Measurement device, measurement method, and program

Abstract

To accurately measure a pulse rate without additionally using a sensor for detecting a body motion signal component.SOLUTION: A measuring device for measuring a pulse rate includes a control unit for: specifying, for every waveform period, feature points of each of a first waveform and a second waveform selected from a light reception waveform of measurement light passing through a living body and a differential waveform obtained by differentiating the light reception waveform by one or more orders; assigning time stamps to feature point intervals having lengths within a prescribed range, out of a plurality of feature point intervals, the intervals between feature points of respectively adjacent waveform periods; pairing any of the feature point intervals of the first waveform to which time stamps are assigned and any of the feature point intervals of the second waveform to which time stamps are assigned according to deviations of the respective time stamps; selecting a pair from obtained pair groups based on the respective lengths of feature point intervals included in respective pairs; and calculating the pulse rate of the living body based on the feature point interval included in the selected pair.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a measurement device, a measurement method, and a program. [Background technology]

[0002] A pulse wave measurement method using photoelectric conversion is known as a method for measuring the pulse of a living body.

[0003] Patent Document 1 describes a biological condition detection device that detects pulse and body movement using at least two light-emitting elements, A light-emitting element and B light-emitting element, and one light-receiving element. Patent Document 2 discloses a pulse detection device that includes a pulse wave sensor, a body movement sensor, a pulse wave signal filtering unit, and a filter coefficient setting unit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-264302 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-172645 Summary of the Invention [Problem to be solved by the invention]

[0005] Pulse rate fluctuations are an important observation item in the treatment of chronic diseases such as heart failure. In pulse wave measurement methods using photoelectric conversion, data is collected by attaching a sensor such as a pulse wave sensor to a living subject, including a human body, and such data contains a body movement signal component generated by the influence of body movement. Since improper noise removal can lead to erroneous judgments, the body movement signal component must be removed as noise. To detect the body movement signal component, it is possible to use an additional sensor such as a body movement sensor or an acceleration sensor.

[0006] As an example, FIG. 14 shows an example of a pulse wave containing noise. The upper part of FIG. 14 is an example of a pulse wave measured, for example, by a light-receiving sensor using the PPG method. The lower part of FIG. 14 is an example of a vibration wave measured, for example, by an acceleration sensor. "PPG" is an abbreviation for photoplethysmogram. When comparing the pulse wave measured by the light-receiving sensor with the vibration wave measured by the acceleration sensor, it is found that the pulse wave is also disturbed at locations where the vibration wave is disturbed, i.e., at locations corresponding to locations where vibration is detected by the acceleration sensor. This suggests that the pulse wave itself is affected by body movement, or that the vibration of the light-receiving sensor, which is a wearable sensor, is disturbed by body movement, resulting in noise in the pulse wave measurement results. Therefore, it is necessary to exclude the data within the dashed line frame and calculate the pulse rate from the data within the solid line frame.

[0007] However, using an additional sensor other than the light receiving sensor to detect the body movement signal component leads to an increase in cost or power consumption.

[0008] An object of the present disclosure is to measure the pulse rate with high accuracy without using an additional sensor for detecting a body movement signal component. [Means for solving the problem]

[0009] A measurement device according to one aspect of the present disclosure is a measurement device for measuring a pulse rate, and includes a control unit that, when a first waveform and a second waveform are defined as two waveforms selected from a received waveform of measurement light that has passed through a living body and a differentiated waveform obtained by differentiating the received waveform by one order or more, identifies a feature point for each waveform period of the first waveform and the second waveform, assigns a timestamp to a feature point interval whose length is within a specified range among a plurality of feature point intervals that are intervals between feature points in adjacent waveform periods, pairs any of the feature point intervals assigned with a timestamp for the first waveform and any of the feature point intervals assigned with a timestamp for the second waveform according to the difference between the respective timestamps, selects pairs from the obtained group of pairs based on the respective lengths of the feature point intervals included in each pair, and calculates the pulse rate of the living body based on the feature point intervals included in the selected pair.

[0010] In one embodiment, the control unit selects a pair from the group of pairs in which a difference in length between the paired two feature points is less than a first threshold value.

[0011] In one embodiment, when timestamps assigned to a first feature point interval and a second feature point interval next to the first feature point interval among the feature point intervals to which timestamps have been assigned for the second waveform are designated as a first timestamp and a second timestamp, respectively, the control unit pairs a feature point interval to which a timestamp has been assigned for the first waveform that is later than the first timestamp and earlier than the second timestamp with the first feature point interval as a third feature point interval, and selects the pair of the first feature point interval and the third feature point interval when a difference in length between the first feature point interval and the third feature point interval is less than a first threshold value.

[0012] In one embodiment, the control unit assigns a timestamp to a feature point interval of the first waveform and the second waveform, the feature point interval having a length less than a second threshold value, among the plurality of feature point intervals.

[0013] In one embodiment, the control unit assigns a timestamp to a feature point interval of the first waveform and the second waveform, the feature point interval having a length equal to or greater than a third threshold value that is smaller than the second threshold value, among the plurality of feature point intervals.

