrared light)

[0081] In the oxygen saturation measurement process, it is necessary to use two wavelength bands with different absorption coefficients of oxyhemoglobin and deoxyhemoglobin in combination. As a combination of wavelength bands, a combination of a red region with a wavelength band of approximately 590 nm to 770 nm and an infrared region with a wavelength band of approximately 770 nm to 1000 nm is preferred.

[0082] In particular, in order to measure oxygen saturation with improved accuracy, it is desirable that the difference between the absorption coefficient of oxyhemoglobin and the absorption coefficient of deoxyhemoglobin be large. Therefore, it is preferred that the peak wavelength of red light is within a range of 640 nm to 660 nm, and the peak wavelength of infrared light is approximately 940 nm. In this embodiment, red light and infrared light are projected intermittently in time, for example, once during one pulsation of the artery.

[0083] (Third Light Emitting Element)

[0084] The third light emitting element LED3 projects reference light having a wavelength with a higher SN ratio with respect to the artery than red light and infrared light. Figure 2 , the wavelength λ3 of the reference light is illustrated on the inner side of the third light emitting element LED3. In this embodiment, the reference light is projected continuously in time, for example, 10 times, 20 times, etc. during one pulsation of the artery. It should be noted that in the present disclosure, as long as the peak moment and the trough moment can be calculated, the number of projections of the reference light can be set arbitrarily.

[0085] (Reference light)

[0086] The reference light has an absorption coefficient of oxygenated hemoglobin and an absorption coefficient of deoxygenated hemoglobin that are higher than the wavelengths of red light and infrared light. In the present embodiment, the SN ratio of the pulse wave signal of the received light corresponding to the reference light obtained by photoplethysmography (PPG) is higher than both the SN ratio of red light and the SN ratio of infrared light. As the reference light, for example, light in a wavelength band of 430 nm to 590 nm, which has a relatively large absorption coefficient in arterial blood, is preferred. Specifically, a blue region with a wavelength band of 430 nm to 490 nm and a green region with a wavelength band of 490 nm to 550 nm are preferred.

[0087] In this embodiment, green light with a peak wavelength of 530 nm to 540 nm is easily absorbed by hemoglobin in the blood and can easily capture the volume change of the arterial blood vessels, so it is preferred in terms of obtaining a pulse wave signal with a relatively high SN. In addition, LED light sources in the wavelength band of green light are highly available in the market and are relatively inexpensive, so they are advantageous as the third light-emitting element for irradiating reference light. It should be noted that in this disclosure, light sources in the wavelength bands of the purple region and ultraviolet region below 430 nm are not excluded as light sources for reference light.

[0088] It should be noted that in the present disclosure, reference light is not limited to green light. In the present disclosure, as long as the absorption coefficient of oxyhemoglobin and deoxyhemoglobin is higher than red light and infrared light, light of any frequency band that can be obtained from the hemoglobin absorption spectrum can be used as reference light.

[0089] (Light receiving element)

[0090] The light receiving element PD is, for example, an electronic component such as a photodiode (PD). The light receiving element PD is arranged at a predetermined position relative to the light emitting element. In the present embodiment, the number of the light receiving element PD is one, but in the present disclosure, the number of the light receiving elements may be two or more.

[0091] The light receiving element PD receives reflected light corresponding to red light, and outputs a first pulse wave signal corresponding to the light intensity of the received reflected light. In addition, the light receiving element PD receives reflected light corresponding to infrared light, and outputs a second pulse wave signal corresponding to the light intensity of the received reflected light. In addition, the light receiving element PD receives reflected light corresponding to reference light, and outputs a third pulse wave signal corresponding to the light intensity of the received reflected light. In the specific measurement of oxygen saturation, two types of reflected light, red light and infrared light, received by the light receiving element are used.

[0092] It should be noted that in the present disclosure, the light receiving element is not limited to the reflected light of each of the red light, the infrared light, and the reference light, and may receive the transmitted light corresponding to each light, and output each pulse wave signal corresponding to the light intensity of the received transmitted light. That is, the oxygen saturation measurement device 10 of the present embodiment is a reflection type that measures the intensity of the pulse wave signal by reflected light, but the present disclosure is not limited to the reflection type, and may constitute a transmission type oxygen saturation measurement device that measures the intensity of the pulse wave signal by transmitted light.

[0093] Although not shown in the figure, a light shielding portion may be provided between the light emitting element and the light receiving element. The light shielding portion prevents the light receiving element from directly receiving the light from the light emitting element.

[0094] (Principle of oxygen saturation measurement)

[0095] Here, the principle of measuring oxygen saturation using two types of irradiation light and two types of reflected light is described. Specifically, the change in the amplitude of the pulse wave signal of the reflected light of red light is monitored over time, and the variable component (in other words, AC) and the fixed component (in other words, DC) of the pulse wave signal contained in the monitored pulse wave signal are calculated. Then, the perfusion index (PI) value of red light is calculated as PI by dividing the variable component by the fixed component (AC / DC). RED In addition, similarly to the case of red light, the PI value (PI) of the reflected light of the near-infrared light is calculated by monitoring the change in the intensity of the pulse wave signal of the reflected light of the near-infrared light over time. IR ).

