Heart Rate Detection System

Abstract

To provide a heartbeat interval detection system capable of calculating a heartbeat interval accurately.SOLUTION: A heartbeat interval detection system 101 includes: a sensor part 1 for detecting a plurality of heart sounds including at least one of a first heart sound and a second heart sound of a subject 100; heart sound waveform extraction parts 21 and 22 for extracting a plurality of heart sound waveforms based on the plurality of heart sounds detected by the sensor part; a selection part 28 for switching and selecting a use heart sound waveform to be used for acquiring a heartbeat interval out of the plurality of heart sound waveforms on the basis of amplitude-related information, which is the information related to a magnitude of an amplitude of the heart sound waveform; and an acquisition part 29 for acquiring the heartbeat interval calculated from the use heart sound waveform selected by the selection part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a heartbeat interval detection system. [Background technology]

[0002] Conventionally, there are known devices that use a vibration sensor to detect vibrations caused by a person's respiratory activity or heartbeat, enabling 24-hour monitoring of a person's health condition. For example, Patent Document 1 describes a biological vibration signal detection device that calculates a person's heart rate or heartbeat interval from the sound waves of heart sounds, ballistocardiograms, or pulse wave vibrations detected by a vibration sensor. From the detected heartbeat interval information, it is possible to monitor fatigue, drowsiness, stress, wakefulness, and autonomic nervous state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-75136 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in order to accurately monitor a person's health condition as described above, a high accuracy of heartbeat intervals of approximately 5 ms or less is required, but the above-mentioned device has not been able to achieve this. The present disclosure has been created in light of these circumstances, and its purpose is to provide a heartbeat interval detection system that can accurately calculate heartbeat intervals. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] According to one aspect of the present disclosure, there is provided a heartbeat interval detection system, the heartbeat interval detection system including: a first heart sound and a second heart sound of a subject; Sounda sensor unit (1) for detecting the temperature and the temperature detected by the sensor unit; a first heart sound waveform based on the first heart sound; and a second heart sound waveform based on the second heart sound detected by the sensor unit. and a cardiac sound waveform extraction unit (21, 22) for extracting the above. The first heart sound waveform and the second heart sound waveform The heart sound waveform to be used, which is the waveform used to obtain the heartbeat interval, is selected from the The first heart sound waveform and the second heart sound waveform a selection unit (28) that switches and selects based on amplitude-related information, which is information related to the magnitude of the amplitude of the heart sound waveform, and an acquisition unit (29) that acquires the heartbeat interval calculated from the used heart sound waveform selected by the selection unit.

