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

Abstract

To provide a pulse wave signal measuring device that has improved pulse wave signal measuring accuracy.SOLUTION: An oxygen saturation degree measuring device includes: a first light projecting element LED 1; a second light projecting element LED2; a first light receiving element PD1 arranged in a state that a first light path L1 having a first distance from the first light projecting element LED 1 is formed, and in a state that a second light path L2 having a second distance different from the first distance from the second light projecting element LED2 is formed for receiving reflection light corresponding to the light projected from the first light projecting element LED1 or the second light projecting element LED2 respectively; and a second light receiving element PD2 arranged in at least one of the state that a third light path L3 having a first distance from the first light projecting element LED1 is formed, and the state that a fourth light path L4 having a second distance from the second light projecting element LED2 for receiving reflection light corresponding to the light projected from the first light projecting element LED1 or the second light projecting element LED2 respectively.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Conventionally, oxygen saturation in arterial blood (S P As an example of a method for measuring oxygen (O2), a measurement method using absorption spectroscopy is known, as disclosed in Patent Document 1. 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 each of 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 each of the 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, Patent Document 1 discloses a pulse wave signal measuring device that includes a light-emitting element that forms multiple optical paths, including at least two optical paths, and a light-receiving element that receives reflected light from the light-emitting 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent Publication No. 10,215,698 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[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 the second aspect, the first aspect may be 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 may alternatively switch 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, a plurality of 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 the first light-emitting element, the second light-receiving element, and the first light-receiving element may be 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, a plurality of 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 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 may be shared in the basic arrays adjacent to each other in a planar view.

[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 may be 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 a fourth optical path having the second distance between it and the second light emitting element, so that, in a planar view, a plurality of the basic arrays having a quadrangular 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 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 first measuring unit that measures 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. 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 projected 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 projected from the first light-emitting element or the second light-emitting element, and a first measuring unit that is disposed so as to form a third optical path having the 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. a second light-receiving element that is positioned in at least one of the states where a fourth optical path having the second distance is formed between the first light-emitting element and the second light-emitting element, and that receives reflected light corresponding to light emitted from the first light-emitting element or the second light-emitting element, respectively; a second measurement unit that is electrically connected to the second light-receiving element and that is 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 processor that is electrically connected to the first measurement unit and the second measurement unit, and that measures oxygen saturation of the artery by calculating 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 addition, in a ninth aspect, in the eighth aspect, the processor may compare the attribute data of the first pulse wave signal and the second pulse wave signal with a preset standard to determine the reliability of the pulse wave signal, and calculate 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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a perspective view illustrating an oxygen saturation measuring device provided with a pulse wave signal measuring device according to an embodiment of the present disclosure. [Figure 2] 1 is a perspective view illustrating the state of the measurement region of a pulse wave signal when the oxygen saturation measuring device according to the present embodiment is worn on the wrist of a person being measured. FIG. [Figure 3] FIG. 2 is a block diagram comprehensively illustrating the hardware configuration of a processor of the pulse wave signal measuring device and the oxygen saturation measuring device according to the present embodiment. [Figure 4] 1 is a block diagram illustrating the hardware configuration of a processor of a pulse wave signal measuring device and an oxygen saturation measuring device according to an embodiment of the present invention based on functions. [Figure 5] Fig. 5(A) is a plan view illustrating the arrangement pattern of the light projecting element and the light receiving element of the pulse wave signal measuring device according to this embodiment, which has two optical paths. Fig. 5(B) is a plan view illustrating the drive control of the light projecting element and the light receiving element of the pulse wave signal measuring device according to this embodiment. [Figure 6] Fig. 6(A) is a plan view illustrating an arrangement pattern of a light projecting element and a light receiving element according to a first modified example, and Fig. 6(B) is a plan view illustrating drive control of the light projecting element and the light receiving element according to the first modified example having two optical paths. [Figure 7] Fig. 7(A) is a plan view illustrating an arrangement pattern of light projecting elements and light receiving elements according to a second modified example having two optical paths, and Fig. 7(B) is a plan view illustrating drive control of the light projecting elements and light receiving elements according to the second modified example. [Figure 8]Fig. 8(A) is a plan view illustrating an arrangement pattern of light projecting elements and light receiving elements according to a third modified example having two optical paths, Fig. 8(B) is a plan view illustrating an arrangement pattern of light projecting elements and light receiving elements according to a fourth modified example having two optical paths, and Fig. 8(C) is a plan view illustrating an arrangement pattern of light projecting elements and light receiving elements according to a fifth modified example having two optical paths. [Figure 9] Fig. 9(A) is a plan view illustrating an arrangement pattern of light projecting elements and light receiving elements according to a sixth modified example having two optical paths, and Fig. 9(B) is a plan view illustrating an arrangement pattern of light projecting elements and light receiving elements according to a seventh modified example having two optical paths. [Figure 10] Fig. 10(A) is a plan view illustrating an arrangement pattern of light projecting elements and light receiving elements according to an eighth modified example having three optical paths, and Fig. 10(B) is a plan view illustrating an arrangement pattern of light projecting elements and light receiving elements according to a ninth modified example having three optical paths. [Figure 11] This is a flowchart explaining a pulse wave signal measurement method using the pulse wave signal measurement device of this embodiment, and an oxygen saturation measurement method using the oxygen saturation measurement device, and explains the process of selecting an optical path using the amount of received light as an index related to the measurement state, and the process of determining the reliability of the pulse wave signal. [Figure 12] 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 another example of a pulse wave signal measurement method and an oxygen saturation measurement method. [Figure 13] 10 is a flowchart illustrating a process for selecting an optical path using both the amount of received light and the perfusion index value as indicators related to the measurement state and a process for determining the reliability of the pulse wave signal in yet another example of a pulse wave signal measurement method and an oxygen saturation measurement method. DETAILED DESCRIPTION OF THE INVENTION