[0096] Then, calculate the PI value of red light (PI RED ) and the PI value of near infrared light (PI IR ) ratio (PI RED / PI IR Then, the calculated ratio (PI RED / PI IR ) is used in the following formula (1), from which the oxygen saturation can be calculated.

[0097] Oxygen saturation [%] = a × (PI RED / PI IR )+b…Formula (1)

[0098] The coefficients a and b in the formula (1) can be obtained through experiments.

[0099] (Calculation control unit)

[0100] In this embodiment, the calculation control unit 20 is provided in the housing 14. The processor is electrically connected to the first light emitting element, the second light emitting element, the third light emitting element, and the light receiving element PD. Data of the pulse wave signal of the reflected light corresponding to the light projected from each light emitting element is input from the light receiving element PD to the calculation control unit 20 over time. The calculation control unit 20 measures the oxygen saturation of the artery irradiated with light based on the pulse wave signal obtained from the reflected light by a method using a ratio of PI values ​​or the like.

[0101] like Figure 3 As shown, the calculation control unit 20 includes a CPU (Central Processing Unit) 21, a ROM (Read Only Memory) 22, a RAM (Random Access Memory) 23, a memory 24, a user interface 25, and a communication interface 26. Each component is connected via a bus 27 so as to be able to communicate with each other.

[0102] CPU21 is a central processing unit that executes various programs or controls various parts. That is, CPU21 reads programs from ROM22 or memory 24 and uses RAM23 as a work area to execute the programs. CPU21 controls the above-mentioned components and performs various calculations according to the programs recorded in ROM22 or memory 24. CPU21 is a processor of the present disclosure.

[0103] In the present embodiment, an oxygen saturation measurement program is stored in the ROM 22 or the memory 24. The oxygen saturation measurement program is a calculation program for measuring oxygen saturation.

[0104] The ROM 22 stores various programs and various data. The RAM 23 temporarily stores programs and data as a work area. The memory 24 is composed of a HDD (Hard Disk Drive) or an SSD (Solid State Drive), and stores various programs including an operating system and various data.

[0105] The user interface 25 is an interface for a subject wearing the oxygen saturation measurement device 10 as a wearable device to use the calculation control unit 20. The user interface 25 may include, for example, a liquid crystal display having a touch panel that can be touched by the subject, a voice input receiving unit that receives voice input from the subject, and at least one of buttons that can be pressed by the subject. The display unit of this embodiment is an example of the user interface 25.

[0106] The communication interface 26 is an interface for the calculation control unit 20 to communicate with other devices, and uses standards such as Ethernet (registered trademark), FDDI, and Wi-Fi (registered trademark).

[0107] When executing the oxygen saturation measurement program, the oxygen saturation measurement device 10 uses the above-mentioned hardware resources to realize various functions. As the functional components realized by the oxygen saturation measurement device 10, the oxygen saturation measurement device 10 includes a light projection timing determination unit, a light emission control unit, and an oxygen saturation measurement unit. Each functional component is realized by the CPU 21 reading and executing the oxygen saturation measurement program stored in the ROM 22 or the memory 24.

[0108] <Oxygen saturation measurement method>

[0109] Next, refer to Figures 4 to 13 An example of an oxygen saturation level measuring method using the oxygen saturation level measuring device 10 according to the present embodiment will be described.

[0110] First, if Figure 4 As shown in step S1 in FIG. 1 , the processor 21 projects reference light onto the artery of the measurement object via the third light emitting element LED3 .

[0111] Then, if Figure 4 As shown in step S2 in FIG. 1 , the processor 21 receives the received light corresponding to the reference light through the light receiving element PD. The light receiving element PD outputs the third pulse wave signal PS3 corresponding to the received light of the reference light to the processor 21. As a result, Figure 4 As shown in step S3 in , the processor 21 obtains the third pulse wave signal PS3.

[0112] (Light emission timing determination process)

[0113] Then, if Figure 4 As shown in step S4 in the flowchart, the processor 21 determines the first light projection time and the second light projection time based on the peak time and the trough time of the third pulse wave signal PS3.

[0114] Specifically, if Figure 5 As shown, the light projection timing determination unit of the processor 21 calculates the peak timing TM and the trough timing Tm of the third pulse wave signal PS3 in one beat. Then, the processor 21 determines the first light projection timing of the first light emitting element LED1 projecting red light and the second light projection timing of the second light emitting element LED2 projecting infrared light based on the calculated peak timing TM and trough timing Tm.