[0007] According to this configuration, the selector switches and selects the cardiac sound waveform to be used to acquire the heartbeat interval based on amplitude-related information, which is information related to the amplitude of multiple cardiac sound waveforms. The acquirer then acquires the heartbeat interval calculated from the cardiac sound waveform to be used. Compared to acquiring the heartbeat interval by continuously using only one type of cardiac sound waveform as the cardiac sound waveform, this configuration makes it possible to appropriately select an appropriate cardiac sound waveform to be used from multiple cardiac sound waveforms, for example, as amplitude-related information, depending on the amplitude value of the cardiac sound waveform, breathing status, and other conditions. This allows the heartbeat interval to be acquired with high accuracy. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic block diagram showing a functional configuration of a heartbeat interval detection system according to a first embodiment of the present disclosure. [Figure 2] FIG. 1 is a diagram showing an electrocardiogram waveform and a cardiac sound waveform. [Figure 3] 10 is a flowchart showing a procedure of a heartbeat interval detection process executed by the heartbeat interval detection system. [Figure 4] FIG. 10 is a graph showing the deviation of the first heart sound beat interval and the second heart sound beat interval from the electrocardiogram beat interval. [Figure 5] 10 is a flowchart showing a procedure of a heartbeat interval detection process executed by a heartbeat interval detection system according to a second embodiment of the present disclosure. [Figure 6] FIG. 10 is a diagram showing a cardiac waveform after exhalation when a vibration sensor is placed on the back of a subject. [Figure 7] FIG. 10 is a diagram showing a cardiac waveform after inhalation when a vibration sensor is placed on the back of a subject. [Figure 8] FIG. 1 is a diagram showing an electrocardiogram waveform, a phonocardiogram waveform, a ballistocardiogram waveform, and a pulse waveform. [Figure 9] FIG. 10 is a diagram illustrating a learning process performed by a learning processing unit. [Figure 10] FIG. 10 is a schematic block diagram showing the functional configuration of a heartbeat interval detection system according to a third embodiment of the present disclosure. [Figure 11] 11 is a flowchart showing a procedure of a heartbeat interval detection process executed by a heartbeat interval detection system according to a third embodiment of the present disclosure. [Figure 12] 10A to 10C are diagrams illustrating the usage and concept of a heartbeat interval detection system according to a fourth embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, several embodiments will be described with reference to the drawings. A. First embodiment: A1. Heartbeat interval detection system 101 configuration: A heartbeat interval detection system 101 according to a first embodiment of the present disclosure will be described with reference to FIGS. 1 to 4. The heartbeat interval detection system 101 according to the first embodiment detects heartbeat intervals from a first heart sound and a second heart sound, which are a type of bio-vibration signal of a subject. Generally, electrocardiography is considered to be the most reliable method for measuring heartbeats. However, electrocardiography requires that electrodes be directly attached to the body surface, and the subject is constrained by cables during measurement. If the primary purpose is to measure heartbeat status for medical purposes, for example, reliability can be prioritized, and the constrained state is acceptable. However, if the system is used for a wider range of applications, such as measuring emotions and stress levels from heartbeat signals and using a driver while driving a car as the subject, the constrained state by cables is undesirable.

[0010] The heartbeat interval detection system 101 of the present disclosure detects heartbeat intervals from heart sounds in order to accurately monitor the fatigue, drowsiness, stress, alertness, autonomic nervous state, etc. of a subject while suppressing an increase in the subject's stress. The following will explain the system configuration in detail. As shown in FIG. 1, the heartbeat interval detection system 101 includes a sensor unit 1, a signal processing unit 2, and an output unit 3.

[0011] The sensor unit 1 has a single biological vibration signal detection sensor 11 (hereinafter simply referred to as "vibration sensor 11"). The vibration sensor 11 measures biological vibration signals, which are signals indicating vibrations generated from a living organism, as well as heart sounds, breathing, ballistocardiograms, pulse, etc., which can be obtained based on the biological vibration signals. The vibration sensor 11 transmits the obtained signals to the signal processing unit 2. It is preferable to use a highly sensitive vibration sensor 11 that can detect even very small signals (for example, voltages of μV) in order to detect the biological vibration signals.

[0012] The vibration sensor 11 detects cardiac sound information, including mechanical or acoustic vibrations within the heart. The mechanical or acoustic vibrations within the heart are caused by the opening and closing of heart valves or the movement of blood flowing into or out of the heart. Specifically, the vibration sensor 11 may include sensors such as an accelerometer, a microphone, or a diaphragm. The vibration sensor 11 is attached to a part of the subject, for example, near the heart, and can measure vibration signals without restraining the subject. For ease of attachment, the vibration sensor 11 preferably has an outer appearance such as a thin sheet. The vibration sensor 11 of the first embodiment corresponds to a "bicardial sound detection sensor" that detects both the first and second heart sounds with a single sensor.

[0013] The signal processing unit 2 includes a first heart sound waveform extraction unit 21, a second heart sound waveform extraction unit 22, a respiratory waveform extraction unit 23, a ballistocardiogram waveform extraction unit 24, a pulse waveform extraction unit 25, a first heart sound amplitude value acquisition unit 26, a second heart sound amplitude value acquisition unit 27, a used heart sound waveform selection unit 28, a heartbeat interval acquisition unit 29, and a learning processing unit 30. The signal processing unit 2 is comprised of a microcomputer or the like, which is comprised of a central processing unit (CPU), RAM, and ROM, and the functions of the above-mentioned units are realized by the central processing unit executing a pre-installed program. However, some or all of the functions of these units may be realized by hardware circuits.