[0027] Embodiments of the present disclosure will be 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 or 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 ratio of each device or component, etc., differ from the actual ones. Therefore, specific thicknesses and planar dimensions should be determined with reference to the following explanation. Furthermore, there are parts in which the dimensional relationships and ratios differ 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 is 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, for example, a portable type that can be placed close to the wrist, or may be 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 extend for each subject.

[0032] (band) As shown in Fig. 1, band 12 is wrapped around the subject's wrist in the circumferential direction C of the wrist. Band 12 may be made of any material, such as resin, fabric, or metal. Band 12 is also provided with a clasp to adjust the length when wrapped around the wrist and to secure it 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 certain 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) As shown in Fig. 1, display unit 18 is disposed on the surface of housing 14 opposite the wrist. Display unit 18 is an image display device formed of, for example, a liquid crystal display. Display unit 18 displays the results of calculations performed by calculation control unit 20 externally so that the result can be visually recognized by the subject. Display unit 18 may be provided with a storage device for temporarily storing the results of calculations.

[0035] (PPG sensor part) 2, PPG sensor unit 16 acquires a pulse wave signal from an artery in the wrist. Measurement area 16A of 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 branches from 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 has a first light-emitting element LED1, a second light-emitting element LED2, and a light-receiving unit having a first light-receiving element PD1 and a second light-receiving element PD2. In the present embodiment, an example has been given in which one "PPG sensor unit" is configured with two light-emitting elements and two light-receiving elements, but in the present disclosure, the number of light-emitting elements and the number of light-receiving elements that configure one PPG sensor unit are two or more and are arbitrary. Also, in the present disclosure, the number of PPG sensor units is not limited to one and is 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 projects 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 project red light and infrared light onto the artery. The type of light to be projected can be selected via the calculation control unit 20.

[0039] (photodetector) 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, respectively. 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, respectively. In addition, 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 elements from directly receiving light from the light-emitting elements.

[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 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 has a wavelength band ranging from approximately 590 nm to 770 nm, and the infrared region, which has a wavelength band ranging from approximately 770 nm to 1000 nm.

[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 is in the range of 640 nm to 660 nm, and the peak wavelength of the infrared light is 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, we will explain the principle of measuring oxygen saturation using two types of irradiated light and two types of reflected light. Specifically, we monitor the change in amplitude of the pulse wave signal of the reflected red light over time, and calculate the fluctuating component (AC) and the fixed component (DC) of the pulse wave signal contained in the monitored pulse wave signal. Then, by dividing the fluctuating component by the fixed component (AC / DC), the perfusion index (PI) value of the red light is calculated as PI. RED In addition, similar to the case of red light, by monitoring the change in intensity of the pulse wave signal of the reflected near-infrared light over time, the PI value of the reflected near-infrared light (PI 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 factors a and b in equation (1) can be determined experimentally.