[0115] (Light Emission Control Processing)

[0116] Then, if Figure 4 As shown in step S5 in FIG. 1 , the processor 21 projects red light at the first light projection time and projects infrared light at the second light projection time. Specifically, the light emission control unit of the processor 21 controls the first light emitting element LED1 and the second light emitting element LED2.

[0117] The light emission control unit causes the first light emitting element LED1 to emit red light at the first light emission timing TF1, and causes the second light emitting element LED2 to emit red light at the second light emission timing TF2. Figure 5 The uppermost section in FIG. 1 illustrates the trajectory of data points of the third pulse wave signal PS3 of the received light corresponding to the reference light and an imaginary line extending vertically downward from the positions of the peak time TM and the trough time Tm extracted from the trajectory.

[0118] Figure 5 The peak time of the uppermost reference light TM, Figure 5 The first light emission time TF1 of the red light in the middle section and Figure 5 The second projection time TF2 of the lowest infrared light in the image is located on the same imaginary line, which means that they are the same time.

[0119] in addition, Figure 5 The trough time Tm of the uppermost reference light in Figure 5 The first light emission time TF1 of the red light in the middle section and Figure 5 The second projection time TF2 of the lowest infrared light in the image is located on the same imaginary line, which means that they are the same time.

[0120] That is, in Figure 5 In the light projection pattern illustrated in the example, the red light and the infrared light are projected synchronously with the peak time TM of the reference light and synchronously with the trough time Tm. Based on the red light projected at the first light projection time TF1, the light receiving element PD outputs the first pulse wave signal PS1. In addition, based on the infrared light projected at the second light projection time TF2, the light receiving element PD outputs the second pulse wave signal PS2.

[0121] (Oxygen saturation measurement processing)

[0122] Then, if Figure 4 As shown in step S6 in FIG. 1 , the processor 21 obtains the first pulse wave signal PS1 corresponding to the red light projected at the first light projection time TF1 and the second pulse wave signal PS2 corresponding to the infrared light projected at the second light projection time TF2. Then, as shown in FIG. Figure 4 As shown in step S7 in FIG. 1 , the oxygen saturation measuring unit of the processor 21 calculates the oxygen saturation of the artery based on the first pulse wave signal PS1 and the second pulse wave signal PS2 output by the light receiving element PD. The calculated oxygen saturation is displayed on the display unit 18 as a measured value.

[0123] (Specific example of light emission timing determination process)

[0124] Next, as specific examples of the above-mentioned light projection timing determination process, process 1 and process 2 in this embodiment are described in detail. Process 1 is a method that mainly uses the pulsation interval of the third pulse wave signal PS3. In addition, process 2 is a method that mainly uses the amplitude of the third pulse wave signal PS3.

[0125] (Process 1)

[0126] First, refer to Figure 6 to Figure 8 Description Processing 1. Figure 6 As shown, the processor 21 calculates the pulsation interval of the predicted pulsation of the third pulse wave signal PS3 that will arrive in the future based on the peak time TM and the trough time Tm of the third pulse wave signal PS3 actually obtained in the past. Figure 6 The uppermost section of FIG. 1 shows the third pulse wave signal PS3 of the reference light. The predicted pulsation interval can be calculated as the average of the pulsation intervals of the plurality of third pulse wave signals PS3 actually obtained. It should be noted that in the present disclosure, the calculation method of the predicted pulsation interval is not limited to the average, and any method can be used.

[0127] In addition, the processor 21 calculates the predicted peak time TEM and the predicted trough time TEm in the predicted pulsation. Figure 6 The second paragraph from the top shows the peak time TM of the reference light and the predicted peak time TEM. Figure 6 The third row from the top in FIG. 1 illustrates the valley time Tm of the reference light and the predicted valley time TEm.

[0128] The predicted peak time TEM can be calculated, for example, by adding the predicted pulse interval to the peak time TM obtained at the current time. Similarly, the predicted trough time TEm can be calculated, for example, by adding the predicted pulse interval to the most recently obtained trough time Tm at the current time. It should be noted that in the present disclosure, the calculation method of the predicted peak time TEM and the predicted trough time TEm is not limited to this, and any method can be used.

[0129] Furthermore, in this embodiment, the processor 21 is configured to determine the first light projection time TF1 and the second light projection time TF2 in the predicted pulsation based on the calculated predicted peak time TEM and predicted trough time TEm. Figure 6 The lowermost section in FIG. 2 illustrates a case where the first light projection timing TF1 of red light and the second light projection timing TF2 of infrared light are set once each based on the peak timing TM and the trough timing Tm, respectively.