[0014] The first heart sound waveform extraction unit 21 extracts a first heart sound waveform based on the sound wave of the first heart sound from the biological vibration signal and also detects the heartbeat timing. Heart sounds are sounds generated in conjunction with the beating of the heart and are elastic waves that propagate through gas, liquid, and solid media. Under normal conditions, heart sounds are periodic signals consisting of a first heart sound generated when the left and right atrioventricular valves close at the beginning of ventricular systole, and a second heart sound generated when the aortic valve and pulmonary valve close immediately after ventricular systole. Generally, the first heart sound is low-pitched and long, while the second heart sound is high-pitched and short. The period from the first heart sound to the second heart sound is the systole of the heart, and the period from the second heart sound to the first heart sound of the next cycle is the diastole of the heart.

[0015] As shown in the heart sound waveform in FIG. 2, the period from the first heart sound to the next first heart sound or the period from the second heart sound to the next second heart sound corresponds to the heart rate interval (HRI), and the number of first heart sounds or the number of second heart sounds per minute corresponds to the heart rate. In this embodiment, in order to distinguish between heart rate intervals based on each heart sound, the Xth heart rate interval based on the first heart sound is referred to as the "first heart rate interval HRIbx," and the Xth heart rate interval based on the second heart sound is referred to as the "second heart rate interval HRIcx." Note that heart rate intervals that do not specifically distinguish between the first heart sound and the second heart sound are also simply referred to as the "heart rate interval HRI." Furthermore, the Xth heart rate interval in the electrocardiogram waveform in FIG. 2 is referred to as the electrocardiogram heart rate interval HRIax.

[0016] The second heart sound waveform extraction unit 22 extracts a heart sound waveform based on the sound wave of the second heart sound from the biological vibration signal, and also detects the heartbeat timing. The respiratory waveform extraction unit 23 extracts a waveform indicating respiratory information from the biological vibration signal. The respiratory frequency is even lower than the frequency of the first heart sound. The cardiac ballistocardial waveform extraction unit 24 extracts a cardiac ballistocardial waveform from the biological vibration signal, and also detects the heartbeat timing.

[0017] The ballistocardial waveform is a waveform of vibration caused by the force of blood pumped by the heart. The pulse waveform extraction unit 25 extracts a pulse waveform from the biological vibration signal and also detects the heartbeat timing. The pulse waveform is a waveform caused by changes in the volume of blood vessels due to pulsating blood flow. It is preferable that each extraction unit 21, 22, 23, 24, 25 appropriately performs processing to remove noise signals. For example, after appropriately enhancing the signal strength, the signal may be passed through a filter having a passband within a predetermined frequency range.

[0018] The first heart sound amplitude value acquisition unit 26 acquires the amplitude value of the first heart sound at the heartbeat timing for each beat from the first heart sound waveform. The second heart sound amplitude value acquisition unit 27 acquires the amplitude value of the second heart sound at the heartbeat timing for each beat from the second heart sound waveform. Hereinafter, among the extracted waveforms, the amplitude value of the Xth first heart sound will be referred to as the "first heart sound amplitude value Abx," and the amplitude value of the Xth second heart sound will be referred to as the "second heart sound amplitude value Acx."

[0019] The use cardiac sound waveform selection unit 28 selects a use cardiac sound waveform, which is a waveform used to obtain heartbeat intervals, from among multiple cardiac sound waveforms, by switching between them based on amplitude-related information, which is information related to the amplitude of the cardiac sound waveform. In this embodiment, the use cardiac sound waveform selection unit 28 selects either the first cardiac sound waveform or the second cardiac sound waveform as the use cardiac sound waveform. The first cardiac sound amplitude value Abx corresponds to the "amplitude-related information." The processing procedure for selecting the use cardiac sound waveform will be described later.