[0014] In one embodiment, the control unit calculates the pulse rate of the living body by taking the reciprocal of the length of one of the two feature point intervals included in the selected pair.

[0015] A measurement method according to one aspect of the present disclosure is a method for measuring a pulse rate, wherein when a first waveform and a second waveform are defined as two waveforms selected from a received waveform of measurement light that has passed through a living body and a differentiated waveform obtained by differentiating the received waveform by one order or more, the method includes: identifying a feature point for each waveform period of each of the first waveform and the second waveform; assigning a timestamp to a feature point interval whose length is within a specified range among a plurality of feature point intervals that are intervals between feature points in adjacent waveform periods; pairing any of the feature point intervals assigned with a timestamp for the first waveform with any of the feature point intervals assigned with a timestamp for the second waveform according to a difference between the respective timestamps; selecting pairs from the obtained group of pairs based on the respective lengths of the feature point intervals included in each pair; and calculating the pulse rate of the living body based on the feature point intervals included in the selected pair.

[0016] A program as one aspect of the present disclosure causes a computer to execute operations for measuring a pulse rate, in which when a first waveform and a second waveform are defined as any two waveforms selected from a received waveform of measurement light that has passed through a living body and a differentiated waveform obtained by differentiating the received waveform by one order or more, the program causes a computer to execute operations including: identifying a feature point for each waveform period of the first waveform and the second waveform; assigning a timestamp to a feature point interval whose length is within a specified range among a plurality of feature point intervals that are intervals between feature points in adjacent waveform periods; pairing any of the feature point intervals assigned with a timestamp for the first waveform with any of the feature point intervals assigned with a timestamp for the second waveform according to the difference between the respective timestamps; selecting a pair from the obtained group of pairs based on the respective lengths of the feature point intervals included in each pair; and calculating the pulse rate of the living body based on the feature point intervals included in the selected pair. [Effects of the Invention]

[0017] According to the present disclosure, the pulse rate can be measured with high accuracy without using an additional sensor for detecting a body movement signal component. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a block diagram illustrating a measurement system according to an embodiment of the present disclosure. [Figure 2] FIG. 1 is a block diagram showing a configuration of a measurement device according to an embodiment of the present disclosure. [Figure 3] 10 is a flowchart illustrating the operation of a measurement device according to an embodiment of the present disclosure. [Figure 4] 3A and 3B are diagrams illustrating examples of a first waveform and a second waveform according to an embodiment of the present disclosure. [Figure 5] FIG. 10 is a diagram for explaining a procedure for extracting features of a second waveform in the embodiment of the present disclosure. [Figure 6] FIG. 10 is a diagram illustrating a feature point interval for a first waveform according to an embodiment of the present disclosure. [Figure 7]FIG. 10 is a diagram illustrating a feature point interval for a second waveform according to an embodiment of the present disclosure. [Figure 8] FIG. 4 is a diagram for explaining a procedure for removing outliers from a first waveform in the embodiment of the present disclosure. [Figure 9] FIG. 10 is a diagram for explaining a procedure for removing outliers from a second waveform in the embodiment of the present disclosure. [Figure 10] FIG. 10 is a diagram for explaining a procedure for pairing a feature point interval for a first waveform with a feature point interval for a second waveform in the embodiment of the present disclosure. [Figure 11] FIG. 10 is a diagram for explaining a procedure for pairing a feature point interval for a first waveform with a feature point interval for a second waveform in the embodiment of the present disclosure. [Figure 12] FIG. 10 is a diagram illustrating the difference between the length of the interval between feature points for the first waveform and the length of the interval between feature points for the second waveform in each pair in the embodiment of the present disclosure. [Figure 13] 10A and 10B are diagrams illustrating results of pulse rate measurements performed using a measurement device according to an embodiment of the present disclosure. [Figure 14] 10A and 10B are diagrams illustrating examples of pulse waves measured by a light receiving sensor and vibration waves measured by an acceleration sensor. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0020] In each drawing, the same or corresponding parts are denoted by the same reference numerals. In the description of this embodiment, the description of the same or corresponding parts will be omitted or simplified as appropriate.

[0021] The configuration of a measurement system 10 according to this embodiment will be described with reference to FIGS.

[0022] The measurement system 10 according to this embodiment includes a pulse rate meter 12 and a control device 30.

[0023] The pulse rate meter 12 is a device that measures the pulse rate of a living body 11, which is a subject. The pulse rate meter 12 includes a light source 13, a light receiving element 14, and a measuring device 20.

[0024] The light source 13 is, for example, an LED. "LED" is an abbreviation for light emitting diode.

[0025] The light receiving element 14 converts the intensity of light into an electrical signal. The light receiving element 14 is, for example, a photodiode.

[0026] The pulse rate meter 12 can communicate with the control device 30 directly or via a network such as a LAN or the Internet. "LAN" is an abbreviation for local area network.

[0027] The control device 30 is a computer. The control device 30 may be, for example, a dedicated device, a mobile device, a general-purpose device such as a PC, or a server device belonging to a cloud computing system or other computing system. "PC" is an abbreviation for personal computer. Mobile devices include mobile phones, smartphones, and tablets.