[0130] In addition, Figure 6 In the light pattern in , the first light projection time TF1 and the second light projection time TF2 calculated based on the maximum amplitude of the predicted pulsation are earlier than the peak time TM. Figure 6 In the light pattern in , the first light projection time TF1 and the second light projection time TF2 calculated based on the predicted minimum amplitude of the pulsation are later than the trough time Tm. Figure 6 As shown, the first light projection moment TF1 and the second light projection moment TF2 do not need to be strictly synchronized with the peak moment TM and the trough moment Tm respectively, as long as they are determined based on the peak moment TM and the trough moment Tm respectively.

[0131] In addition, if Figure 7 As shown, more than two first light projection moments TF1 and more than two second light projection moments TF2 may also be determined based on the peak moment TM and the trough moment Tm, respectively.

[0132] (First Maximum Side Lighting Period and First Minimum Side Lighting Period)

[0133] In addition, if Figure 8 As shown, in process 1, the processor 21 can also set the first maximum side light projection period DM1 and the first minimum side light projection period Dm1.

[0134] Specifically, the processor 21 sets the period from the peak time TM of the pulsation immediately before the predicted pulsation to the predicted peak time TEM as the first maximum side light projection period DM1 .

[0135] In addition, the processor 21 sets the period from the predicted trough moment TEM of the predicted pulsation to the moment when 1 / 3 of the pulsation interval DE of the predicted pulsation has passed from the predicted trough moment TEM as the first minimum side light projection period Dm1. Furthermore, the processor 21 is configured to determine the first light projection moment TF1 and the second light projection moment TF2 in the set first maximum side light projection period DM1 and the first minimum side light projection period Dm1, respectively.

[0136] When the first light projection time TF1 and the second light projection time TF2 are before the moment of 2 / 3 of the pulsation interval DE, or after the predicted peak time TEM, the value obtained as the maximum amplitude is too far away from the actual maximum amplitude of the artery, so the measurement accuracy is reduced. In addition, when the first light projection time TF1 and the second light projection time TF2 are before the predicted trough time TEm, or after the moment of 1 / 3 of the pulsation interval DE, the value obtained as the minimum amplitude is too far away from the actual minimum amplitude of the artery, so the measurement accuracy is reduced.

[0137] (Process 2)

[0138] Next, refer to Figures 9 to 11 Description Processing 2.

[0139] (Second maximum side light period and second minimum side light period)

[0140] like Fig. 9 As shown, the processor 21 pre-sets the predicted maximum amplitude and the maximum side threshold of the amplitude in the predicted pulsation of the third pulse wave signal PS3 based on the maximum amplitude of the third pulse wave signal PS3 actually obtained before the peak time TM. The predicted maximum amplitude and the maximum side threshold are calculated to determine the first light projection time TF1 and the second light projection time TF2.

[0141] The predicted maximum amplitude can be calculated, for example, by averaging the maximum amplitudes obtained in the past. It should be noted that in the present disclosure, the method for calculating the predicted maximum amplitude is not limited to averaging, and any method can be used. Fig. 10A As shown, the maximum side threshold value can be set to, for example, 2 / 3 or more of the difference between the maximum amplitude and the minimum amplitude of the third pulse wave signal PS3. When the maximum side threshold value is less than 2 / 3 of the difference between the maximum amplitude and the minimum amplitude, the value obtained as the maximum amplitude deviates too much from the actual maximum amplitude of the artery, thereby reducing the measurement accuracy.

[0142] Therefore, the processor 21 is configured to be able to determine the first light projection time TF1 and the second light projection time TF2 when the amplitude of the third pulse wave signal PS3 continuously acquired in time rises to or above the maximum side threshold. In other words, the processor 21 is configured to be unable to determine the first light projection time TF1 and the second light projection time TF2 when the amplitude of the third pulse wave signal PS3 that changes exceeds the maximum threshold and begins to decrease and then reaches a state less than the maximum side threshold. As a result, in the actual pulsation of the third pulse wave signal PS3, a second maximum side light projection period DM2 with an amplitude greater than the maximum side threshold is formed.

[0143] In addition, the processor 21 pre-sets the predicted minimum amplitude and the minimum side threshold value of the amplitude in the predicted pulsation of the third pulse wave signal PS3 based on the minimum amplitude of the third pulse wave signal PS3 actually obtained before the trough time Tm. The predicted minimum amplitude and the minimum side threshold value are calculated to determine the first light projection time TF1 and the second light projection time TF2.

[0144] The predicted minimum amplitude can be calculated, for example, by averaging the minimum amplitudes obtained in the past. It should be noted that in the present disclosure, the calculation method of the predicted minimum amplitude is not limited to averaging, and any method can be used. Fig. 10B As shown, the minimum side threshold value can be set to, for example, 1 / 3 or less of the difference between the maximum amplitude and the minimum amplitude of the third pulse wave signal PS3. When the minimum side threshold value exceeds 1 / 3 of the difference between the maximum amplitude and the minimum amplitude, the value obtained as the minimum amplitude deviates too much from the actual minimum amplitude of the artery, thereby reducing the measurement accuracy.