[0020] The heartbeat interval acquisition unit 29 acquires the heartbeat interval calculated from the heartbeat waveform selected by the heartbeat waveform selection unit 28. In this embodiment, the heartbeat interval acquisition unit 29 calculates the heartbeat interval from the heartbeat waveform selected by the heartbeat waveform selection unit 28. Note that the heartbeat interval may be calculated before the heartbeat waveform to be used is selected. The heartbeat interval information acquired by the heartbeat interval acquisition unit 29 is output to the output unit 3. The output unit 3 stores and appropriately updates the heartbeat interval information. The output unit 3 may also be configured to include a device capable of image display and audio output, and may display the heartbeat interval information as an image or output audio when an abnormal heartbeat interval is detected. Note that because heart sounds, respiration, ballistocardiography, and pulse each have a different frequency band, all of this information can be acquired with a single vibration sensor 11.

[0021] The learning processing unit 30 performs a learning process to correct the heartbeat interval based on the phonocardiogram waveform so that it approaches the true value, using the relationships among multiple waveforms among multiple phonocardiogram waveforms, respiratory waveforms, ballistocardiogram waveforms, and pulse waveforms. The details of the learning process will be described later.

[0022] A2. Heartbeat interval detection process by the heartbeat interval detection system 101: Next, the procedure for detecting heartbeat intervals executed by the above-described heartbeat interval detection system 101 will be described. The process shown in Fig. 3 is repeatedly executed at predetermined time intervals or as appropriate in accordance with the processing in the heartbeat interval detection system 101. As shown in Fig. 3, in step 10 (hereinafter, step will be abbreviated as "S"), a vibration signal measured by the vibration sensor 11 is received by the signal processing unit 2. Next, in S20, a first heart sound waveform and a second heart sound waveform are extracted based on the vibration signal. Specifically, the first heart sound waveform extraction unit 21 extracts the first heart sound waveform, and the second heart sound waveform extraction unit 22 extracts the second heart sound waveform.

[0023] Then, in S30, the heartbeat timings of the first and second heart sound waveforms are detected. Specifically, the first heart sound waveform extraction unit 21 detects the heartbeat timing of the first heart sound, and the second heart sound waveform extraction unit 22 detects the heartbeat timing of the second heart sound.

[0024] Next, in S40, the amplitude values ​​of the first and second heart sounds are acquired. Specifically, the first heart sound amplitude value acquirer 26 acquires the first heart sound amplitude value Abx, and the second heart sound amplitude acquirer 27 acquires the second heart sound amplitude value Acx. Then, in S50, the use heart sound waveform selector 28 determines whether the first heart sound amplitude value Abx is equal to or greater than a threshold value. This determination is made for each beat.

[0025] The threshold value may be, for example, a value determined in advance by experimentation or the like as the lower limit of the subject's standard first heart sound amplitude value. Alternatively, the threshold value may be set to a certain percentage (e.g., 80%) of the maximum amplitude value obtained from the acquired first heart sound waveform, or may be set to the same value as the second heart sound amplitude value Acx that together constitutes one beat.

[0026] If the first heart sound amplitude value Abx is equal to or greater than the threshold value (S50: YES), the process proceeds to S60, where the heartbeat interval acquisition unit 29 calculates the first heart sound-to-beat interval HRIbx. On the other hand, if the first heart sound amplitude value Abx is smaller than the threshold value (S50: NO), the process proceeds to S70, where the heartbeat interval acquisition unit 29 calculates the second heart sound-to-beat interval HRIcx. After S60 and S70, in S80, the calculated heartbeat intervals HRIbx and HRIcx are output to the output unit 3. After the process of S80, this processing routine ends.

[0027] The determination process at S50 will be explained in detail using an example. As described above, the first heart sound and the second heart sound form one beat. Hereinafter, these beats will be referred to in chronological order, i.e., from left to right in FIG. 2, as the first beat, the second beat, the third beat, etc. In the example shown in FIG. 2, among the first heart sound amplitude values ​​Abx, the first heart sound amplitude value Ab3 of the third beat is smaller than the threshold value, and the other first heart sound amplitude values ​​Abx are equal to or greater than the threshold value.

[0028] In this case, the cardiac sound waveform selection unit 28 selects the first cardiac sound waveform as the cardiac sound waveform to be used for detecting the first cardiac sound interval corresponding to the interval between the first and second beats, and selects the second cardiac sound waveform as the cardiac sound waveform to be used for detecting the second cardiac sound interval corresponding to the interval between the second and third beats and the third cardiac sound interval corresponding to the interval between the third and fourth beats. Therefore, the cardiac sound intervals that are ultimately used are, in chronological order, the first cardiac sound beat interval HRIb1, the second cardiac sound beat interval HRIc2, the second cardiac sound beat interval HRIc3, the first cardiac sound beat interval HRIb4, ...