[0028] The configuration of the measurement device 20 according to this embodiment will be described with reference to FIG.

[0029] The measuring device 20 according to this embodiment includes a control unit 21, a storage unit 22, and a communication unit .

[0030] The control unit 21 includes at least one processor, at least one programmable circuit, at least one dedicated circuit, or any combination thereof. The processor may be a general-purpose processor such as a CPU or GPU, or a dedicated processor specialized for a specific process. "CPU" is an abbreviation for central processing unit. "GPU" is an abbreviation for graphics processing unit. An example of the programmable circuit is an FPGA. "FPGA" is an abbreviation for field-programmable gate array. An example of the dedicated circuit is an ASIC. "ASIC" is an abbreviation for application specific integrated circuit. The control unit 21 controls each part of the measurement device 20 and executes processes related to the operation of the measurement device 20.

[0031] The memory unit 22 includes at least one semiconductor memory, at least one magnetic memory, at least one optical memory, or any combination thereof. The semiconductor memory is, for example, RAM or ROM. "RAM" is an abbreviation for random access memory. "ROM" is an abbreviation for read-only memory. RAM is, for example, SRAM or DRAM. "SRAM" is an abbreviation for static random access memory. "DRAM" is an abbreviation for dynamic random access memory. ROM is, for example, EEPROM. "EEPROM" is an abbreviation for electrically erasable programmable read-only memory. The memory unit 22 functions as, for example, a main memory device, an auxiliary memory device, or a cache memory. The memory unit 22 stores data used in the operation of the measurement device 20 and data obtained by the operation of the measurement device 20. The data used in the operation of the measurement device 20 includes waveform data acquired based on the electrical signal from the light-receiving element 25. The data obtained by the operation of the measurement device 20 includes measurement data indicating the pulse rate calculated for the living body 11.

[0032] The communication unit 23 includes at least one communication interface. The communication interface is, for example, a LAN interface. The communication unit 23 receives data used in the operation of the measurement device 20 and transmits data obtained by the operation of the measurement device 20.

[0033] The functions of the measuring device 20 are realized by executing a program according to this embodiment on a processor serving as the control unit 21. That is, the functions of the measuring device 20 are realized by software. The program causes a computer to execute the operations of the measuring device 20, thereby causing the computer to function as the measuring device 20. That is, the computer functions as the measuring device 20 by executing the operations of the measuring device 20 in accordance with the program.

[0034] The program can be stored on a non-transitory computer-readable medium. Examples of non-transitory computer-readable media include flash memory, magnetic recording devices, optical disks, magneto-optical recording media, and ROMs. The program can be distributed by selling, transferring, or lending portable media such as SD cards, DVDs, or CD-ROMs that store the program. "SD" is an abbreviation for Secure Digital. "DVD" is an abbreviation for digital versatile disc. "CD-ROM" is an abbreviation for compact disc read only memory. The program can also be distributed by storing it in the storage of a server and transferring it from the server to another computer. The program can also be provided as a program product.

[0035] A computer temporarily stores a program stored on a portable medium or transferred from a server in its main storage device. The computer then reads the program stored in the main storage device using a processor and executes processing in accordance with the read program. The computer may also read the program directly from a portable medium and execute processing in accordance with the program. The computer may also execute processing in accordance with the received program each time a program is transferred from a server to the computer. Processing may also be executed through a so-called ASP-type service that achieves its functions by issuing execution instructions and obtaining results without transferring the program from the server to the computer. "ASP" is an abbreviation for application service provider. A program is information used for processing by a computer and includes something equivalent to a program. For example, data that is not a direct instruction to a computer but has properties that specify computer processing falls under the category of "something equivalent to a program."

[0036] Some or all of the functions of the measurement device 20 may be realized by a programmable circuit or a dedicated circuit as the control unit 21. In other words, some or all of the functions of the measurement device 20 may be realized by hardware.

[0037] An overview of this embodiment will be described with reference to FIG.

[0038] In the measurement system 10 according to this embodiment, the pulse of the living body 11 is measured by a measurement device 20 configured as part of a pulse rate meter 12 attached to the living body 11 as a subject. In this embodiment, the measurement device 20 measures the pulse rate using the PPG method. The PPG method uses light to read changes in the volume of blood flowing through blood vessels. For example, measurement light irradiated onto the living body 11 from a light source 13 is reflected by the living body 11, and the reflected measurement light is received by a light-receiving element 14. The measurement device 20 detects changes in the light received by the light-receiving element 14 as a pulse wave and converts the detected pulse wave into a measured value of the pulse rate. As an example, the pulse rate meter 12 is configured as a wearable device that is attached to the surface of the living body 11. For example, the pulse rate meter 12 is attached to the wrist of the human body as the living body 11.

