Pulse wave signal measurement device, pulse wave signal measurement method, and oxygen saturation measurement device

Abstract

This oxygen saturation measurement device comprises: a first light projection element; a second light projection element; a first light-receiving element that is disposed in a state where a first optical path having a first distance is formed between the first light projection element and the first light-receiving element and that is disposed in a state where a second optical path having a second distance different from the first distance is formed between the second light projection element and the first light-receiving element, the first light-receiving element receiving respective reflected light corresponding to light projected from the first light projection element or the second light projection element; and a second light-receiving element that is disposed in a state where a third optical path having the first distance is formed between the first light projection element and the second light-receiving element and / or a state where a fourth optical path having the second distance is formed between the second light projection element and the second light-receiving element, the second light-receiving element receiving respective reflected light corresponding to light projected from the first light projection element or the second light projection element.

Description

Pulse wave signal measuring device, pulse wave signal measuring method, and oxygen saturation measuring device

[0001] The present disclosure relates to a pulse wave signal measuring device, a pulse wave signal measuring method, and an oxygen saturation measuring device.

[0002] Conventionally, oxygen saturation in arterial blood (S Ｐ O ２ As an example of a method for measuring erythrocyte erythrocyte count (EC), a measurement method using absorption spectroscopy is known, as disclosed in U.S. Patent Publication No. 10,215,698. In a measurement method using absorption spectroscopy, red light and infrared light having different wavelengths are projected onto arterial blood by a light-projecting element, and transmitted light or reflected light corresponding to each light is received by a light-receiving element. For ease of explanation, the light received by the light-receiving element, such as transmitted light and reflected light, will hereinafter be collectively referred to as "received light."

[0003] In a specific measurement, for example, multiple amplitudes of the pulse wave signal for red light and infrared light are measured from the maximum and minimum values ​​obtained from the pulse wave signal of received light. The fluctuating component (AC) and fixed component (DC) of the pulse wave signal are calculated from the multiple measured amplitudes, and the perfusion index (PI value) for red light and infrared light is calculated from the calculated fluctuating component and fixed component. The ratio of the PI value for red light to the PI value for infrared light (absorbance ratio) is then introduced into a preset formula for calculating oxygen saturation, thereby calculating the measured oxygen saturation.

[0004] As a technique for measuring a pulse wave signal, U.S. Patent Publication No. 10,215,698 discloses a pulse wave signal measuring device that includes a light-projecting element that forms a plurality of optical paths, including at least two optical paths, and a light-receiving element that receives reflected light from the light-projecting element that passes through each of the at least two optical paths. In this regard, a new technique that can improve the measurement accuracy of a pulse wave signal is desired.

[0005] Patent Document 1: U.S. Patent Publication No. 10,215,698

[0006] The present disclosure provides a pulse wave signal measuring device, a pulse wave signal measuring method, and an oxygen saturation measuring device that can improve the measurement accuracy of a pulse wave signal.

[0007] An oxygen saturation measurement device according to a first aspect of the present disclosure includes a first light-emitting element that projects light onto an artery, a second light-emitting element that is disposed apart from the first light-emitting element and projects light onto the artery, a first light-receiving element that is disposed so as to form a first optical path with a first distance between it and the first light-emitting element and so as to form a second optical path with a second distance between it and the second light-emitting element that is different from the first distance, and that receives reflected light corresponding to the light projected from the first light-emitting element or the second light-emitting element, a second light-receiving element disposed in at least one of a state in which a third optical path having the first distance is formed between the first light-projecting element and the second light-projecting element, and a state in which a fourth optical path having the second distance is formed between the second light-projecting element and the second light-projecting element, and receiving reflected light corresponding to the light projected from the first light-projecting element or the second light-projecting element, respectively; and a second measurement unit electrically connected to the second light-receiving element and capable of measuring a second pulse wave signal corresponding to the optical intensity of the reflected light corresponding to the light projected from the first light-projecting element or the second light-projecting element.

[0008] According to the first aspect, a first optical path forming a first distance and a second optical path forming a second distance different from the first distance are formed. This improves the measurement accuracy of the pulse wave signal compared to when an optical path having only one distance is used to measure the pulse wave signal. Furthermore, two optical paths having a common distance for at least one of the first distance and the second distance are formed. This improves the measurement accuracy of the pulse wave signal compared to when only one optical path is used to measure the pulse wave signal for one distance.

[0009] In addition, in a second aspect, the first aspect is provided with a control unit that can switch between emitting light from the first light-emitting element and emitting light from the second light-emitting element depending on the value of a preset index related to the measurement state.

[0010] According to the above configuration, it is possible to switch between light emission from the first light-emitting element and light emission from the second light-emitting element.

[0011] In addition, in a third aspect, in the second aspect, the control unit selectively switches between emitting light from the first light-emitting element and emitting light from the second light-emitting element depending on the relationship between the value of the index and a preset threshold value related to the measurement state.

[0012] With this configuration, the optical path having either the relatively long or shortest distance between the first distance and the second distance is selected. The pulse wave signal measuring device is then controlled to measure only the pulse wave signal of the reflected light passing through the selected optical path. This facilitates power saving according to the measurement conditions.

[0013] In addition, in a fourth aspect, in any of the first to third aspects, when the arrangement pattern of the first light-emitting element, the second light-emitting element, the first light-receiving element, and the second light-receiving element is set as a basic array, multiple basic arrays are formed by one or more first light-emitting elements, one or more second light-emitting elements, one or more first light-receiving elements, and one or more second light-receiving elements, and the first light-emitting element, the second light-emitting element, the first light-receiving element, and the second light-receiving element are arranged so that the optical paths of adjacent basic arrays in a planar view are formed apart without overlapping.

[0014] According to the above configuration, it is possible to prevent a large decrease in overall measurement accuracy caused by multiple three-dimensional actual optical paths overlapping in a measurement region where a large measurement error is likely to occur.

[0015] In addition, in a fifth aspect, in any of the first to fourth aspects, when the arrangement pattern of the first light-emitting element, the second light-emitting element, the first light-receiving element, and the second light-receiving element is set as a basic array, multiple basic arrays are formed by one or more of the first light-emitting elements, one or more of the second light-emitting elements, one or more of the first light-receiving elements, and one or more of the second light-receiving elements, and in the basic arrays that are adjacent in a planar view, at least one of the first light-emitting element, the second light-emitting element, the first light-receiving element, and the second light-receiving element is shared.

[0016] The above configuration improves the efficiency of light utilization from the light source, promotes low power consumption in the pulse wave signal measuring device, and reduces the area of ​​the measurement region.

[0017] In addition, in a sixth aspect, in the fifth aspect, the second light receiving element is arranged in a state in which a third optical path having the first distance is formed between it and the first light emitting element, and in a state in which a fourth optical path having the second distance is formed between it and the second light emitting element, so that in a planar view, multiple basic arrays having a rectangular shape are formed, the first light emitting element is located at a vertex where sides having a common length of the first distance intersect, the second light emitting element is located at a vertex where sides having a common length of the second distance intersect, and the first light receiving element or the second light receiving element is located at a vertex where a side having the length of the first distance and a side having the length of the second distance intersect.

[0018] According to the above configuration, four optical paths can be realized, including the first optical path and the third optical path having a common first distance, and the second optical path and the fourth optical path having a common second distance.

[0019] A seventh aspect of the present invention provides a pulse wave signal measuring method including: a first light-emitting element that projects light onto an artery; a second light-emitting element that is positioned apart from the first light-emitting element and projects light onto the artery; a first light-receiving element that is disposed so as to form a first optical path having a first distance between it and the first light-emitting element and so as to form a second optical path having a second distance between it and the second light-emitting element that is different from the first distance, and that receives reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element; a first measuring unit that is electrically connected to the first light-receiving element and is capable of measuring a first pulse wave signal according to the light intensity of the reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element; and a first measuring unit that measures at least one of a state in which a third optical path having the first distance between it and the first light-emitting element and a state in which a fourth optical path having the second distance between it and the second light-emitting element are formed. a second light-receiving element arranged in either one of the two states and receiving reflected light corresponding to light emitted from the first light-emitting element or the second light-emitting element, respectively; a second measurement unit electrically connected to the second light-receiving element and capable of measuring a second pulse wave signal according to the light intensity of the reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element, respectively; and a control unit capable of selectively switching between light emission by the first light-emitting element and light emission by the second light-emitting element, using a pulse wave signal measuring device comprising: a first light-emitting element, a second light-receiving element arranged in either one of the two states and receiving reflected light corresponding to light emitted from the first light-emitting element or the second light-emitting element, a second measurement unit electrically connected to the second light-receiving element and capable of measuring a second pulse wave signal according to the light intensity of the reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element,

[0020] As with the first aspect, this configuration improves the measurement accuracy of the pulse wave signal compared to when an optical path having only one distance is used to measure the pulse wave signal. Also, this configuration improves the measurement accuracy of the pulse wave signal compared to when only one optical path per distance is used to measure the pulse wave signal.