[0145] Therefore, the processor 21 is configured to be able to determine the first light projection time TF1 and the second light projection time TF2 when the amplitude of the third pulse wave signal PS3 continuously obtained in time drops below the minimum side threshold. In other words, the processor 21 is configured to be unable to determine the first light projection time TF1 and the second light projection time TF2 when the amplitude of the third pulse wave signal PS3 that changes exceeds the minimum threshold and starts to rise and reaches a state exceeding the minimum side threshold. As a result, in the actual pulsation of the third pulse wave signal PS3, a second minimum side light projection period Dm2 with an amplitude below the minimum side threshold is formed.

[0146] In addition, if Fig.11 As shown, more than two first light projection times TF1 and more than two second light projection times TF2 may be respectively determined during the second maximum side light projection period DM2 and the second minimum side light projection period Dm2.

[0147] (Switching between process 1 and process 2)

[0148] In this embodiment, the process 1 and the process 2 can be switched based on the variation coefficient representing the pulsation state of the measured person. Specifically, the processor 21 calculates the variation coefficient based on the pulsation interval of the third pulse wave signal PS3 actually obtained in the past. The variation coefficient can be calculated by, for example, dividing the standard deviation of the pulsation interval in a certain pulse number such as 10 beats obtained in the past by the average value of the pulsation interval in the certain pulse number. It should be noted that in the present disclosure, the number of beats used to calculate the variation coefficient is not limited to 10 beats.

[0149] Then, the processor 21 is configured to execute a determination method based on the pulsation interval (processing 1) when the calculated variation coefficient is below a preset threshold value, and to execute a determination method based on the amplitude (processing 2) when the variation coefficient exceeds the threshold value.

[0150] (Threshold)

[0151] In the present embodiment, the threshold value of the coefficient of variation is 0.1 or less. It should be noted that the present disclosure is not limited to this, and can be appropriately changed.

[0152] Here, when there is a variation in the beat interval such as arrhythmia, the measurement accuracy may be reduced in the determination method based on the beat interval (process 1). Therefore, in this embodiment, the threshold is set to determine whether there is a variation in the beat interval.

[0153] When it is determined that there is a high possibility of a variation in the pulsation interval due to the variation coefficient exceeding the threshold, (processing 1) is not executed but (processing 2) based on the amplitude is executed. Therefore, it is possible to improve the measurement accuracy of the oxygen saturation.

[0154] On the other hand, in the case of the determination method based on amplitude (process 2), if the amplitude changes due to the subject's breathing, body movement, etc., the measurement accuracy of the oxygen saturation may decrease. Fig.12 In FIG. 1 , as an example of amplitude change accompanying body movement, a pulse wave signal in which baseline change is indicated by two or more arrows is illustrated. Fig.13 , a pulse wave signal in which a baseline variation is indicated by two or more arrows is illustrated as an example of an amplitude variation accompanying breathing.

[0155] Therefore, in this embodiment, when it is determined that the possibility of the pulse interval deviation is low because the coefficient of variation is below the threshold, (processing 2) is not performed and (processing 1) based on the pulse interval is performed. As a result, the influence of amplitude changes caused by breathing, body movement, etc. on oxygen saturation measurement can be suppressed.

[0156] (Comparative Example)

[0157] On the other hand, in the comparative example where only red light and infrared light are projected as in the present embodiment, the number of times each of the red light and infrared light is projected increases in order to obtain the maximum amplitude and the minimum amplitude of each of the red light and infrared light. Therefore, the input power in the light projection increases. Therefore, in the comparative example, the red light and infrared light need to be repeated more than twice, for example, several dozen times in one pulsation of the artery, at an interval shorter than the pulsation interval.

[0158] In addition, Fig. 14B The red light and Fig. 14C The waveforms of the pulse wave signals corresponding to the infrared light shown in the example are compared with Fig.14A The waveform of the pulse wave signal corresponding to the reference light illustrated in the example is unclear. Therefore, the degree of amplitude calculation becomes low, and as a result, the measurement accuracy of the oxygen saturation level decreases.

[0159] (Effect)

[0160] In this embodiment, the wavelength of the reference light projected to the artery is a wavelength at which the absorption coefficient of oxygenated hemoglobin and the absorption coefficient of deoxygenated hemoglobin are higher than those of red light and infrared light. Therefore, the SN ratio of the third pulse wave signal PS3 corresponding to the reference light is higher than that of the first pulse wave signal PS1 corresponding to the red light and the second pulse wave signal PS2 corresponding to the infrared light. In addition, based on the peak time TM and the trough time Tm of the third pulse wave signal PS3 in one beat, the first light projection time TF1 for projecting the red light and the second light projection time TF2 for projecting the infrared light are determined.

[0161] Then, the oxygen saturation of the artery is measured based on the first pulse wave signal PS1 output by the light receiving element PD based on the red light projected at the first light projection timing TF1 and the second pulse wave signal PS2 output by the light receiving element PD based on the infrared light projected at the second light projection timing TF2.