[0048] (Calculation control unit) Next, an overview of the arithmetic control unit 20 will be described with reference to Fig. 3. As shown in Fig. 1, in this embodiment, the arithmetic control unit 20 is provided in a housing 14. The arithmetic 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 control unit 20 measures the oxygen saturation level of the artery in the wrist illuminated with light based on the measured pulse wave signal by a method using the ratio of PI values, etc. The calculation control unit 20 can also selectively switch between the light emission of the first light-emitting element LED1 and the light emission of the second light-emitting element LED2 according to the relationship between a preset index value related to the measurement state and a threshold value. In the present disclosure, the 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 of 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 each of 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 serves as a working area and temporarily stores programs or data. The storage 24 is configured with an HDD (Hard Disk Drive) or 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 the 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 section) The measurement unit 20A of this embodiment corresponds to the first measurement unit and 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 second measurement unit of the present disclosure may be configured to include the main processor 20B and control PC 20C in FIG. 4.

[0060] The measuring unit 20A is electrically connected to 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 and second pulse wave signals of this embodiment. For example, if the first and second pulse wave signals 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 control unit is connected to the pressure sensor unit 17.

[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 determine whether the attachment position is misaligned. The pulse wave signal measured by the measurement unit 20A and the oxygen saturation calculated by the control PC 20C can be displayed as measured values ​​on a display or the like as the display unit 18 in response to an operation by the user who is the operator.

[0067] (Layout of light emitting and 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] As shown in Fig. 5(A), 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. 5(A), 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 the sides having the common length of the first distance intersect. The second light-emitting element LED2 is located at the vertex where the sides having the common length of the second distance intersect. The first light-receiving element PD1 or the second light-receiving element PD2 is located at the vertex where the side having the length of the first distance intersects with the side having the 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 second light receiving element LED2.

[0072] (light 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 one light-projecting element is received by multiple light-receiving elements having different optical path distances from the light-projecting element, the signal of reflected light (i.e., non-measurement reflected light) output from the light-receiving element whose optical path has a distance other than a predetermined distance from the light-projecting element is not subjected to measurement processing. For example, the optical signal of non-measurement reflected light is not subjected to A / D conversion. Alternatively, the light-receiving element that outputs the optical signal of non-measurement reflected light may be controlled so that the optical signal of non-measurement reflected light is selectively excluded from being output from the measurement unit to a downstream control unit. The non-measurement reflected light is excluded from the reflected light that is the subject of measuring the pulse wave signal of reflected light in the present disclosure.

[0075] (optical path distance) In this specification, the distance of the optical path means the center-to-center distance between 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 a circumscribing circle cannot be defined, the centroid can be used as the center.

[0076] As shown in Fig. 5(B), 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. 5(B), 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, if the measurement position on the subject is in a state of low perfusion, there is a concern that 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, 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. 5(B). 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] (First variant: multiple basic arrays) 6A, in the first modified example, 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 a basic array BS. In the first modified example, a PPG sensor unit is formed by arranging a plurality of basic arrays BS each having a rectangular shape in a plan view. In the present disclosure, a 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 elements LED1, the second light-emitting elements LED2, the first light-receiving elements PD1, and the second light-receiving elements PD2 are arranged so that the optical paths of adjacent basic arrays BS are formed apart without overlapping in a plan view.

[0080] As shown in Fig. 6(A), 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 respective first optical paths L1 and second optical paths L2 are formed separately without overlapping.

[0081] (Light paths do not overlap) In this specification, "optical paths do not overlap" means that the portions of two optical paths that are different in distance from each other are separated from each other in a planar view without overlapping or intersecting on the same straight line, except for the vertices. An optical path formed between a pair of light-emitting elements and light-receiving elements shared between adjacent basic arrays BS, such as the second optical path L2 formed between the second light-emitting element LED2 and the first light-receiving element PD1 in Fig. 6(A), 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 this embodiment, and therefore a repeated description will be omitted.