[0021] An oxygen saturation measuring device according to an eighth aspect includes a first light-emitting element that projects light onto an artery, a second light-emitting element that is disposed apart from the first light-emitting element and projects light onto the artery, a first light-receiving element that is disposed so as to form a first optical path having a first distance between it and the first light-emitting element and so as to form a second optical path having a second distance different from the first distance between it and the second light-emitting element, and that receives reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element, respectively, a first measuring unit that is electrically connected to the first light-receiving element and is capable of measuring a first pulse wave signal according to the light intensity of the reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element, and a state in which a third optical path having the first distance is formed between it and the first light-emitting element and the second light-emitting element, a second light-receiving element that receives reflected light corresponding to light projected from the first light-projecting element or the second light-projecting element, the second light-receiving element being disposed in at least one of the states where a fourth optical path having the second distance is formed between the first light-projecting element and the second light-projecting element; a second measurement unit that is electrically connected to the second light-receiving element and is capable of measuring a second pulse wave signal according to the light intensity of the reflected light corresponding to the light projected from the first light-projecting element or the second light-projecting element; and a processor that is electrically connected to the first measurement unit and the second measurement unit and that measures the oxygen saturation of the artery by calculating the oxygen saturation based on the first pulse wave signal and the second pulse wave signal.

[0022] According to the above configuration, the oxygen saturation level can be calculated based on the first pulse wave signal and the second pulse wave signal that are measured with high accuracy, thereby improving the accuracy of measuring the oxygen saturation level.

[0023] In a ninth aspect, as in the eighth aspect, the processor compares the attribute data of the first pulse wave signal and the second pulse wave signal with a predetermined standard to determine the reliability of the pulse wave signals, and calculates the oxygen saturation level using the pulse wave signal having the attribute data determined to satisfy the standard.

[0024] According to the above configuration, the accuracy of measuring oxygen saturation is further improved.

[0025] The pulse wave signal measuring device, pulse wave signal measuring method, and oxygen saturation measuring device according to the present disclosure can improve the measurement accuracy of the pulse wave signal.

[0026] 1 is a perspective view illustrating an oxygen saturation measurement device provided with a pulse wave signal measurement device according to an embodiment of the present disclosure. FIG. 2 is a perspective view illustrating the state of a measurement region for a pulse wave signal when the oxygen saturation measurement device according to the embodiment is worn on the wrist of a person being measured. FIG. 3 is a block diagram comprehensively illustrating the hardware configuration of a processor of the pulse wave signal measurement device and the oxygen saturation measurement device according to the embodiment. FIG. 4 is a block diagram illustrating the hardware configuration of a processor of the pulse wave signal measurement device and the oxygen saturation measurement device according to the embodiment based on function. FIG. 5 is a plan view illustrating the arrangement pattern of light-projecting elements and light-receiving elements of a pulse wave signal measurement device according to the embodiment, which has two optical paths. FIG. 6 is a plan view illustrating drive control of the light-projecting elements and light-receiving elements of a pulse wave signal measurement device according to the embodiment, which has two optical paths. FIG. 7 is a plan view illustrating the arrangement pattern of light-projecting elements and light-receiving elements according to a first modified example having two optical paths. FIG. 8 is a plan view illustrating drive control of the light-projecting elements and light-receiving elements according to the first modified example having two optical paths. FIG. 9 is a plan view illustrating the arrangement pattern of light-projecting elements and light-receiving elements according to a second modified example having two optical paths. FIG. 10 is a plan view illustrating drive control of the light-projecting elements and light-receiving elements according to the second modified example having two optical paths. FIG. 10 is a plan view illustrating the arrangement pattern of light projecting elements and light receiving elements according to a third modified example having two optical paths. FIG. 11 is a plan view illustrating the arrangement pattern of light projecting elements and light receiving elements according to a fourth modified example having two optical paths. FIG. 12 is a plan view illustrating the arrangement pattern of light projecting elements and light receiving elements according to a fifth modified example having two optical paths. FIG. 13 is a plan view illustrating the arrangement pattern of light projecting elements and light receiving elements according to a sixth modified example having two optical paths. FIG. 14 is a plan view illustrating the arrangement pattern of light projecting elements and light receiving elements according to a seventh modified example having two optical paths. FIG. 15 is a plan view illustrating the arrangement pattern of light projecting elements and light receiving elements according to an eighth modified example having three optical paths. FIG. 16 is a flow chart illustrating a pulse wave signal measurement method using a pulse wave signal measurement device according to the present embodiment, and an oxygen saturation measurement method using an oxygen saturation measurement device, the flow chart illustrating a process of selecting an optical path using the amount of received light as an index related to the measurement state, and a process of determining the reliability of the pulse wave signal.10 is a flowchart illustrating a process for selecting an optical path using a perfusion index value as an index related to the measurement state and a process for determining the reliability of a pulse wave signal in a method for measuring a pulse wave signal and a method for measuring oxygen saturation according to another example. 11 is a flowchart illustrating a process for selecting an optical path using both the amount of received light and the perfusion index value as indexes related to the measurement state and a process for determining the reliability of a pulse wave signal in a method for measuring a pulse wave signal and a method for measuring oxygen saturation according to yet another example.

[0027] Embodiments of the present disclosure are described below. However, the present disclosure is not limited to the following embodiments. When embodiments are described with reference to drawings in the present disclosure, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of components in each drawing are conceptual, and the relative size relationships between components are not limited to these. In the following description of the drawings, identical and similar parts are denoted by the same or similar symbols. However, the drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratios of each device and each component, etc., differ from the actual ones. Therefore, specific thicknesses and planar dimensions should be determined with reference to the following explanation. Furthermore, parts with different dimensional relationships and ratios are included between the drawings. Furthermore, unless otherwise specified in the specification, the number of each component element of the present disclosure is not limited to one and may be present in multiple numbers. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges and do not limit the present disclosure.

[0028] <Pulse Wave Signal Measuring Device and Oxygen Saturation Measuring Device> The structure of an oxygen saturation measuring device 10 according to this embodiment will be described with reference to Figures 1 to 10. As shown in Figure 1, the oxygen saturation measuring device 10 according to this embodiment is a portable wearable device that can be worn by a person being measured, and includes a band 12, a housing 14, a PPG sensor unit 16, a display unit 18, and an arithmetic and control unit 20.

[0029] The oxygen saturation measuring device 10 of this embodiment measures oxygen saturation using a pulse wave signal measured by a pulse wave signal measuring device 30. The oxygen saturation measuring device 10 of this embodiment is configured integrally with the pulse wave signal measuring device 30. In the present disclosure, the pulse wave signal measuring device does not necessarily have to be configured integrally with the oxygen saturation measuring device, and may be configured as a standalone device.

[0030] The oxygen saturation measuring device 10 according to this embodiment is provided with a power supply unit 11, which serves as a driving power source. The power supply unit 11 may be a primary battery or a secondary battery. 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 subject. The oxygen saturation measuring device of the present disclosure may be a portable type that can be worn or not, such as a portable type that can be placed close to the wrist, or a stationary type, or may be configured in any manner.

[0031] In this specification, the "direction E in which the forearm extends" overlaps with the direction in which the radius, ulna, and artery of the subject extend. Furthermore, strictly speaking, the "direction E in which the forearm extends" differs for each subject. In other words, the "direction E in which the forearm extends" is not uniquely determined by coordinates in three-dimensional space, but is individually determined based on the direction in which the radius, ulna, and artery of each subject extend.

[0032] 1, the band 12 is wrapped around the subject's wrist in the circumferential direction C of the wrist. The band 12 may be made of any material, such as resin, fabric, or metal. The band 12 is also provided with a clasp to adjust the length when wrapped around the wrist and to secure the band in place.

[0033] (Housing) The housing 14 is attached to the band 12 and comes into contact with the surface of the back of the subject's wrist (i.e., the dorsum of the hand). The housing 14 may be made of any material, such as resin or metal. The housing 14 has a constant width along the direction E in which the forearm extends. The housing 14 is provided with a PPG sensor unit 16, a display unit 18, and an arithmetic and control unit 20.