[0162] In the waveform of the third pulse wave signal PS3 in one beat, the peak value on the maximum side of the amplitude, i.e., the maximum amplitude, is obtained at the peak time TM, and the peak value on the minimum side of the amplitude, i.e., the minimum amplitude, is obtained at the trough time Tm. Therefore, by projecting the red light for measurement at the first light projection time TF1 determined based on the peak time TM and the trough time Tm, the calculation accuracy of the amplitude of the first pulse wave signal PS1 of the received light corresponding to the red light is improved.

[0163] Similarly, by projecting the infrared light for measurement at the second projection time TF2 determined based on the peak time TM and the trough time Tm, the calculation accuracy of the amplitude of the second pulse wave signal PS2 of the received light corresponding to the infrared light is improved. As a result, the measurement accuracy of the oxygen saturation measured based on the first pulse wave signal PS1 and the second pulse wave signal PS2 is improved.

[0164] In addition, in the present embodiment, the first light projection time TF1 and the second light projection time TF2 are determined based on the peak time TM and the trough time Tm formed once in one pulsation. That is, the number of light projections may be at least two times based on the peak time TM and the trough time Tm. Therefore, compared with the case where the red light and the infrared light are each projected on the artery of the object of measurement twice or more at an interval shorter than the pulsation interval, such as 50 times, in one pulsation, the input power can be reduced. In addition, the number of light projections and the number of light receptions of the red light and the infrared light can be suppressed.

[0165] In addition, in this embodiment, the input power consumed for the projection of red light and infrared light is reduced, and the life of the measuring device can be extended accordingly. In addition, if the reduced input power is restored to the projection power of red light and the projection power of infrared light within a range that ensures a certain measurement accuracy, the SN ratio of red light and the SN ratio of infrared light can be improved. As a result, the measurement accuracy of oxygen saturation can be further improved.

[0166] In addition, in the present embodiment, the predicted peak time TEM and predicted trough time TEm in the predicted pulsation are calculated based on the peak time TM and trough time Tm of the third pulse wave signal PS3 actually acquired.

[0167] Based on the calculated predicted peak time TEM and predicted trough time TEm, the first light projection time TF1 and the second light projection time TF2 in the predicted pulsation are determined. Therefore, the first light projection time TF1 and the second light projection time TF2 can be determined with improved accuracy.

[0168] In addition, in the present embodiment, the period from the peak moment TM of the pulsation immediately before the predicted pulsation to the moment of 2 / 3 of the pulsation interval DE of the predicted pulsation and to the predicted peak moment TEM is set as the first maximum side light projection period DM1. In addition, the period from the predicted trough moment TEm of the predicted pulsation and to the moment of 1 / 3 of the pulsation interval DE of the predicted pulsation from the predicted trough moment TEm is set as the first minimum side light projection period Dm1. In addition, in the set first maximum side light projection period DM1 and the first minimum side light projection period Dm1, the first light projection moment TF1 and the second light projection moment TF2 are respectively determined. Therefore, the first light projection moment TF1 and the second light projection moment TF2 can be determined with further improved accuracy.

[0169] In addition, in this embodiment, based on the maximum amplitude of the third pulse wave signal PS3 actually obtained at the peak moment, a maximum side threshold value for determining the amplitude of the first light projection moment TF1 and the second light projection moment TF2 is set. In addition, a second maximum side light projection period DM2 is set in which the amplitude in the predicted pulsation of the third pulse wave signal PS3 is greater than the maximum side threshold value.

[0170] In addition, based on the minimum amplitude of the third pulse wave signal PS3 actually obtained at the trough moment, a minimum side threshold for determining the amplitude of the first light projection moment TF1 and the second light projection moment TF2 is set. In addition, a second minimum side light projection period is set in which the amplitude of the predicted pulsation of the third pulse wave signal PS3 is greater than the minimum side threshold.

[0171] Then, the first light projection timing TF1 and the second light projection timing TF2 are determined during the set second maximum side light projection period DM2 and the second minimum side light projection period, respectively. Therefore, the first light projection timing TF1 and the second light projection timing TF2 can be determined with improved accuracy.

[0172] In addition, in this embodiment, the maximum side threshold is greater than 2 / 3 of the difference between the maximum amplitude and the minimum amplitude of the third pulse wave signal PS3, and the minimum side threshold is less than 1 / 3 of the difference between the maximum amplitude and the minimum amplitude of the third pulse wave signal PS3. Therefore, the first light projection time TF1 and the second light projection time TF2 can be determined with further improved accuracy.