[0083] 5(B), a case has been exemplified 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] 6(B), 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, but can be changed as appropriate depending on the number of the plurality of light-projecting elements.

[0085] (Another example 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. In the description of the two optical paths, unless otherwise specified, the optical path drawn with a solid line in the drawing is the first optical path, and the optical path drawn with a dashed line is the second optical path. In addition, 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, so redundant description will be omitted.

[0086] (Second Modification) 7(A), in the second 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, 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 modified example, two basic arrays BS are formed.

[0087] As shown in Figure 7(B), 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] (Third Modification) 8(A), in the third modified example, four light-emitting elements are arranged, which are 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, two light-receiving elements are arranged, which are a first light-receiving element PD1 and a second light-receiving element PD2.

[0089] In the third modified example, 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. 8(A), in the third modified example, the first light receiving element PD1 and the second light receiving element PD2 are shared.

[0090] (Fourth Modification) 8(B), in the fourth modified example, six light-emitting elements are arranged, which are 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. Also, three light-receiving elements are arranged, which are 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. 8(B), 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] (Fifth Modification) 8(C), in the fifth modified example, seven 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, a sixth light-emitting element LED6, and a seventh light-emitting element LED7. Also, 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. 8(C), 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 8(C) 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] (Sixth Modification) 9(A), in the sixth modified example, 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. 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 sixth modified example, four basic arrays BS are formed.

[0097] Between four adjacent basic arrays BS, the first optical paths L1 and second optical paths L2 are formed separately without overlapping with each other. As shown in Fig. 9(A) , in the sixth modified example, 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] (Seventh Modification) 9(B), 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] Between four adjacent basic arrays BS, the first optical paths L1 and second optical paths L2 are formed separately without overlapping with each other. As shown in Fig. 9(B) , 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 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] (Eighth Modification) 10(A), in the eighth 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, 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 modified example, two basic arrays BS are formed.

[0102] Between two 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. 10(A), in the eighth modification, the first light-emitting element LED1 is shared. Also, 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] (Ninth Modification) 10(B), 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. 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 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 with each other. As shown in Fig. 10(B) , 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 projecting element LED7 and the first light receiving element PD1, between the seventh light projecting element LED7 and the second light receiving element PD2, and between the seventh light projecting element LED7 and the third light receiving element PD3.

[0105] In the ninth variant, as in the fifth variant, 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 forming the basic array BS at the bottom left, and the seventh light-emitting element LED7 in the center.

[0106] <Pulse wave signal measurement method and oxygen saturation measurement method> 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 processing) 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, that is, from both the first optical path and the second optical path.

[0108] (Installation determination process) Next, in step S20 in Fig. 11, the operator uses the arithmetic and 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 of determining whether or not the PPG sensor unit 16 is attached to the skin in step S20 is not essential.

[0109] (Process to determine whether or not the mounting position is misaligned) Next, in step S30, the operator uses the arithmetic and control unit 20 to determine whether or not a misalignment in the attachment position of the PPG sensor unit 16 has been detected, that is, to determine whether or not a misalignment has been detected. If it is determined that a misalignment in the attachment position of the PPG sensor unit 16 has been detected, the process of step S10 is repeated. If it is determined that a misalignment in the attachment 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 of determining whether or not a misalignment has been detected in step S30 is not essential.

[0110] (Optical path selection process) 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-emitting element LED1 emits light only, the light-emitting element LED2 emits light only, and both the first light-emitting element LED1 and the second light-emitting element LED2 emit light. In the present disclosure, the light-emitting element LED1 emits light only and the second light-emitting element LED2 emit light only. The light-emitting element LED1 emits light only and the second light-emitting element LED2 emit light only. In addition, the light-emitting element LED1 emits light only and the second light-emitting element LED2 emit light only. In this embodiment ...

[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 first threshold value set in advance. 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 value, the process proceeds to step S50 in FIG. 11.

[0113] Then, in step S50, 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 from 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 light projection of the first light-projecting element LED1 that forms the first optical path L1 and the light projection of the second light-projecting element LED2 that forms the second optical path L2 are executed 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 the PPG signals of the reflected light that passes 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 is projected from the first light-projecting element LED1 that forms the first optical path L1 so that a PPG signal is acquired only from 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. 11.