[0034] (Display Unit) As shown in Fig. 1, the display unit 18 is disposed on the surface of the housing 14 opposite the wrist. The display unit 18 is an image display device formed of, for example, a liquid crystal display. The display unit 18 displays the results of calculations performed by the calculation control unit 20 externally so that the result can be visually confirmed by the subject. The display unit 18 may be provided with a storage device for temporarily saving the results of calculations.

[0035] 2, the PPG sensor unit 16 acquires a pulse wave signal from an artery in the wrist. The measurement area 16A of the PPG sensor unit 16 is located on the side that comes into contact with the skin. Hereinafter, in this specification and drawings, the pulse wave signal will also be referred to as a "PPG signal."

[0036] As shown in FIG. 2 , the PPG sensor unit 16 of this embodiment faces, for example, an artery included in the dorsal carpal artery network on the dorsal side of the subject's wrist. The dorsal carpal artery network includes branches from the radial artery and the ulnar artery. Note that, in the present disclosure, the arteries to be measured are not limited to arteries in the wrist. In FIG. 2 , the outer edge shape of the measurement area 16A located on the skin contact side of the PPG sensor unit 16 is illustrated by a dashed line. In FIG. 2 , the contact positions of the first light-emitting element LED1, the second light-emitting element LED2, the first light-receiving element PD1, and the second light-receiving element PD2 with the skin are illustrated by dashed lines.

[0037] 2, the PPG sensor unit 16 includes a first light-emitting element LED1, a second light-emitting element LED2, and a light-receiving unit including a first light-receiving element PD1 and a second light-receiving element PD2. While the present embodiment illustrates a case in which one "PPG sensor unit" is configured with two light-emitting elements and two light-receiving elements, in the present disclosure, the number of light-emitting elements and the number of light-receiving elements that configure one PPG sensor unit are arbitrary and may be two or more. Furthermore, in the present disclosure, the number of PPG sensor units is not limited to one and may be arbitrary.

[0038] (Light-emitting element) The first light-emitting element LED1 and the second light-emitting element LED2 are both electronic components such as light-emitting diodes (LEDs). Each light-emitting element emits light by irradiating it onto the artery in the wrist. The first light-emitting element LED1 and the second light-emitting element LED2 are arranged apart from each other. In this embodiment, there is one first light-emitting element LED1 and one second light-emitting element LED2, but in the present disclosure, there may be more than one light-emitting element. The first light-emitting element LED1 and the second light-emitting element LED2 can emit red light and infrared light onto the artery. The type of light to be emitted can be selected via the calculation control unit 20.

[0039] (Light-receiving elements) The first light-receiving element PD1 and the second light-receiving element PD2 are electronic components such as photodiodes (PD). The first light-receiving element PD1 and the second light-receiving element PD2 are arranged at predetermined positions relative to the light-emitting element. In this embodiment, there is one first light-receiving element PD1 and one second light-receiving element PD2, but in the present disclosure, there may be more than one light-receiving element.

[0040] The first light receiving element PD1 receives reflected light corresponding to red light or infrared light emitted from the first light emitting element LED1 or the second light emitting element LED2. The second light receiving element PD2 receives reflected light corresponding to red light or infrared light emitted from the first light emitting element LED1 or the second light emitting element LED2. Furthermore, the first light receiving element PD1 and the second light receiving element PD2 receive reflected light corresponding to infrared light.

[0041] Although not shown, a light-shielding portion may be provided between the first light-emitting element LED1 and the second light-emitting element LED2 and the first light-receiving element PD1 and the second light-receiving element PD2. The light-shielding portion prevents the light-receiving element from directly receiving light from the light-emitting element.

[0042] An opening (not shown) may be formed in the housing 14 between the first light-emitting element LED1 and the second light-emitting element LED2 and the outside. An optical device (not shown) that is translucent to the light emitted from the light-emitting elements may be disposed in the opening. The optical device that is translucent to the emitted light is, for example, a diffusion lens that can expand the irradiation area. Although not shown, a diffusion agent may be disposed above the light-emitting elements together with or instead of the diffusion lens. Note that, in the present disclosure, an optical device that is translucent to the emitted light is not essential.

[0043] An opening (not shown) may be formed between the first light receiving element PD1 and the second light receiving element PD2 in the housing 14 and the outside. An optical device (not shown) that is translucent to light reflected from the artery in the wrist may be disposed in the opening. The optical device that is translucent to reflected light is, for example, a focusing lens that can collect reflected light. Note that, in the present disclosure, an optical device that is translucent to reflected light is not essential.

[0044] (Red Light and Infrared Light) Here, the red light and infrared light used in the oxygen saturation measurement process will be described. The oxygen saturation measurement process requires the use of a combination of two wavelength bands with different absorption coefficients for oxyhemoglobin and deoxyhemoglobin. A preferred combination of wavelength bands is the red region, which is approximately 590 nm or more and 770 nm or less, and the infrared region, which is approximately 770 nm or more and 1000 nm or less.

[0045] In particular, to measure oxygen saturation with high accuracy, it is desirable to have a large difference between the absorption coefficients of oxyhemoglobin and deoxyhemoglobin. Therefore, it is preferable that the peak wavelength of the red light be in the range of 640 nm to 660 nm, and that the peak wavelength of the infrared light be approximately 940 nm. In this embodiment, the red light and the infrared light are projected intermittently, for example, once during one arterial pulsation.

[0046] (Oxygen Saturation Measurement Principle) Next, the oxygen saturation measurement principle using two types of irradiated light and two types of reflected light will be described. Specifically, the change in amplitude of the pulse wave signal of the red reflected light is monitored over time, and the fluctuating component (AC) and the fixed component (DC) of the pulse wave signal contained in the monitored pulse wave signal are calculated. Then, the fluctuating component is divided by the fixed component (AC / DC), and the perfusion index (PI) value of the red light is calculated as PI. ＲＥＤ Similarly to the case of red light, the PI value of the reflected near-infrared light (PI) is calculated by monitoring the change in intensity of the pulse wave signal of the reflected near-infrared light over time. ＩＲ ) is calculated.

[0047] And the PI value of red light (PI ＲＥＤ ) and the PI value of near-infrared light (PI ＩＲ ) and the ratio (PI ＲＥＤ / PI ＩＲ ) is calculated. Then, the calculated ratio (PI ＲＥＤ / PI ＩＲ ) can be used in the following equation (1) to calculate the oxygen saturation: Oxygen saturation [%] = a × (PI ＲＥＤ / PI ＩＲ ) + b Equation (1) The conversion coefficients a and b in equation (1) can be determined by experiment.

[0048] (Calculation control unit) Next, an overview of the calculation control unit 20 will be described with reference to Fig. 3. As shown in Fig. 1, in this embodiment, the calculation control unit 20 is provided in the housing 14. The calculation control unit 20 is electrically connected to the first light-emitting element LED1, the second light-emitting element LED2, the first light-receiving element PD1, and the second light-receiving element PD2.

[0049] The calculation and control unit 20 measures the oxygen saturation level of the artery in the wrist illuminated with light based on the measured pulse wave signal, for example, by using a method that uses a ratio of PI values. The calculation and control unit 20 can also selectively switch between emitting light from the first light-emitting element LED1 and emitting light from the second light-emitting element LED2, depending on the relationship between a preset index value related to the measurement state and a threshold value. In the present disclosure, switching control of the light-emitting elements is not essential.

[0050] The arithmetic and control unit 20 of this embodiment corresponds to the control unit of the present disclosure. The arithmetic and control unit 20 of the pulse wave signal measuring device 30 according to this embodiment is realized integrally with the arithmetic and control unit of the oxygen saturation measuring device. In the present disclosure, the arithmetic and control unit of the pulse wave signal measuring device and the arithmetic and control unit of the oxygen saturation measuring device may be provided separately.

[0051] 3, the arithmetic and control unit 20 includes a CPU (Central Processing Unit: processor) 21, a ROM (Read Only Memory) 22, a RAM (Random Access Memory) 23, a storage 24, a user interface 25, and a communication interface 26. Each component is connected to each other via a bus 27 so as to be able to communicate with each other.

[0052] The CPU 21 is a central processing unit that executes various programs and controls each part. That is, the CPU 21 reads programs from the ROM 22 or the storage 24 and executes the programs using the RAM 23 as a work area. The CPU 21 controls the above components and performs various arithmetic processing in accordance with the programs recorded in the ROM 22 or the storage 24. The CPU 21 is a processor of the present disclosure.

[0053] In this embodiment, an oxygen saturation measurement program is stored in the ROM 22 or the storage 24. The oxygen saturation measurement program is a calculation program for measuring oxygen saturation.