[0173] In addition, in the present embodiment, a coefficient of variation indicating the pulsation state of the subject is calculated based on the pulsation interval of the third pulse wave signal PS3 actually obtained. In addition, when the calculated coefficient of variation is below a preset threshold value, the processor 21 determines the first light projection time TF1 and the second light projection time TF2 in the first maximum side light projection period DM1 and the first minimum side light projection period Dm1, respectively, by executing (processing 1).

[0174] In addition, when the coefficient of variation exceeds the threshold, the processor 21 determines the first light projection time TF1 and the second light projection time TF2 during the second maximum side light projection period DM2 and the second minimum side light projection period, respectively, by executing (processing 2). That is, the method of determining the first light projection time TF1 and the second light projection time TF2 is switched according to the pulse state of the person being measured. Therefore, the preferred oxygen saturation measurement process can be selected according to the pulse state of the person being measured.

[0175] In addition, in the present embodiment, the threshold value of the coefficient of variation is set within 0.1. Therefore, the switching accuracy of the oxygen saturation level measurement process can be improved.

[0176] In addition, in the case of a measuring device such as a wearable device driven by a relatively small primary battery or secondary battery, it is difficult to increase the light projection power each time because it is necessary to avoid shortening the continuous use time. However, in this embodiment, by suppressing the calculation load, it is possible to reduce the input power. Therefore, it is possible to realize a wearable device that can achieve a long life.

[0177] <Other Implementation Methods>

[0178] The present disclosure has been described through the above-disclosed embodiments; however, the description and drawings constituting a part of this disclosure should not be construed as limiting the present disclosure.

[0179] For example, in the present disclosure, the oxygen saturation measurement process executed by reading software (program) into the CPU 21 in the above-mentioned embodiment may be executed by various processors other than the CPU. As the processor in this case, there can be exemplified a processor having a circuit configuration specially designed for executing a specific process, such as a PLD (Programmable Logic Device) (FPGA) (Field-Programmable Gate Array) (Field Programmable Gate Array) (Application Specific Integrated Circuit) (ASIC) (Application Specific Integrated Circuit ...

[0180] In addition, the oxygen saturation measurement process may be executed by one of these various processors, or by a combination of two or more processors of the same or different types (for example, two or more FPGAs, a combination of a CPU and an FPGA, etc.). In addition, more specifically, the hardware structure of these various processors is a circuit that combines circuit elements such as semiconductor elements.

[0181] In addition, in the above-mentioned embodiments, the oxygen saturation measurement program is pre-stored (installed) in the ROM 22 or the memory 24, but the present invention is not limited thereto. The program may be provided in a recording medium such as a CD-ROM (Compact Disk Read Only Memory), a DVD-ROM (Digital Versatile Disk Read Only Memory), or a USB (Universal Serial Bus) memory. In addition, the program may be downloaded from an external device via a network.

[0182] The present disclosure includes various embodiments and the like that are not described above, and the technical scope of the present disclosure is determined only by the technical features of the inventions in the claims that are appropriate based on the above description.

[0183] The disclosure of Japanese Patent Application No. 2022-167840 filed on October 19, 2022 is incorporated herein by reference in its entirety.

[0184] In addition, all documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each document, patent application, and technical standard was specifically and individually described as being incorporated by reference.

Claims

1. An oxygen saturation measuring device, comprising: A sensor unit comprising: a first light emitting element that projects red light onto an artery; a second light emitting element that projects infrared light onto the artery; a third light emitting element that projects reference light onto the artery, the reference light having an absorption coefficient of oxyhemoglobin and an absorption coefficient of deoxyhemoglobin that are higher than the wavelength of red light and infrared light; and a light receiving element that receives transmitted light or reflected light corresponding to the projected red light, infrared light, and reference light, respectively, as received light, and outputs a first pulse wave signal corresponding to the light intensity of the received red light, a second pulse wave signal corresponding to the light intensity of the received infrared light, and a third pulse wave signal corresponding to the light intensity of the received reference light; and A processor is electrically connected to the first light-emitting element, the second light-emitting element and the light-receiving element, and determines a first light-emitting time when the first light-emitting element projects red light and a second light-emitting time when the second light-emitting element projects infrared light based on the peak time and the trough time of the third pulse wave signal in one beat, causes the first light-emitting element to project red light at the determined first light-emitting time, and causes the second light-emitting element to project infrared light at the determined second light-emitting time, and calculates oxygen saturation based on a first pulse wave signal obtained based on the light intensity of received light of the red light projected at the first light-emitting time and a second pulse wave signal obtained based on the light intensity of received light of the infrared light projected at the second light-emitting time, thereby measuring the oxygen saturation of the artery.

2. The oxygen saturation measurement device according to claim 1, wherein: The processor is composed of: Based on the peak time and the trough time of the acquired third pulse wave signal, the pulsation interval of the predicted pulsation of the third pulse wave signal to be expected, the predicted peak time and the predicted trough time in the predicted pulsation are calculated, Based on the calculated predicted peak time and the predicted trough time, the first light projection time and the second light projection time in the predicted pulsation are determined.