[0117] (Reliability determination process) Next, in step S90, the operator uses the calculation 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 be highly reliable. In the present disclosure, the reliability determination process is not essential.

[0118] The attribute data and criterion in this embodiment is, for example, a signal-to-noise ratio (SNR). In the present disclosure, the attribute data is not limited to the SNR, and may be, for example, data based on the intensity 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 oxygen saturation using the selected PPG signal.

[0120] (Another example of optical path selection) While the index used in the optical 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 an example in which a PI value is used as the index. The optical path selection process in FIG. 12 differs from the optical 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 optical path selection process in FIG. 11. The following mainly describes the processing of steps S40A, S50A, S60A, and S80A in FIG. 12. Furthermore, the processing of steps other than steps S40A, S50A, S60A, and S80A is the same as the processing 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 executed so that a PPG signal is acquired only from 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 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 from 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] (Yet 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 light path selection. The light path selection process in Fig. 13 differs from the light path selection process in Fig. 11 in that step S60 in the light path selection process in Fig. 11 is replaced by step S60A similar to step S60A in Fig. 12.

[0127] 13, if it is determined in step S40 that the amount of light received by the second optical path L2 exceeds the first threshold, the process proceeds to step S60A in Fig. 11. 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 redundant explanations will be omitted.

[0128] (Action 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, unevenness in the distribution of blood vessels, or the density of blood vessels, 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 the 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 the 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 the 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 are 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 for measuring the pulse wave signal per 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 according to 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 first light-emitting element LED1 and emitting light from 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. Then, the operation of pulse wave signal measuring device 30 is 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 separately in a plan view without overlapping, 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 the oxygen saturation based on the first pulse wave signal and the second pulse wave signal measured with high accuracy, thereby improving the accuracy of measuring the oxygen saturation.

[0139] In this embodiment, the attribute data of the first pulse wave signal and the second pulse wave signal are compared with a preset 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> Although the present disclosure has been described with reference to the above disclosed embodiments, the descriptions and drawings forming a part of this disclosure should not be understood to limit 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 embodiment may be executed by various processors other than a CPU. Examples of processors in this case include programmable logic devices (PLDs) such as field-programmable gate arrays (FPGAs) whose circuit configuration can be changed after manufacture, and dedicated electrical circuits such as application-specific integrated circuits (ASICs) that are processors with circuit configurations designed specifically for executing specific processes.

[0142] The oxygen saturation measurement process and 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 (for example, multiple FPGAs, or a combination of a CPU and an FPGA, etc.) The hardware structure of these various processors is, more specifically, an electric circuit made up of a combination of circuit elements such as semiconductor elements.

[0143] In the above embodiments, the oxygen saturation measurement program and the pulse wave signal measurement program are pre-stored (installed) in ROM 22 or storage 24, but the present invention is not limited to this. The programs may be provided in a form recorded 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. [Explanation of symbols]

[0145] 10. Oxygen saturation measuring device 11 Power supply section 12 bands 14. Case 16 PPG sensor section 16A Measurement Area 17 Pressure sensor section 18 Display 20 Calculation control unit 20A Measurement unit (first measurement unit, second measurement unit) 20B main processor 20C control PC 21 processors 24 Storage 25 User Interface 26 Communication Interface 27 Bus 30 Pulse wave signal measuring device BS Basic Array C. Circumferential direction of the wrist E. Direction of extension of forearm L1 First optical path L2 second optical path L3 third light path L4 Fourth optical path LED1 First light-emitting element LED2 Second light-emitting element PD1 First photodetector PD2 Second photodetector

Claims

1. a first light-emitting element that emits light onto the artery; a second light-emitting element disposed apart from the first light-emitting element and emitting light onto the artery; a first light-receiving element that is disposed in a state where a first optical path having a first distance is formed between itself and the first light-emitting 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 itself and the second light-emitting element, and that receives reflected light corresponding to light emitted from the first light-emitting element or the second light-emitting element, a first measuring unit electrically connected to the first light receiving element and capable of measuring a first pulse wave signal corresponding to the light intensity of reflected light corresponding to light projected from the first light projecting element or the second light projecting element; a second light-receiving element that is disposed in at least one of a state where a third optical path having the first distance is formed between the first light-emitting element and the second light-emitting element, and a state where a fourth optical path having the second distance is formed between the second light-emitting element and the first light-receiving element, and that receives reflected light corresponding to 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 corresponding 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; A pulse wave signal measuring device comprising:

2. a control unit capable of switching between light emission from the first light-emitting element and light emission from the second light-emitting element in accordance with a value of a preset index relating to a measurement state; The pulse wave signal measuring device according to claim 1 .