[0054] The ROM 22 stores various programs and various data. The RAM 23 temporarily stores programs or data as a working area. The storage 24 is configured by an HDD (Hard Disk Drive) or an SSD (Solid State Drive) and stores various programs including the operating system and various data.

[0055] The user interface 25 is an interface through which a subject wearing the oxygen saturation measuring device 10, which is a wearable device, uses the arithmetic and control unit 20. The user interface 25 may include, for example, at least one of a liquid crystal display equipped with a touch panel that allows the subject to perform touch operations, a voice input receiving unit that receives voice input from the subject, and a button that the subject can press. The display unit of this embodiment is an example of the user interface 25.

[0056] The communication interface 26 is an interface for the arithmetic and control unit 20 to communicate with other devices, and uses standards such as Ethernet (registered trademark), FDDI, and Wi-Fi (registered trademark).

[0057] When executing the oxygen saturation measurement program or the pulse wave signal measurement program, the oxygen saturation measurement device 10 or the pulse wave signal measurement device 30 realizes various functions using the above hardware resources. The oxygen saturation measurement device 10 or the pulse wave signal measurement device 30 has, as its functional configuration, all or some of a PPG signal acquisition unit, a sensor attachment determination unit, a misalignment detection determination unit, an optical path selection unit, and a reliability determination unit. The oxygen saturation measurement device 10 also has, as its functional configuration, an oxygen saturation calculation unit. Each functional configuration is realized by the CPU 21 reading and executing the oxygen saturation measurement program or the pulse wave signal measurement program stored in the ROM 22 or the storage 24.

[0058] Next, the arithmetic and control unit 20 will be described in more detail with reference to Fig. 4. As shown in Fig. 4, the arithmetic and control unit 20 includes a measurement unit 20A, a main processor 20B, and a control PC (programmable controller) 20C.

[0059] (Measurement Unit) The measurement unit 20A of this embodiment corresponds to the first measurement unit and the second measurement unit of the present disclosure. In the present disclosure, the first measurement unit electrically connected to the first light receiving element PD1 and capable of measuring the first pulse wave signal and the second measurement unit electrically connected to the second light receiving element PD2 and capable of measuring the second pulse wave signal may be configured as different measurement units. The first pulse wave signal corresponds to the light intensity of the reflected light of red light and infrared light, respectively. The second pulse wave signal corresponds to the light intensity of the reflected light of red light and infrared light, respectively. Furthermore, the first measurement unit and the second measurement unit of the present disclosure may be configured to include the main processor 20B and the control PC 20C in FIG. 4.

[0060] The measuring unit 20A is electrically connected to each of the first light receiving element PD1 and the second light receiving element PD2. The measuring unit 20A calculates the signal strength and amplitude of the pulse wave signal of the reflected light input over time and outputs it as a waveform over time. The output data of the pulse wave signal is used to calculate the oxygen saturation level. In this specification, "measurement" includes the process of calculating the signal strength of the pulse wave signal of the reflected light.

[0061] Measurement unit 20A can measure a first pulse wave signal corresponding to the light intensity of the red light and infrared light reflected from first light receiving element PD1, and can measure a second pulse wave signal corresponding to the light intensity of the red light and infrared light reflected from second light receiving element PD2.

[0062] The pulse wave signal measured by measurement unit 20A may include pulse wave signals other than the first pulse wave signal and the second pulse wave signal of this embodiment. For example, if the first pulse wave signal and the second pulse wave signal are both pulse wave signals derived from reflected red light, measurement unit 20A may also measure a pulse wave signal derived from infrared light in addition to the pulse wave signal derived from reflected red light to measure oxygen saturation.

[0063] 4, the measurement unit 20A of this embodiment is realized by a vital sign measurement IC having an analog front-end unit, which is an analog circuit, a measurement control unit connected to the analog front-end unit, and a signal processing unit connected to the measurement control unit. The PPG sensor unit 16 is electrically connected to the analog front-end unit. The measurement control unit of the measurement unit 20A is connected to the vital sign measurement IC control unit of the main processor 20B of the arithmetic and control unit 20.

[0064] The main processor 20B includes a vital sign measurement IC control unit, a PC communication control unit connected to the vital sign measurement IC control unit, a data storage unit connected to the PC communication control unit, and a pressure sensor control unit connected to the PC communication control unit. The pressure sensor unit 17 is connected to the pressure sensor control unit.

[0065] The control PC 20C includes a measurement control unit connected to the PC communication control unit of the main processor 20B, a PC communication control unit connected to the vital sign measurement IC control unit, a data storage unit connected to the measurement control unit, and an oxygen saturation calculation unit connected to the data storage unit. As shown in Fig. 4, the PPG sensor unit 16, pressure sensor unit 17, and calculation control unit 20 are driven by connecting to a power supply unit 11 that receives power from a battery or an external power source. For example, the measurement control unit and the oxygen saturation calculation unit can be realized by a program.

[0066] The pressure sensor unit 17 can be used, for example, to determine whether the PPG sensor unit 16 is attached to the skin or not, and to detect whether the attachment position is misaligned. The pulse wave signal measured by the measurement unit 20A and the oxygen saturation level calculated by the control PC 20C can be displayed as measurement values ​​on a display or the like as the display unit 18 in response to operations by the user who is the operator.

[0067] (Arrangement of Light-Emitting and Light-Receiving Elements) Next, the arrangement of the first light-emitting element LED1, the second light-emitting element LED2, the first light-receiving element PD1, and the second light-receiving element PD2 will be specifically described with reference to FIGS.

[0068] 5A, the first light receiving element PD1 is arranged such that a first optical path L1 having a first distance is formed between it and the first light emitting element LED1. The first light receiving element PD1 is also arranged such that a second optical path L2 having a second distance different from the first distance is formed between it and the second light emitting element LED2. In FIG. 5A, the arrangement of the first light emitting element LED1, the second light emitting element LED2, the first light receiving element PD1, and the second light receiving element PD2 forms a PPG sensor unit.

[0069] In this embodiment, the second light receiving element PD2 is arranged such that a third optical path L3 having a first distance is formed between it and the first light emitting element LED1. The second light receiving element PD2 is also arranged such that a fourth optical path L4 having a second distance is formed between it and the second light emitting element LED2. In this embodiment, the first distance is longer than the second distance, and the second distance is shorter than the first distance. In the present disclosure, the relative long / short relationship may be reversed from that in this embodiment.

[0070] Therefore, the first light-emitting element LED1 is located at the vertex where two sides having the same length of the first distance intersect, the second light-emitting element LED2 is located at the vertex where two sides having the same length of the second distance intersect, and the first light-receiving element PD1 or the second light-receiving element PD2 is located at the vertex where two sides having the same length of the first distance intersect with two sides having the same length of the second distance.

[0071] In the present disclosure, it is not essential that the second optical path L2 and the fourth optical path L4 have the same second distance. The second light receiving element PD2 may be disposed in at least one of a state in which the third optical path L3 having the first distance is formed between the second light receiving element PD2 and the first light emitting element LED1, and a state in which the fourth optical path L4 having the second distance is formed between the second light emitting element LED2 and the third light receiving element PD2.

[0072] (Optical Path) In this specification, an optical path is a path of light formed between a pair of light-projecting elements and a pair of light-receiving elements where light projection and reception processing is actually performed. The optical path is determined between a preset pair of light-projecting elements and a pair of light-receiving elements. The optical path having the first distance and the optical path having the second distance of the present disclosure are not formed between a light-projecting element and a light-receiving element where light projection and reception processing is not actually performed. In this specification, unless otherwise specified, the optical path is described in a two-dimensional state in a planar view.

[0073] In addition, in the present disclosure, the distances of the multiple optical paths formed by one light-projecting element are all common, such that the first light-projecting element LED1 forms the first optical path L1 and the third optical path L3 having a common first distance. In other words, only one optical path distance is preset for one light-projecting element.

[0074] For example, even if light projected by a single light-projecting element is received by multiple light-receiving elements having different optical path distances from the single light-projecting element, the signal of reflected light (i.e., non-measured reflected light) output from the light-receiving element whose optical path has a distance other than a predetermined distance from the single light-projecting element is not subjected to measurement processing. For example, the optical signal of the non-measured reflected light is not subjected to A / D conversion. Alternatively, the light-receiving element that outputs the optical signal of the non-measured reflected light may be controlled so that the optical signal of the non-measured reflected light is selectively excluded from being output from the measurement unit to a downstream control unit. The non-measured reflected light is excluded from the reflected light that is the subject of measuring the pulse wave signal of the reflected light in the present disclosure.