[0039] The control unit 21 of the measurement device 20 identifies characteristic points for each waveform period of the first waveform W1 and the second waveform W2, where the first waveform W1 and the second waveform W2 are selected from the received light waveform RW of the measurement light transmitted through the living body 11 and the differentiated waveform DW obtained by differentiating the received light waveform RW by one or more orders of magnitude. In this embodiment, the differentiated waveform DW includes a first-order differentiated waveform DW1 obtained by differentiating the received light waveform RW by one order of magnitude and an nth-order differentiated waveform DWn obtained by differentiating the received light waveform RW by n orders of magnitude. n is a natural number greater than or equal to 2. In this embodiment, from the received light waveform RW and the differentiated waveforms DW1, DWn, the control unit 21 selects the received light waveform RW as the first waveform W1 and the first-order differentiated waveform DW1 as the second waveform W2. However, the first waveform W1 and the second waveform W2 are not limited to this. For example, the received light waveform RW may be selected as the first waveform W1 and the second waveform W2 may be selected as the second waveform W2. Alternatively, the first-order differential waveform DW1 may be selected as the first waveform W1, and the second-order differential waveform DW2 may be selected as the second waveform W2. The control unit 21 assigns timestamps to feature point intervals whose lengths are within a specified range among a plurality of feature point intervals, which are intervals between feature points in adjacent waveform periods, for each of the first waveform W1 and the second waveform W2. The control unit 21 pairs one of the feature point intervals assigned with a timestamp for the first waveform W1 with one of the feature point intervals assigned with a timestamp for the second waveform W2, depending on the difference between the respective timestamps, and selects pairs from the obtained group of pairs based on the respective lengths of the feature point intervals included in each pair. The control unit 21 calculates the pulse rate of the living body 11 based on the feature point intervals included in the selected pairs.

[0040] According to this embodiment, the pulse rate can be measured with high accuracy without using an additional sensor for detecting the body movement signal component.

[0041] The operation of the measurement system 10 according to this embodiment will be described with reference to Fig. 3. This operation corresponds to the measurement method according to this embodiment.

[0042] When measurement begins, the light source 13 of the pulse rate meter 12 is driven, and the light source 13 irradiates the living body 11 with measurement light. The measurement light irradiated onto the living body 11 is reflected by the living body 11. The light receiving element 14 of the pulse rate meter 12 receives the measurement light that has passed through the living body 11. The light receiving element 14 converts the intensity of the received light into an electrical signal.

[0043] In step S101, the control unit 21 of the measurement device 20 receives an electrical signal from the light-receiving element 14 and acquires a first waveform W1 based on the received electrical signal. The control unit 21 differentiates the acquired first waveform W1 to generate a differential waveform DW, which is acquired as a second waveform W2. Calculating the differential waveform DW provides information such as the peak systolic velocity and the peak diastolic velocity. FIG. 4 shows an example of the first waveform W1 and the second waveform W2 obtained by differentiating the first waveform W1 for one waveform period of the first waveform W1.

[0044] In Fig. 4, the solid line represents the first waveform W1, and the dashed line represents the second waveform W2. Point w on the second waveform W2 is the same as point w on the first waveform W1. -1 The point x on the second waveform W2 is the point obtained by differentiating the systolic velocity. -1 The point y on the second waveform W2 is the point obtained by differentiating the y on the first waveform W1. -1 The point z on the second waveform W2 is the point obtained by differentiating the point z on the first waveform W1. -1 This is the point obtained by differentiating and indicates the peak velocity during diastole.

[0045] In step S102, the control unit 21 of the measurement device 20 identifies a feature point for each waveform period of the first waveform W1 and the second waveform W2 acquired in step S101. In this embodiment, a feature point is a point that represents a feature of each period of each of the first waveform W1 and the second waveform W2. For example, a value such as a maximum value or a minimum value in each waveform period can be used as a feature. The feature is extracted by performing a predetermined feature extraction process on each of the first waveform W1 and the second waveform W2. As an example, the feature is extracted by performing the following feature extraction process.

[0046] The procedure for extracting the features of the first waveform W1 will be described. In this embodiment, the control unit 21 detects the maximum value per waveform period, i.e., the peak, as the feature of the first waveform W1. The control unit 21 estimates the pulse frequency at each time point for the first waveform W1 using a spectrogram. The control unit 21 sets the pulse width and interval from the estimated pulse frequency. The control unit 21 detects the peak using an arbitrary function with the set pulse width and interval as arguments. As the function, for example, SciPy's find_peaks can be used.

[0047] The procedure for detecting the characteristics of the second waveform W2 will be described with reference to FIG. 5. In FIG. 5, the vertical axis represents waveform amplitude, and the horizontal axis represents time. The waveform amplitude is expressed as the absolute value of the maximum displacement over one wave period. The time axis is in milliseconds. The control unit 21 of the measurement device 20 detects peaks such as w and z of the second waveform W2 by utilizing negative inflection points among the inflection points of the waveform obtained by second-order differentiation of the first waveform W1. The control unit 21 sets the width of each pulse beat in the first waveform W1 as a window width, and detects peaks such as w, which is the maximum value within each window width, for the second waveform W2, which is a waveform obtained by first-order differentiation of the first waveform W1, and extracts the detected peaks as characteristics of the second waveform W2.

[0048] The control unit 21 of the measurement device 20 identifies points corresponding to the extracted features for each of the first waveform W1 and the second waveform W2 as feature points. In this embodiment, the control unit 21 identifies points at which the waveform periods of the first waveform W1 and the second waveform W2 are maximum as feature points.