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

4. 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 arrangement, a plurality of 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; 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 between the adjacent basic arrays in a plan view are formed apart from each other without overlapping with each other; The pulse wave signal measuring device according to any one of claims 1 to 3.

5. 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 arrangement, a plurality of 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; In the basic arrays adjacent to each other in a plan 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. The pulse wave signal measuring device according to any one of claims 1 to 3.

6. The second light receiving element is disposed in a state where a third optical path having the first distance is formed between the second light receiving element and the first light emitting element, and in a state where a fourth optical path having the second distance is formed between the second light receiving element and the first light emitting element, A plurality of the basic arrays are formed in a quadrangular shape in a plan view, the first light-emitting element is located at a vertex where two sides having the same length of the first distance intersect; the second light-emitting element is located at an apex where sides having the same length as the second distance intersect, the first light receiving element or the second light receiving element is located at an apex where a side having a length of the first distance intersects with a side having a length of the second distance; The pulse wave signal measuring device according to claim 5 .

7. a first light-emitting element that emits light onto the artery; a second light-emitting element disposed apart from the first light-emitting element and emitting light onto the artery; a first light-receiving element that is disposed in a state where a first optical path having a first distance is formed between itself and the first light-emitting 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 itself and the second light-emitting element, and that receives reflected light corresponding to light emitted from the first light-emitting element or the second light-emitting element, a first measuring unit electrically connected to the first light receiving element and capable of measuring a first pulse wave signal corresponding 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; a second light-receiving element that is disposed in at least one of a state where a third optical path having the first distance is formed between the first light-emitting element and the second light-emitting element, and a state where a fourth optical path having the second distance is formed between the second light-emitting element and the first light-receiving element, and that receives reflected light corresponding to 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 corresponding 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; a control unit capable of selectively switching between light emission from the first light-emitting element and light emission from the second light-emitting element; Using a pulse wave signal measuring device comprising: The first light-emitting element, the second light-emitting element, the first light-receiving element, and the second light-receiving element are brought into contact with the subject; selecting an optical path having one of the first distance and the second distance by selectively switching between light emission from the first light-emitting element and light emission from the second light-emitting element according to a relationship between a preset index value related to the measurement state and a threshold value; measuring only the pulse wave signal of the reflected light passing through the selected optical path; Method for measuring pulse wave signals.

8. a first light-emitting element that emits light onto the artery; a second light-emitting element disposed apart from the first light-emitting element and emitting light onto the artery; a first light-receiving element that is disposed in a state where a first optical path having a first distance is formed between itself and the first light-emitting 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 itself and the second light-emitting element, and that receives reflected light corresponding to light emitted from the first light-emitting element or the second light-emitting element, a first measuring unit electrically connected to the first light receiving element and capable of measuring a first pulse wave signal corresponding 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; a second light-receiving element that is disposed in at least one of a state where a third optical path having the first distance is formed between the first light-emitting element and the second light-emitting element, and a state where a fourth optical path having the second distance is formed between the second light-emitting element and the first light-receiving element, and that receives reflected light corresponding to 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 corresponding 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; a processor electrically connected to the first measuring unit and the second measuring unit, for calculating the oxygen saturation level based on the first pulse wave signal and the second pulse wave signal, thereby measuring the oxygen saturation level of the artery; An oxygen saturation measuring device comprising:

9. The processor: comparing the attribute data of the first pulse wave signal and the second pulse wave signal with a predetermined standard for determining the reliability of the pulse wave signals; calculating an oxygen saturation level using the pulse wave signal having the attribute data determined to satisfy the criteria; The oxygen saturation measuring device according to claim 8.

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