[0075] (Distance of optical path) In this specification, the distance of the optical path means the distance between the centers of the light-emitting element and the light-receiving element in a planar view. If the shape of the light-emitting element and the light-receiving element is a regular polygon in a planar view, the center of the circumscribing circle of the regular polygon can be used as the center. If the shape in a planar view is not a regular polygon and therefore a circumscribing circle cannot be defined, the centroid can be used as the center.

[0076] As shown in Fig. 5B , the light emitted by the first light-emitting element LED1 and the light emitted by the second light-emitting element LED2 are selectively switched to select an optical path having either the first distance or the second distance. For example, if the subject's skin color is relatively dark, it is expected that the amount of light received during measurement will decrease. As shown on the left side of Fig. 5B , in order to suppress the decrease in the amount of light received, the second optical path L2 having the relatively shorter distance between the first distance and the second distance is selected.

[0077] Furthermore, there is a concern that if the measurement position on the subject is in a state of low perfusion, it may be difficult to obtain a clear pulse wave signal during measurement. To make it easier to obtain a clear pulse wave signal by widening the measurement range, a first optical path L1, which has the relatively longer distance between the first distance and the second distance, is selected, as shown on the right side of FIG. 5B. The optical path selection can be performed using the calculation and control unit 20. The selection of the optical path will be explained later in the pulse wave signal measurement method.

[0078] 6A , in the first modification, the arrangement pattern of the first light-emitting element LED1, the second light-emitting element LED2, the first light-receiving element PD1, and the second light-receiving element PD2 is set as the basic array BS. In the first modification, a PPG sensor unit is formed by arranging a plurality of basic arrays BS that are rectangular in plan view. In the present disclosure, the plurality of basic arrays BS is not required.

[0079] The plurality of basic arrays BS of the present disclosure are formed by one or more first light-emitting elements LED1, one or more second light-emitting elements LED2, one or more first light-receiving elements PD1, and one or more second light-receiving elements PD2. In the plurality of basic arrays BS, the first light-emitting element LED1, the second light-emitting element LED2, the first light-receiving element PD1, and the second light-receiving element PD2 are arranged so that the optical paths of adjacent basic arrays BS are formed apart without overlapping in a plan view.

[0080] 6A , in the first modified example, four light-emitting elements are arranged, each consisting of a first light-emitting element LED1, a second light-emitting element LED2, a third light-emitting element LED3, and a fourth light-emitting element LED4. Also, three light-receiving elements are arranged, each consisting of a first light-receiving element PD1, a second light-receiving element PD2, and a third light-receiving element PD3. In the first modified example, three basic arrays BS are formed. Between the three adjacent basic arrays BS, the first optical paths L1 and second optical paths L2 are formed separately without overlapping with each other.

[0081] (State in which optical paths do not overlap) In this specification, "optical paths do not overlap" means that, in a planar view, the portions other than the vertices of two optical paths that are different distances from each other do not overlap on the same straight line or do not intersect, and are separated from each other in a planar view. An optical path formed between a pair of light-projecting elements and light-receiving elements shared between adjacent basic arrays BS, such as the second optical path L2 formed between the second light-projecting element LED2 and the first light-receiving element PD1 in Fig. 6A, is not included as an overlapping optical path.

[0082] (Sharing of Elements) As shown in FIG. 6A , in the first modified example, the second light-emitting element LED2, the first light-receiving element PD1, the second light-receiving element PD2, and the third light-receiving element PD3 are shared. In the present disclosure, it is sufficient that at least one of the first light-emitting element LED1, the second light-emitting element LED2, the first light-receiving element PD1, and the second light-receiving element PD2 is shared. Also, in the present disclosure, the light-emitting elements or the light-receiving elements do not need to be shared in the basic array BS. The configuration other than the arrangement pattern of the light-emitting elements and the light-receiving elements in the first modified example is the same as in the present embodiment, and therefore a repeated description will be omitted.

[0083] 5B illustrates an example in which light emission from the first light-emitting element LED1 and light emission from the second light-emitting element LED2 are selectively switched. However, the present disclosure is not limited to this, and the switching control may also include a case in which light emission from both the first light-emitting element LED1 and the second light-emitting element LED2 is performed.

[0084] 6B , in the first modified example, three light-projection patterns are switched between: light projection from the first light-projecting element LED1; light projection from the second light-projecting element LED2; and light projection from both the first light-projecting element LED1 and the second light-projecting element LED2. This makes it possible to both suppress a decrease in the amount of received light and ensure a measurement range. As exemplarily described in the first modified example, in the present disclosure, the number of patterns for switching the light projection of each of the plurality of light-projecting elements that form optical paths with different distances is not limited to two alternatives, and can be changed as appropriate depending on the number of the plurality of light-projecting elements.

[0085] (Other Examples of Two Optical Paths) Next, other examples of the basic array BS having two optical paths as in the first modified example will be described using modified examples 2 to 7. Note that in the description of the two optical paths, unless otherwise specified, the optical path drawn with a solid line in the figure is the first optical path, and the optical path drawn with a dashed line is the second optical path. Furthermore, the configurations other than the arrangement patterns of the light-emitting elements and light-receiving elements in modified examples 2 to 7 are the same as in this embodiment, and therefore redundant description will be omitted.

[0086] 7A , in the second modification, four light-emitting elements are arranged, each consisting of a first light-emitting element LED1, a second light-emitting element LED2, a third light-emitting element LED3, and a fourth light-emitting element LED4. In addition, four light-receiving elements are arranged, each consisting of a first light-receiving element PD1, a second light-receiving element PD2, a third light-receiving element PD3, and a fourth light-receiving element PD4. In the second modification, two basic arrays BS are formed.

[0087] As shown in Figure 7B, in the second modified example, as in the first modified example, three light projections are switched between: light projection from the first light-projecting element LED1, light projection from the second light-projecting element LED2, and light projection from both the first light-projecting element LED1 and the second light-projecting element LED2.

[0088] 8A , in the third modification, four light-projecting elements are arranged, each consisting of a first light-projecting element LED1, a second light-projecting element LED2, a third light-projecting element LED3, and a fourth light-projecting element LED4. In addition, two light-receiving elements are arranged, each consisting of a first light-receiving element PD1 and a second light-receiving element PD2.

[0089] In the third modification, two basic arrays BS are formed. Between two adjacent basic arrays BS, the first optical path L1 and the second optical path L2 are formed separately without overlapping. As shown in FIG. 8A , in the third modification, the first light receiving element PD1 and the second light receiving element PD2 are shared.

[0090] 8B , in the fourth modification, six light-emitting elements are arranged, including a first light-emitting element LED1, a second light-emitting element LED2, a third light-emitting element LED3, a fourth light-emitting element LED4, a fifth light-emitting element LED5, and a sixth light-emitting element LED6. In addition, three light-receiving elements are arranged, including a first light-receiving element PD1, a second light-receiving element PD2, and a third light-receiving element PD3.

[0091] In the fourth modification, three basic arrays BS are formed. Between the three adjacent basic arrays BS, the first optical paths L1 and second optical paths L2 are formed separately without overlapping. As shown in FIG. 8B , in the fourth modification, the first light receiving element PD1, the second light receiving element PD2, and the third light receiving element PD3 are shared.

[0092] 8C , in the fifth modification, seven light-projecting elements are arranged, including a first light-projecting element LED1, a second light-projecting element LED2, a third light-projecting element LED3, a fourth light-projecting element LED4, a fifth light-projecting element LED5, a sixth light-projecting element LED6, and a seventh light-projecting element LED7. In addition, three light-receiving elements are arranged, including a first light-receiving element PD1, a second light-receiving element PD2, and a third light-receiving element PD3.

[0093] In the fifth modification, three basic arrays BS are formed. Between the three adjacent basic arrays BS, the first optical paths L1 and second optical paths L2 are formed separately without overlapping. As shown in FIG. 8C , in the fifth modification, the first light receiving element PD1, the second light receiving element PD2, and the third light receiving element PD3 are shared.

[0094] In addition, in the fifth variant, the seventh light-emitting element LED7 in the center in Figure 8C forms three optical paths having a second distance between the first light-receiving element PD1, the second light-receiving element PD2, and the third light-receiving element PD3, respectively.

[0095] In the fifth modified example, another basic array can be formed, for example, by the first light-emitting element LED1, the second light-emitting element LED2, the first light-receiving element PD1, and the second light-receiving element PD2 that form the basic array BS at the bottom left, and the seventh light-emitting element LED7 in the center. In one another basic array, four optical paths each having a common second distance are formed.