[0049] FIG. 6 shows the feature point interval for the first waveform W1. FIG. 7 shows the feature point interval for the second waveform W2. In this embodiment, the feature point interval is the interval between feature points in adjacent waveform periods. In FIGS. 6 and 7, the vertical axis represents the amplitude of the waveform, and the horizontal axis represents the time axis. The amplitude of the waveform is expressed as the absolute value of the maximum displacement during one wave period. The time axis is in seconds.

[0050] In step S103, the control unit 21 of the measurement device 20 determines whether the length of the interval between feature points in the first waveform W1 and the length of the interval between feature points in the second waveform W2 are within a specified range. A specific procedure for this determination will be described with reference to FIGS. 8 and 9. FIG. 8 plots the length of the interval between feature points in the first waveform W1 in chronological order. FIG. 9 plots the length of the interval between feature points in the second waveform W2 in chronological order. In this embodiment, a threshold is set for the standard deviation of the variation in the interval between feature points in each of the first waveform W1 and the second waveform W2 to remove outliers. In the example of FIG. 8, the upper limit of the standard deviation of the variation in the interval between feature points in the first waveform W1 is set as the second threshold, and the lower limit is set as the third threshold. That is, the third threshold is a value smaller than the second threshold. In the example of FIG. 9, the second and third thresholds are similarly set for the second waveform W2. In this embodiment, the second threshold set for the first waveform W1 and the second threshold set for the second waveform W2 are the same value, but they may be different values. Furthermore, in this embodiment, the third threshold value set for the first waveform W1 and the third threshold value set for the second waveform W2 are the same value, but they may be different values ​​as long as they are smaller than the second threshold values ​​set for the first waveform W1 and the second waveform W2, respectively.

[0051] The control unit 21 of the measurement device 20 determines whether each of the lengths of the feature point intervals in the first waveform W1 is less than the second threshold and greater than or equal to the third threshold. If the control unit 21 determines that the length of any feature point interval in the first waveform W1 is greater than or equal to the second threshold or less than the third threshold, the control unit 21 determines that the feature point interval is out of range. If the control unit 21 determines that the length of any feature point interval in the first waveform W1 is less than the second threshold and greater than or equal to the third threshold, the control unit 21 determines that the feature point interval is within range. Alternatively, the control unit 21 may determine whether each of the lengths of the feature point intervals in the first waveform W1 is less than the second threshold or greater than or equal to the third threshold. In this case, if the control unit 21 determines that the length of any feature point interval in the first waveform W1 is greater than or equal to the second threshold or less than the third threshold, the control unit 21 determines that the feature point interval is out of range. Furthermore, when the length of any feature point interval in the first waveform W1 is less than the second threshold value or equal to or greater than the third threshold value, the control unit 21 determines that the feature point interval is within the range. The control unit 21 of the measurement device 20 similarly determines the lengths of each of the multiple feature point intervals in the second waveform W2.

[0052] For feature point intervals whose lengths are determined to be outside the specified range in step S103, the process of step S104 is performed. For feature point intervals whose lengths are determined to be within the specified range in step S103, the process of step S105 is performed.

[0053] In step S104, the control unit 21 of the measurement device 20 excludes, as first outliers, feature point intervals whose lengths are determined to be outside the specified range for each of the first waveform W1 and the second waveform W2. In the examples of Fig. 8 and Fig. 9, feature point intervals that are outside the range defined by the second threshold and the third threshold are excluded as first outliers.

[0054] In step S105, the control unit 21 of the measurement device 20 assigns a timestamp to each of the first waveform W1 and the second waveform W2, the feature point intervals whose lengths are determined to be within a predetermined range. While timestamps may be assigned using any procedure, in this embodiment, the control unit 21 assigns a timestamp based on the occurrence times of the two feature points that define the feature point interval. Specifically, the control unit 21 assigns the occurrence time of one of the two feature points that define the feature point interval to which a timestamp is to be assigned as the timestamp for the feature point interval. Alternatively, the control unit 21 may assign the time between the occurrence times of the two feature points that define the feature point interval to which a timestamp is to be assigned as the timestamp for the feature point interval. For example, if a feature point interval A is defined by feature point P and feature point Q, the control unit 21 assigns the occurrence time T1 of feature point P to feature point interval A as the timestamp. Alternatively, the control unit 21 may assign the occurrence time T2 of feature point Q to feature point interval A as the timestamp. Alternatively, the control unit 21 may assign an occurrence time T3, which is a time between the occurrence time T1 and the occurrence time T2, to the feature point interval A as a time stamp.

[0055] In step S106, the control unit 21 of the measurement device 20 pairs any one of the feature point intervals to which a timestamp has been assigned for the first waveform W1 with any one of the feature point intervals to which a timestamp has been assigned for the second waveform W2, depending on the difference between the respective timestamps. The procedure for pairing any one of the feature point intervals of the first waveform W1 with any one of the feature point intervals of the second waveform W2 will be specifically described with reference to FIGS. 10 and 11.