3. The oxygen saturation measuring device according to claim 2, wherein: The processor is composed of: a first maximum sidelight period from the peak time of the pulsation immediately before the predicted pulsation to the predicted peak time after a time of 2 / 3 of the pulsation interval of the predicted pulsation, and a first minimum side light projection period after the predicted trough time of the predicted pulsation and before a time when 1 / 3 of the pulsation interval of the predicted pulsation has passed from the predicted trough time, The first light projection moment and the second light projection moment are determined respectively.

4. The oxygen saturation measurement device according to claim 1, wherein: The processor is composed of: Based on the maximum amplitude of the third pulse wave signal obtained at the peak time, a maximum side threshold of the amplitude is set, Based on the minimum amplitude of the third pulse wave signal obtained at the trough time, a minimum side threshold of the amplitude is set, During the pulsation of the third pulse wave signal, the first light projection timing and the second light projection timing are respectively determined during a second maximum side light projection period when the amplitude is greater than or equal to the maximum side threshold and during a second minimum side light projection period when the amplitude is less than or equal to the minimum side threshold.

5. The oxygen saturation measurement device according to claim 4, wherein: The maximum side threshold is greater than 2 / 3 of the difference between the maximum amplitude and the minimum amplitude, The minimum side threshold is less than 1 / 3 of the difference between the maximum amplitude and the minimum amplitude.

6. The oxygen saturation measurement device according to claim 1, wherein: The processor is composed of: Based on the obtained pulsation interval of the third pulse wave signal, a coefficient of variation indicating the state of pulsation is calculated, When the calculated variation coefficient is less than a preset threshold value, the following process 1 is executed: When the coefficient of variation exceeds the threshold, the following process 2 is performed: (Process 1) Based on the peak time and the trough time of the acquired third pulse wave signal, the pulsation interval of the predicted pulsation of the third pulse wave signal to be expected, the predicted peak time and the predicted trough time in the predicted pulsation are calculated, Determining the first light projection time and the second light projection time in the predicted pulsation based on the calculated predicted peak time and the predicted trough time; (Process 2) Based on the maximum amplitude of the third pulse wave signal obtained at the peak time, a maximum side threshold of the amplitude is set, Based on the minimum amplitude of the third pulse wave signal obtained at the trough time, a minimum side threshold of the amplitude is set, During the pulsation of the third pulse wave signal, the first light projection timing and the second light projection timing are respectively determined during a second maximum side light projection period when the amplitude is greater than or equal to the maximum side threshold and during a second minimum side light projection period when the amplitude is less than or equal to the minimum side threshold.

7. The oxygen saturation measuring device according to claim 6, wherein: The threshold value of the coefficient of variation is 0.1 or less. 8 . The oxygen saturation measurement device according to claim 1 , which is a wearable device that can be worn by a person being measured.

9. A method for measuring oxygen saturation, wherein: projecting a reference light onto the artery, the reference light having a wavelength whose absorption coefficient of oxygenated hemoglobin and absorption coefficient of deoxygenated hemoglobin are higher than those of red light and infrared light, receiving transmitted light or reflected light corresponding to the projected reference light as received light, acquiring a third pulse wave signal corresponding to the light intensity of the received light of the reference light, Based on the peak moment and the trough moment of the third pulse wave signal in one beat, a first light projection moment of red light and a second light projection moment of infrared light are determined. projecting red light at the determined first light projection moment, projecting infrared light at the determined second light projection time, The oxygen saturation of the artery is measured by calculating the oxygen saturation based on a first pulse wave signal obtained based on the light intensity of received light of the transmitted light or reflected light corresponding to the red light projected at the first light projection moment, and a second pulse wave signal obtained based on the light intensity of received light of the transmitted light or reflected light corresponding to the infrared light projected at the second light projection moment.

10. An oxygen saturation measurement program, which causes a processor to execute the following processing: projecting reference light onto the artery, the reference light having a wavelength at which the absorption coefficient of oxygenated hemoglobin and the absorption coefficient of deoxygenated hemoglobin are higher than those of red light and infrared light; receiving transmitted light or reflected light corresponding to the projected reference light as received light; acquiring a third pulse wave signal corresponding to the light intensity of the received light of the reference light; Determine a first light-casting time for projecting red light and a second light-casting time for projecting infrared light based on the obtained peak time and trough time of the third pulse wave signal in one beat; Projecting red light at the determined first light projection time; Projecting infrared light at the determined second light projection time; as well as The oxygen saturation of the artery is measured by calculating the oxygen saturation based on a first pulse wave signal obtained based on the light intensity of received light of the transmitted light or reflected light corresponding to the red light projected at the first light projection moment, and a second pulse wave signal obtained based on the light intensity of received light of the transmitted light or reflected light corresponding to the infrared light projected at the second light projection moment.

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