[0096] 9A , in the sixth modification, five light-emitting elements are arranged, each consisting of a first light-emitting element LED1, a second light-emitting element LED2, a third light-emitting element LED3, a fourth light-emitting element LED4, and a fifth light-emitting element LED5. In addition, four light-receiving elements are arranged, each consisting of a first light-receiving element PD1, a second light-receiving element PD2, a third light-receiving element PD3, and a fourth light-receiving element PD4. In the sixth modification, four basic arrays BS are formed.

[0097] 9A , in the sixth modification, the second light-emitting element LED2, the first light-receiving element PD1, the second light-receiving element PD2, the third light-receiving element PD3, and the fourth light-receiving element PD4 are shared.

[0098] 9B , in the seventh modification, four light-emitting elements are arranged, each consisting of a first light-emitting element LED1, a second light-emitting element LED2, a third light-emitting element LED3, and a fourth light-emitting element LED4. In addition, six light-receiving elements are arranged, each consisting of a first light-receiving element PD1, a second light-receiving element PD2, a third light-receiving element PD3, a fourth light-receiving element PD4, a fifth light-receiving element PD5, and a sixth light-receiving element PD6. In the seventh modification, four basic arrays BS are formed.

[0099] 9B , in the seventh modification, the first light-emitting element LED1, the third light-emitting element LED3, the second light-receiving element PD2, and the sixth light-receiving element PD6 are shared.

[0100] (Example of Three Optical Paths) Next, an example of a basic array BS having three optical paths, unlike the first to seventh modified examples, will be described using the eighth and ninth modified examples. In the description of the three optical paths, unless otherwise specified, the optical path drawn with a solid line in the figure is the first optical path L1, and the optical path drawn with a dashed line is the second optical path L2. Furthermore, the optical path drawn with a dashed line in the figure is the third optical path L3 having a third distance. The third distance is longer than the second distance and shorter than the first distance. The configurations of the eighth and ninth modified examples, other than the arrangement patterns of the light-emitting elements and the light-receiving elements, are the same as those of this embodiment, and therefore will not be described again.

[0101] 10A , in the eighth modification, four light-emitting elements are arranged, each consisting of a first light-emitting element LED1, a second light-emitting element LED2, a third light-emitting element LED3, and a fourth light-emitting element LED4. Also, four light-receiving elements are arranged, each consisting of a first light-receiving element PD1, a second light-receiving element PD2, a third light-receiving element PD3, and a fourth light-receiving element PD4. In the eighth modification, two basic arrays BS are formed.

[0102] Between two adjacent basic arrays BS, the first optical path L1 and the second optical path L2 are formed at a distance without overlapping. As shown in Fig. 10A, in the eighth modification, the first light-emitting element LED1 is shared. Furthermore, a third optical path L3 having a common third distance is formed between the fourth light-emitting element LED4 and the third light-receiving element PD3, and between the fourth light-emitting element LED4 and the fourth light-receiving element PD4.

[0103] 10B , in the ninth modification, seven light-emitting elements are arranged, each consisting of a first light-emitting element LED1, a second light-emitting element LED2, a third light-emitting element LED3, a fourth light-emitting element LED4, a fifth light-emitting element LED5, a sixth light-emitting element LED6, and a seventh light-emitting element LED7. In addition, three light-receiving elements are arranged, each consisting of a first light-receiving element PD1, a second light-receiving element PD2, and a third light-receiving element PD3. In the ninth modification, three basic arrays BS are formed.

[0104] Between three adjacent basic arrays BS, the first optical paths L1 and second optical paths L2 are formed at a distance without overlapping. As shown in Fig. 10B, in the ninth modification, the first light receiving element PD1, the second light receiving element PD2, and the third light receiving element PD3 are shared. Furthermore, a third optical path L3 having a common third distance is formed between the seventh light transmitting element LED7 and the first light receiving element PD1, between the seventh light transmitting element LED7 and the second light receiving element PD2, and between the seventh light transmitting element LED7 and the third light receiving element PD3.

[0105] In the ninth variant, as in the fifth variant, another basic arrangement can be formed, for example, by the first light-emitting element LED1, the second light-emitting element LED2, the first light-receiving element PD1, the second light-receiving element PD2 forming the basic arrangement BS at the bottom left, and the seventh light-emitting element LED7 in the center.

[0106] <Method for Measuring Pulse Wave Signal and Method for Measuring Oxygen Saturation> Next, a method for measuring a pulse wave signal using pulse wave signal measuring device 30 according to this embodiment will be described with reference to Fig. 11. First, first light-emitting element LED1, second light-emitting element LED2, first light-receiving element PD1, and second light-receiving element PD2 are brought into contact with the subject.

[0107] (PPG Signal Acquisition Process) Next, in step S10 in FIG. 11, the operator of pulse wave signal measuring device 30 uses arithmetic and control unit 20 to acquire PPG signals from all optical paths, i.e., both the first optical path and the second optical path.

[0108] (Process for determining whether or not the PPG sensor unit 16 is attached) Next, in step S20 in Fig. 11 , the operator uses the calculation control unit 20 to determine whether or not the PPG sensor unit 16 is attached to the skin. If it is determined that the PPG sensor unit 16 is not attached to the skin, the process of step S10 is repeated. If it is determined that the PPG sensor unit 16 is attached to the skin, the process proceeds to step S30 in Fig. 11 . In the present disclosure, the process for determining whether or not the PPG sensor unit 16 is attached to the skin in step S20 is not essential.

[0109] (Process for determining whether or not misalignment in mounting position has occurred) Next, in step S30, the operator uses the calculation and control unit 20 to determine whether or not misalignment in the mounting position of the PPG sensor unit 16 has been detected, that is, to determine whether or not misalignment has been detected. If it is determined that misalignment in the mounting position of the PPG sensor unit 16 has been detected, the process of step S10 is repeated. If it is determined that misalignment in the mounting position of the PPG sensor unit 16 has not been detected, the process proceeds to step S40 in Fig. 11. In the present disclosure, the process for determining whether or not misalignment has been detected in step S30 is not essential.

[0110] 11 , the operator switches between the light-emitting of the first light-emitting element LED1 and the light-emitting of the second light-emitting element LED2 in accordance with the relationship between the value of an index related to the measurement state and a threshold value, which is preset using the calculation control unit 20. In the present disclosure, it is not essential to switch between the light-emitting of the first light-emitting element and the light-emitting of the second light-emitting element in accordance with the relationship between the value of the index and the threshold value. For example, the switching may be performed in accordance with only the value of the index without using a threshold value.

[0111] In this embodiment, the light source can be switched to one of three patterns: only light emission from the first light-emitting element LED1, only light emission from the second light-emitting element LED2, and both light emission from the first light-emitting element LED1 and light emission from the second light-emitting element LED2. In the present disclosure, the light emission from the first light-emitting element LED1 and the light emission from the second light-emitting element LED2 are selectively switched, and an optical path having either the first distance or the second distance may be selected by the switching.

[0112] The index used in the light path selection process of this embodiment is the amount of received light. In the present disclosure, the index is not limited to the amount of received light, and may be another index such as a PI value. Specifically, first, in step S40, it is determined whether the amount of received light in the second light path L2 is equal to or less than a predetermined first threshold. If it is determined that the amount of received light in the second light path L2 is equal to or less than the first threshold, the process proceeds to step S50 in FIG. 11 .

[0113] Then, in step S50, only the light projection of the second light-projecting element LED2 that forms the second optical path L2 is executed so that the PPG signal is acquired only through the second optical path L2. That is, the second optical path L2 is selected, and only the PPG signal of the reflected light that passes through the selected second optical path L2 is measured. Then, the process proceeds to step S90 in FIG. 11 .

[0114] On the other hand, if it is determined in step S40 that the amount of light received in the second optical path L2 exceeds the first threshold, the process proceeds to step S60 in FIG. 11. Then, in step S60, it is determined whether the amount of light received in the second optical path L2 is equal to or less than a preset second threshold. The second threshold is set by an amount of light received that is greater than the first threshold. If it is determined that the amount of light received in the second optical path L2 is equal to or less than the second threshold, the process proceeds to step S70 in FIG. 11.

[0115] Then, in step S70, both the first light-emitting element LED1 forming the first optical path L1 and the second light-emitting element LED2 forming the second optical path L2 are projected so that PPG signals are acquired from both the first optical path L1 and the second optical path L2. That is, both the first optical path L1 and the second optical path L2 are selected, and PPG signals of reflected light passing through both the selected first optical path L1 and second optical path L2 are measured. Then, the process proceeds to step S90 in FIG. 11 .