[0056] FIG. 10 shows a time series plot of multiple feature point intervals to which timestamps were assigned in step S105. In FIG. 10, feature point intervals to which timestamps were assigned for the first waveform W1 are indicated by circles, and feature point intervals to which timestamps were assigned for the second waveform W2 are indicated by squares. In FIG. 10, the vertical axis represents the length of the feature point intervals, and the horizontal axis represents the time axis. The length of the feature point intervals is measured in milliseconds. The time axis is measured in seconds.

[0057] 10, each feature point interval assigned a timestamp for the second waveform W2 is referred to as a first feature point interval. The timestamps assigned to the first feature point interval and the second feature point interval following the first feature point interval are referred to as a first timestamp S1 and a second timestamp S2, respectively. The control unit 21 pairs a feature point interval assigned a timestamp that is later than the first timestamp S1 and earlier than the second timestamp S2 for the first waveform W1 as a third feature point interval and with the first feature point interval. As an example, among the feature point intervals assigned timestamps for the second waveform W2, the timestamp assigned to a certain feature point interval B is referred to as a first timestamp S1a, and the timestamp assigned to a feature point interval C following feature point interval B is referred to as a second timestamp S2a. When there is a feature point interval D assigned to a timestamp that is later than the first timestamp S1a and earlier than the second timestamp S2a for the first waveform W1, the control unit 21 pairs feature point interval D with feature point interval B as the corresponding feature point interval. When there are two or more feature point intervals for the first waveform W1 that are assigned time stamps that are later than the first time stamp S1a and earlier than the second time stamp S2a, the control unit 21 pairs the first of the two or more feature point intervals along the time axis as the corresponding feature point interval with feature point interval B. When any of the feature point intervals for the second waveform W2 that are assigned time stamps is set as the first feature point interval, if there is no feature point interval for the first waveform W1 that is assigned a time stamp that is later than the first time stamp S1 and earlier than the second time stamp S2, the control unit 21 does not pair the first feature point interval. A specific example of a case where there are multiple feature point intervals for the first waveform W1 that are assigned a time stamp that are later than the first time stamp S1 and earlier than the second time stamp S2 when any of the feature point intervals for the second waveform W2 that are assigned time stamps is set as the first feature point interval is when the second feature point interval is excluded as a first outlier by the processing in step S104.When any of the feature point intervals assigned with timestamps for the second waveform W2 is defined as the first feature point interval, a specific example of a case where there is no feature point interval for the first waveform W1 assigned with a timestamp after the first timestamp S1 and before the second timestamp S2 would be a case where a feature point interval that exists for the first waveform W1 after the time corresponding to the first timestamp S1 and before the time corresponding to the second timestamp S2 is excluded as a first outlier by the processing in step S104, or a case where there is no pulse within the expected window width due to arrhythmia, etc.

[0058] In this way, the control unit 21 of the measurement device 20 pairs each of the multiple feature point intervals assigned with time stamps for the first waveform W1 with one of the multiple feature point intervals assigned with time stamps for the second waveform W2. Fig. 11 shows an example of a group of pairs obtained by pairing in the example of Fig. 10. In Fig. 11, two circled points are pairs of corresponding feature point intervals.

[0059] In step S107, the control unit 21 of the measurement device 20 determines whether the difference between the lengths of the two feature point intervals paired in step S106 is less than a first threshold. Specifically, the control unit 21 determines whether the difference between the lengths of the first and third feature point intervals paired is less than the first threshold. The first threshold may be any value, for example, any value between 30 milliseconds and 50 milliseconds. The procedure for determining whether the difference is less than the first threshold will be described in detail with reference to FIG. 12. Like FIGS. 10 and 11, FIG. 12 also shows a time series plot of feature point intervals to which timestamps were assigned in step S105. In FIG. 12, feature point intervals to which timestamps were assigned for the first waveform W1 are indicated by circles, and feature point intervals to which timestamps were assigned for the second waveform W2 are indicated by squares. In FIG. 12, the vertical axis indicates the length of the feature point intervals, and the horizontal axis indicates the time axis. The length of the feature point intervals is measured in milliseconds. The time axis is measured in seconds.

[0060] The control unit 21 of the measurement device 20 compares the difference between the length of the interval between feature points of the first waveform W1 and the length of the interval between feature points of the second waveform W2 in each pair with a first threshold. In this example, among the pairs shown in FIG. 12 , the differences between the length of the interval between feature points of the first waveform W1 and the length of the interval between feature points of the second waveform W2 in the first and second pairs from the right and the first pair from the left are equal to or greater than the first threshold. The control unit 21 determines that the differences are equal to or greater than the first threshold for the first and second pairs from the right and the first pair from the left. The control unit 21 determines that the differences are less than the first threshold for pairs other than the first and second pairs from the right and the first pair from the left.

[0061] For pairs whose difference is determined to be equal to or greater than the first threshold in step S107, the process of step S108 is performed, and for pairs whose difference is determined to be less than the first threshold, the process of step S109 is performed.

[0062] In step S108, control unit 21 of measurement device 20 excludes, as second outliers, the feature point intervals included in pairs determined to have a difference equal to or greater than the first threshold, i.e., the first feature point interval and the third feature point interval. In the example of Fig. 12, the first feature point interval and the third feature point interval included in the first pair and the second pair from the right and the first pair from the left are excluded as second outliers.

[0063] In step S109, control unit 21 of measurement device 20 selects pairs for which the difference is determined to be less than the first threshold value. In the example of Fig. 12, pairs other than the first and second pairs from the right and the first pair from the left are selected.

[0064] In this way, the control unit 21 of the measuring device 20 performs the processes of steps S105 to S109, pairs any of the feature point intervals to which timestamps have been assigned for the first waveform W1 with any of the feature point intervals to which timestamps have been assigned for the second waveform W2 according to the difference between the respective timestamps, and selects pairs from the obtained group of pairs based on the lengths of the feature point intervals included in each pair.

[0065] In step S110, the control unit 21 of the measurement device 20 calculates the pulse rate of the living organism 11 based on the intervals between feature points included in the pair selected in step S109. Specifically, the control unit 21 calculates the pulse rate of the living organism 11 by taking the reciprocal of the length of one of the intervals between two feature points included in the selected pair. Alternatively, the control unit 21 may calculate the average value of the lengths of the intervals between the two feature points included in the selected pair and calculate the pulse rate of the living organism 11 by taking the reciprocal of the calculated average value. The control unit 21 stores information indicating the calculated pulse rate in the storage unit 22.

[0066] In step S111, the control unit 21 of the measuring device 20 notifies the user of the calculated pulse rate. The calculated pulse rate may be notified to the user by any procedure. For example, the control unit 21 may display the calculated pulse rate on a display serving as an output unit of the pulse rate meter 12. Alternatively, the control unit 21 may output the calculated pulse rate as audio from a speaker serving as an output unit of the pulse rate meter 12. Alternatively, the control unit 21 may transmit measurement data indicating the calculated pulse rate to the control device 30 via the communication unit 23. If the control device 30 is a server device, the control device 30 may transmit the measurement data transmitted from the measuring device 20 to a user's terminal device, such as a mobile device such as a mobile phone, smartphone, or tablet, or a PC, via a network such as a LAN or the Internet, and cause the terminal device to display the pulse rate. Alternatively, if the control device 30 is a mobile device, the control device 30 may present the pulse rate indicated by the measurement data transmitted from the measuring device 20 to the user by displaying it on a display or outputting it as audio from a speaker.

[0067] As described above, in this embodiment, the control unit 21 of the measurement device 20 identifies feature points for each waveform period of the first waveform W1 and the second waveform W2, where the first waveform W1 and the second waveform W2 are two waveforms selected from the received light waveform RW of the measurement light transmitted through the living body 11 and the differentiated waveform DW obtained by differentiating the received light waveform RW by one order or more. The control unit 21 assigns timestamps to feature point intervals between feature points in adjacent waveform periods, the lengths of which are within a specified range. The control unit 21 pairs one of the feature point intervals assigned with a timestamp for the first waveform W1 with one of the feature point intervals assigned with a timestamp for the second waveform W2, depending on the difference between the respective timestamps. The control unit 21 then selects a pair from the obtained pair group based on the length of each feature point interval included in each pair. The control unit 21 calculates the pulse rate of the living body 11 based on the feature point intervals included in the selected pair. The control unit 21 controls the notification of the calculated pulse rate to the user.

[0068] According to this embodiment, the pulse rate is calculated from the first waveform W1 and the second waveform W2 obtained by differentiating the first waveform W1. Therefore, the pulse rate can be measured accurately without using an additional sensor for detecting the body movement signal component.

[0069] FIG. 13 shows an example of actual data representing the pulse rate measurement results obtained using the measurement device 20 according to this embodiment. From top to bottom, FIG. 13 shows the first waveform W1 and the second waveform W2 according to this embodiment, the pulse rate actually calculated based on the first waveform W1 and the second waveform W2, and the vibration wave measured by the acceleration sensor. In FIG. 13, the vibration wave measured by the acceleration sensor is used to clearly indicate the location of body movement. In FIG. 13, the pulse rate actually calculated based on the first waveform W1 and the second waveform W2 is shown along with the feature point interval for the first waveform W1 and the feature point interval for the second waveform W2. In FIG. 13, the pulse rate, the feature point interval for the first waveform W1, and the feature point interval for the second waveform W2 are indicated by triangles, circles, and squares, respectively. In FIG. 13, the area enclosed by the dashed line represents the area where body movement was detected by the acceleration sensor. The area enclosed by the solid line represents the resting state where no body movement was detected. From Figure 13, it can be seen that the pulse rate in the part where the waveform is distorted due to body movement was excluded, and only the pulse rate at rest was successfully calculated.

[0070] The present disclosure is not limited to the above-described embodiments. For example, two or more blocks shown in the block diagrams may be integrated, or one block may be divided. Two or more steps shown in the flowcharts may be executed in parallel or in a different order, instead of being executed in chronological order as described, depending on the processing capabilities of the device executing each step, or as needed. Other modifications are possible within the scope of the present disclosure.