[0116] Furthermore, if it is determined in step S60 that the amount of light received in the second optical path L2 exceeds the second threshold, the process proceeds to step S80 in FIG. 11 . Then, in step S80, only light projection from the first light-projecting element LED1 forming the first optical path L1 is performed so that a PPG signal is acquired only through the first optical path L1. That is, the first optical path L1 is selected, and only the PPG signal of the reflected light passing through the selected first optical path L1 is measured. Then, the process proceeds to step S90 in FIG. 11 .

[0117] (Reliability Determination Process) Next, in step S90, the operator uses the calculation and control unit 20 to determine the reliability of the PPG signal. Specifically, the attribute data of the first pulse wave signal and the second pulse wave signal, both of which are PPG signals, are compared with a reference standard. The reference standard used in the reliability determination process of this embodiment is set in advance to determine the reliability of the PPG signal. A PPG signal having attribute data that meets the reference standard is determined to have high reliability. In the present disclosure, the reliability determination process is not essential.

[0118] The attribute data and criteria in this embodiment are, for example, signal-to-noise ratios (SNRs). In the present disclosure, the attribute data is not limited to SNRs, and may be, for example, data based on intensities acquired at timings in the waveform of a PPG signal corresponding to various timings in the cardiac cycle from systole, when the ventricles contract, to diastole, when the ventricles relax. The attribute data may also be data based on the shape of the waveform of the PPG signal, such as skewness or kurtosis. Other data, such as data based on Shannon entropy as an index indicating the degree of disturbance in the PPG signal, may also be used as the attribute data.

[0119] (Oxygen saturation calculation process) Next, in step S100, the operator uses the calculation control unit 20 to select a PPG signal that has been determined to be highly reliable because it has attribute data that has been determined to meet the criteria, and calculates the oxygen saturation using the selected PPG signal.

[0120] (Another Example of Light Path Selection) While the index used in the light path selection process described with reference to FIG. 11 was the amount of received light, this disclosure is not limited to this. FIG. 12 illustrates a case in which a PI value is used as the index. The light path selection process in FIG. 12 differs from the light path selection process in FIG. 11 in that steps S40A, S50A, S60A, and S80A are executed instead of steps S40, S50, S60, and S80 in the light path selection process in FIG. 11. The following mainly describes steps S40A, S50A, S60A, and S80A in FIG. 12. Furthermore, the processes of steps other than steps S40A, S50A, S60A, and S80A are the same as the processes of the steps with the same names in FIG. 11, and therefore, redundant description will be omitted.

[0121] 12, first, in step S40A, it is determined whether the PI value of the first optical path L1 is equal to or less than a preset third threshold value. If it is determined that the PI value of the first optical path L1 is equal to or less than the third threshold value, the process proceeds to step S50A in FIG.

[0122] Then, in step S50A, only light projection from the first light-projecting element LED1 that forms the first optical path L1 is performed so that a PPG signal is acquired only through the first optical path L1. That is, the first optical path L1 is selected, and only the PPG signal of the reflected light that passes through the selected first optical path L1 is measured. Then, the process proceeds to step S90 in FIG. 12 .

[0123] On the other hand, if it is determined in step S40A that the PI value of the first optical path L1 exceeds the third threshold, the process proceeds to step S60A in Fig. 12. Then, in step S60A, it is determined whether the PI value of the first optical path L1 is equal to or less than a preset fourth threshold. The fourth threshold is set by a PI value that is greater than the third threshold.

[0124] If it is determined that the PI value of the first optical path L1 is equal to or less than the fourth threshold, the process proceeds to step S70 in Fig. 11. Then, in step S70, both the first optical path L1 and the second optical path L2 are selected, and the PPG signals of the reflected light passing through both the selected first optical path L1 and the second optical path L2 are measured, as in Fig. 11. Then, the process proceeds to step S90 in Fig. 12.

[0125] Furthermore, if it is determined in step S60A that the PI value of the first optical path L1 exceeds the fourth threshold, the process proceeds to step S80A in FIG. 12. Then, in step S80A, only light projection from the second light-projecting element LED2 that forms the second optical path L2 is performed so that a PPG signal is acquired only through the second optical path L2. That is, the second optical path L2 is selected, and only the PPG signal of the reflected light that passes through the selected second optical path L2 is measured. Then, the process proceeds to step S90 in FIG. 12.

[0126] (Still another example of optical path selection) Fig. 13 illustrates a case where both the amount of received light and the PI value are used as indices for optical path selection. The optical path selection process in Fig. 13 differs from the optical path selection process in Fig. 11 in that step S60 in the optical path selection process in Fig. 11 is replaced by step S60A similar to step S60A in Fig. 12.

[0127] That is, in the optical path selection process in Fig. 13, if it is determined in step S40 that the amount of light received in the second optical path L2 exceeds the first threshold, the process proceeds to step S60A in Fig. 11. Then, if it is determined in step S60A that the PI value of the first optical path L1 is equal to or less than the fourth threshold, the process proceeds to step S70. On the other hand, if it is determined in step S60A that the PI value of the first optical path L1 exceeds the fourth threshold, the process proceeds to step S80. The processes of the other steps are the same as the processes of the steps with the same names in Figs. 11 and 12, and therefore, repeated explanations will be omitted.

[0128] (Operation and Effect) In pulse wave signal measuring device 30 according to this embodiment, a first optical path L1 that forms a first distance and a second optical path L2 that forms a second distance different from the first distance are formed.

[0129] The inside of a subject's body is complex and uneven. For example, uneven vascular distribution, or density, occurs depending on the location and individual differences. For this reason, if only one optical path can be used to measure a pulse wave signal, even a slight shift in the measurement position, even when measuring the oxygen saturation of the same subject, can increase measurement error due to differences in subcutaneous tissue structure at each measurement position. As a result, the accuracy of oxygen saturation measurement decreases.

[0130] Furthermore, there is a trade-off between the length of the optical path formed between the light-emitting element and the light-receiving element. The shorter the optical path, the greater the amount of light received. However, the projected light has difficulty reaching deep subcutaneous tissue, resulting in a smaller measurement range. This can lead to a decrease in the measurement accuracy of the pulse wave signal, for example, in subjects with low perfusion. On the other hand, the longer the optical path, the wider the measurement range. However, the amount of light received per light-receiving element decreases. This can lead to a decrease in the measurement accuracy of the pulse wave signal, for example, in subjects with relatively dark skin, where the skin cells contain a large amount of pigment cells such as melanin. As a result, when only one optical path is used to measure the pulse wave signal, it is difficult to improve the measurement accuracy of the pulse wave signal for a variety of subjects.

[0131] Therefore, in this embodiment, in which a first optical path L1 that forms a first distance and a second optical path L2 that forms a second distance different from the first distance are formed, the measurement accuracy of the pulse wave signal can be improved compared to when an optical path having only one distance is used to measure the pulse wave signal.

[0132] In this embodiment, a first optical path L1 having a first distance is formed between the first light-emitting element LED1 and the first light-receiving element PD1, and a second optical path L2 having a second distance is formed between the second light-emitting element LED2 and the first light-receiving element PD1. Furthermore, a third optical path L3 having a first distance is formed between the first light-emitting element LED1 and the second light-receiving element PD2, and a fourth optical path L4 having a second distance is formed between the second light-emitting element LED2 and the second light-receiving element PD2.

[0133] As a result, four optical paths can be realized: the first optical path L1 and the third optical path L3, which share a common first distance, and the second optical path L2 and the fourth optical path L4, which share a common second distance. This improves the measurement accuracy of the pulse wave signal compared to when only one optical path is used to measure the pulse wave signal for one distance.

[0134] In this embodiment, pulse wave signal measuring device 30 also includes calculation control unit 20 that can switch between light emission from first light-emitting element LED1 and light emission from second light-emitting element LED2 in accordance with the value of a preset index related to the measurement state. This allows switching between light emission from first light-emitting element LED1 and light emission from second light-emitting element LED2.

[0135] Furthermore, in this embodiment, it is possible to selectively switch between emitting light from the first light-emitting element LED1 and emitting light from the second light-emitting element LED2 depending on the relationship between a preset index value related to the measurement state and a threshold value. Therefore, an optical path having either the first distance or the second distance is selected. The operation of the pulse wave signal measuring device 30 is then controlled so that only the pulse wave signal of the reflected light passing through the selected optical path is measured. This facilitates low power consumption according to the measurement state.

[0136] Furthermore, in this embodiment, the optical paths between adjacent basic arrays BS are formed apart without overlapping in a plan view, which prevents a significant decrease in overall measurement accuracy due to multiple overlapping of three-dimensional actual optical paths in a measurement region where measurement errors are likely to occur.