[0071] As a variation of this embodiment, instead of configuring the measuring device 20 as part of the pulse rate meter 12, the measuring device 20 may be configured as part of the control device 30. Alternatively, some of the functions of the measuring device 20 may be implemented in the pulse rate meter 12, and the remaining functions may be implemented in the control device 30. [Explanation of symbols]

[0072] 10 Measurement System 11 Living organisms 12 Pulse rate monitor 13 Light source 14 Photodetector 20 Measuring Equipment 21 Control section 22 Memory section 23 Communications Department 30 Control device

Claims

1. A measuring device for measuring pulse rate, When two of the three waveforms, namely, a received waveform of measurement light that has passed through a living body, a first-order differential waveform obtained by first-order differentiation of the received waveform, and a second-order differential waveform obtained by second-order differentiation of the received waveform, are designated as a first waveform and a second waveform, a maximum value or a minimum value is identified as a feature point for each waveform period of the first waveform and the second waveform, and a timestamp is assigned to a feature point interval whose length is within a specified range among a plurality of feature point intervals that are intervals between feature points of adjacent waveform periods; When timestamps assigned to a first feature point interval and a second feature point interval next to the first feature point interval among the feature point intervals assigned with timestamps for the second waveform are defined as a first timestamp and a second timestamp, respectively, a feature point interval assigned with a timestamp that is later than the first timestamp and earlier than the second timestamp for the first waveform is set as a third feature point interval and paired with the first feature point interval, and selecting the pair of the first feature point interval and the third feature point interval when a difference in length between the first feature point interval and the third feature point interval is less than a first threshold value; The measurement device includes a control unit that calculates the pulse rate of the living body based on the interval between feature points included in the selected pair.

2. The measurement device described in claim 1, wherein, when there are two or more feature point intervals for the first waveform that are assigned timestamps that are later than the first timestamp and earlier than the second timestamp, the control unit pairs the first feature point interval along the time axis among those two or more feature point intervals with the first feature point interval as the third feature point interval.

3. A measuring device as described in claim 1 or 2, wherein the control unit does not pair the first waveform with the first feature point interval if there is no feature point interval for the first waveform that is assigned a timestamp that is later than the first timestamp and earlier than the second timestamp.

4. 4. The measurement device according to claim 1, wherein the control unit assigns a timestamp to a feature point interval of the first waveform and the second waveform, the feature point interval having a length less than a second threshold value, among the plurality of feature point intervals.

5. 5. The measurement device according to claim 4, wherein the control unit assigns a timestamp to a feature point interval of the first waveform and the second waveform, the feature point interval having a length equal to or greater than a third threshold value that is smaller than the second threshold value, among the plurality of feature point intervals.

6. 6. The measurement device according to claim 1, wherein the control unit calculates the pulse rate of the living body by taking the reciprocal of a length of one of the two feature point intervals included in the selected pair.

7. A method for measuring a pulse rate, comprising: When the control unit determines two of three waveforms, namely, the received waveform of the measurement light that has passed through the living body, the first-order differential waveform obtained by first-order differentiation of the received waveform, and the second-order differential waveform obtained by second-order differentiation of the received waveform, as a first waveform and a second waveform, it specifies a maximum value or a minimum value as a feature point for each waveform period of the first waveform and the second waveform, and assigns a timestamp to a feature point interval whose length is within a specified range among a plurality of feature point intervals that are intervals between feature points of adjacent waveform periods; when the control unit designates timestamps assigned to a first feature point interval and a second feature point interval next to the first feature point interval among the feature point intervals assigned with timestamps for the second waveform as a first timestamp and a second timestamp, respectively, it pairs a feature point interval assigned with a timestamp that is later than the first timestamp and earlier than the second timestamp for the first waveform as a third feature point interval with the first feature point interval, and selects the pair of the first feature point interval and the third feature point interval when a difference between a length of the first feature point interval and a length of the third feature point interval is less than a first threshold value; the control unit calculates a pulse rate of the living body based on an interval between feature points included in the selected pair; , including, a measurement method.

8. An operation of measuring a pulse rate, When any two of three waveforms, namely, a received waveform of measurement light that has passed through a living body, a first-order differential waveform obtained by first-order differentiation of the received waveform, and a second-order differential waveform obtained by second-order differentiation of the received waveform, are defined as a first waveform and a second waveform, respectively, a maximum value or a minimum value is identified as a feature point for each waveform period of the first waveform and the second waveform, and a timestamp is assigned to a feature point interval whose length is within a specified range among a plurality of feature point intervals that are intervals between feature points of adjacent waveform periods; when timestamps assigned to a first feature point interval and a second feature point interval next to the first feature point interval among the feature point intervals assigned with timestamps for the second waveform are defined as a first timestamp and a second timestamp, respectively, a feature point interval assigned with a timestamp that is later than the first timestamp and earlier than the second timestamp for the first waveform is paired with the first feature point interval as a third feature point interval, and when a difference in length between the first feature point interval and the third feature point interval is less than a first threshold value, the pair of the first feature point interval and the third feature point interval is selected; calculating a pulse rate of the living body based on the intervals between feature points included in the selected pair; A program that causes a computer to perform operations including:

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