[0137] In this embodiment, in the basic arrangement adjacent to each other in a plan view, at least one of the first light-emitting element LED1, the second light-emitting element LED2, the first light-receiving element PD1, and the second light-receiving element PD2 is shared, which improves the efficiency of light utilization from the light source, promotes low power consumption of the pulse wave signal measuring device 30, and reduces the area of ​​the measurement region.

[0138] Furthermore, the oxygen saturation measuring device 10 according to this embodiment can calculate oxygen saturation based on the first pulse wave signal and the second pulse wave signal measured with high accuracy, thereby improving the accuracy of oxygen saturation measurement.

[0139] In this embodiment, the attribute data of the first pulse wave signal and the second pulse wave signal are compared with a predetermined standard to determine the reliability of the pulse wave signal, and the oxygen saturation level is calculated using the pulse wave signal having attribute data that meets the standard. This further improves the accuracy of oxygen saturation measurement. The pulse wave signal measuring devices according to the first to ninth modifications also have the same effects as this embodiment.

[0140] <Other Embodiments> The present disclosure has been described with reference to the above disclosed embodiments, but the descriptions and drawings forming a part of this disclosure should not be understood as limiting the present disclosure.

[0141] For example, in the present disclosure, the oxygen saturation measurement process and pulse wave signal measurement process that are executed by loading software (programs) by the CPU 21 in the above-described embodiment may be executed by various processors other than the CPU. Examples of such processors include a programmable logic device (PLD) (such as a field-programmable gate array (FPGA)) whose circuit configuration can be changed after manufacture, and a dedicated electrical circuit such as an application-specific integrated circuit (ASIC) that is a processor having a circuit configuration designed specifically for executing a specific process.

[0142] The oxygen saturation measurement process and the pulse wave signal measurement process may be performed by one of these various processors, or by a combination of two or more processors of the same or different types (e.g., a plurality of FPGAs, or a combination of a CPU and an FPGA, etc.) The hardware structure of these various processors is, more specifically, an electric circuit that combines circuit elements such as semiconductor elements.

[0143] In addition, in each of the above embodiments, the oxygen saturation measurement program and the pulse wave signal measurement program are described as being pre-stored (installed) in the ROM 22 or the storage 24, but this is not limiting. The programs may be provided in a form recorded or stored on 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. The programs may also be downloaded from an external device via a network.

[0144] The present disclosure includes various embodiments not described above, and the technical scope of the present disclosure is defined only by the invention-specific matters of the claims that are appropriate from the above explanation.

[0145] The disclosure of Japanese Patent Application No. 2024-040365, filed on March 14, 2024, is incorporated herein by reference in its entirety.

[0146] Furthermore, all publications, patent applications, and technical standards mentioned in this specification are incorporated by reference herein to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

a first light-emitting element that projects light onto an artery; a second light-emitting element that is positioned apart from the first light-emitting element and projects light onto the artery; a first light-receiving element that is positioned so that a first optical path having a first distance is formed between it and the first light-emitting element and so that a second optical path having a second distance different from the first distance is formed between it and the second light-emitting element, and that receives reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element; a first measurement unit that is electrically connected to the first light-receiving element and is capable of measuring a first pulse wave signal according to the light intensity of the reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element; and a second light-receiving element that is positioned in at least one of a state in which a third optical path having the first distance is formed between it and the first light-emitting element and a state in which a fourth optical path having the second distance is formed between it and the second light-emitting element, and that receives reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element. a second measuring unit electrically connected to the second light receiving element and capable of measuring a second pulse wave signal according to the light intensity of the reflected light corresponding to the light emitted from the first light emitting element or the second light emitting element.

2. A pulse wave signal measuring device as described in claim 1, further comprising a control unit capable of switching between the light emission of the first light-emitting element and the light emission of the second light-emitting element according to the value of a preset index relating to the measurement state.

3. The pulse wave signal measuring device according to claim 2, wherein the control unit selectively switches between emitting light from the first light-emitting element and emitting light from the second light-emitting element depending on the relationship between the value of the index and a preset threshold value related to the measurement state.

4. A pulse wave signal measuring device according to any one of claims 1 to 3, wherein, when an arrangement pattern of the first light-emitting element, the second light-emitting element, the first light-receiving element, and the second light-receiving element is set as a basic arrangement, a plurality of the basic arrangements are formed by one or more of the first light-emitting elements, one or more of the second light-emitting elements, one or more of the first light-receiving elements, and one or more of the second light-receiving elements, and the first light-emitting element, the second light-emitting element, the first light-receiving element, and the second light-receiving element are arranged so that the optical paths of adjacent basic arrangements in plan view are formed apart without overlapping.

5. A pulse wave signal measuring device according to any one of claims 1 to 4, wherein, when an arrangement pattern of the first light-emitting element, the second light-emitting element, the first light-receiving element, and the second light-receiving element is set as a basic array, a plurality of basic arrays are formed by one or more first light-emitting elements, one or more second light-emitting elements, one or more first light-receiving elements, and one or more second light-receiving elements, and at least one of the first light-emitting element, the second light-emitting element, the first light-receiving element, and the second light-receiving element is shared between basic arrays adjacent to each other in a plan view.

6. The pulse wave signal measuring device according to claim 5, wherein the second light-receiving element is arranged so that a third optical path having the first distance is formed between it and the first light-emitting element, and a fourth optical path having the second distance is formed between it and the second light-emitting element, thereby forming a plurality of quadrangular basic arrays in a planar view, wherein the first light-emitting element is located at an apex where sides having a common length of the first distance intersect, the second light-emitting element is located at an apex where sides having a common length of the second distance intersect, and the first light-receiving element or the second light-receiving element is located at an apex where an edge having the length of the first distance and an edge having the length of the second distance intersect.

7. A first light-emitting element that projects light onto an artery; a second light-emitting element that is positioned apart from the first light-emitting element and projects light onto the artery; a first light-receiving element that is positioned so that a first optical path having a first distance is formed between it and the first light-emitting element and so that a second optical path having a second distance different from the first distance is formed between it and the second light-emitting element, and that receives reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element; a first measuring unit that is electrically connected to the first light-receiving element and is capable of measuring a first pulse wave signal according to the light intensity of the reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element; and a second light-receiving element that is positioned in at least one of a state in which a third optical path having the first distance is formed between it and the first light-emitting element and a state in which a fourth optical path having the second distance is formed between it and the second light-emitting element, and that receives reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element. a control unit that can selectively switch between light projection by the first light-projecting element and light projection by the second light-projecting element; a pulse wave signal measuring device that includes: a second measuring unit electrically connected to the second light-receiving element and capable of measuring a second pulse wave signal according to the light intensity of the reflected light corresponding to the light projected from the first light-projecting element or the second light-projecting element; and a control unit that can selectively switch between light projection by the first light-projecting element and light projection by the second light-projecting element; a pulse wave signal measuring method that includes: bringing the first light-projecting element, the second light-projecting element, the first light-receiving element, and the second light-receiving element into contact with a person to be measured; selecting an optical path having one of the first distance and the second distance by selectively switching between light projection by the first light-projecting element and light projection by the second light-projecting element according to a relationship between a preset index value related to the measurement state and a threshold value; and measuring only the pulse wave signal of the reflected light that passes through the selected optical path.

8. A first light-emitting element that projects light onto an artery; a second light-emitting element that is positioned apart from the first light-emitting element and projects light onto the artery; a first light-receiving element that is positioned so that a first optical path having a first distance is formed between it and the first light-emitting element and so that a second optical path having a second distance different from the first distance is formed between it and the second light-emitting element, and that receives reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element; a first measuring unit that is electrically connected to the first light-receiving element and is capable of measuring a first pulse wave signal according to the light intensity of the reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element; and a second light-receiving element that is positioned in at least one of a state in which a third optical path having the first distance is formed between it and the first light-emitting element and a state in which a fourth optical path having the second distance is formed between it and the second light-emitting element, and that receives reflected light corresponding to the light emitted from the first light-emitting element or the second light-emitting element. an oxygen saturation measuring device comprising: a second measuring unit electrically connected to the second light receiving element and capable of measuring a second pulse wave signal according to the light intensity of the reflected light corresponding to the light emitted from the first light emitting element or the second light emitting element; and a processor electrically connected to the first measuring unit and the second measuring unit and measuring the oxygen saturation of the artery by calculating the oxygen saturation based on the first pulse wave signal and the second pulse wave signal.

9. The oxygen saturation measuring device according to claim 8, wherein the processor compares the attribute data of the first pulse wave signal and the second pulse wave signal with a predetermined standard to determine the reliability of the pulse wave signal, and calculates the oxygen saturation using the pulse wave signal having the attribute data determined to satisfy the standard.

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