[0029] As described above, the first heart sound generally has a lower frequency intensity and a larger amplitude value than the second heart sound, so it is preferable to use the first heart sound waveform as the base for the heart sound waveform to be used. This is because a larger amplitude value reduces the risk of false detection due to a large waveform generated by electronic noise or other disturbances, compared to a smaller amplitude value. However, if the first heart sound can be detected but the detection accuracy of the first heart sound temporarily decreases due to factors such as respiratory status or other unexpected disturbances, the second heart sound waveform can be used to further improve accuracy. For this reason, in this embodiment, the heart sound waveform to be used is appropriately switched between the first heart sound and the second heart sound depending on the result of determining whether the first heart sound amplitude value Abx is equal to or greater than the threshold.

[0030] A3. Correction process for second heart sound interval HRIcx: Next, the correction process of the second cardiac sound beat interval HRIcx performed by the learning processing unit 30 will be described. In Fig. 4, the horizontal axis represents time, and the vertical axis represents the deviation ΔHRI from the electrocardiogram beat interval HRIax. In Fig. 4, the deviation ΔHRI in the first cardiac sound beat interval HRIbx is indicated by a black circle, and the deviation ΔHRI in the second cardiac sound beat interval HRIcx is indicated by a white circle. The deviations ΔHRI for the heart rate intervals HRIbx and HRIcx acquired by the heart rate acquisition unit 29 are connected by a solid line in the direction of time.

[0031] As shown in FIG. 4, the first heart sound waveform is selected as the heart sound waveform to be used from time T0 to T1 and from time T2 onward, and the second heart sound waveform is selected as the heart sound waveform to be used from time T1 to T2. The period from time T1 to T2 corresponds to a region in which the first heart sound amplitude value Abx is smaller than the threshold. The period from time T0 to T1 and from time T2 onward corresponds to a region in which the first heart sound amplitude value Abx is equal to or greater than the threshold and is sufficiently large. The learning processing unit 30 uses, for example, a well-known machine learning model to set the first heart sound beat interval HRIbx in the region in which the first heart sound amplitude value Abx is sufficiently large as the true value, and performs learning to bring the second heart sound beat interval HRIcx closer to the true value. Then, over time, the accuracy of the second heart sound beat interval HRIcx approaches the same level of accuracy as the first heart sound beat interval HRIbx.

[0032] The data corrected by learning by the learning processing unit 30 is transmitted to the heartbeat interval acquiring unit 29. When the second heart sound waveform is selected as the heart sound waveform to be used, the heartbeat interval acquiring unit 29 acquires the corrected second heart sound beat interval HRIcx. This improves the accuracy in the section in which the second heart sound beat interval HRIcx is selected.

[0033] [effect] (1) In the heartbeat interval detection system 101 of the first embodiment, the heartbeat waveform to be used is switched between the first heart sound and the second heart sound depending on whether the first heart sound amplitude value Abx is equal to or greater than a threshold. Therefore, if the first heart sound can be detected but the detection accuracy of the first heart sound temporarily decreases, the second heart sound waveform can be used to accurately calculate the heartbeat interval.

[0034] (2) Furthermore, in the heart rate detection system 101 of the first embodiment, the learning processing unit 30 can correct the second heart sound beat-to-beat interval HRIcx so that it approaches the true value more closely. This improves the detection accuracy of the second heart sound beat-to-beat interval HRIcx in the section in which the second heart sound is selected as the heart rate waveform to be used.

[0035] B. Second embodiment: Next, a heartbeat interval detection system according to a second embodiment of the present disclosure will be described with reference to Figs. 5 to 9. In the following embodiments, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. The second embodiment is similar to the first embodiment in the overall configuration of the heartbeat interval detection system 101 shown in Fig. 1, but differs from the first embodiment in part of the heartbeat interval detection processing procedure executed by the heartbeat interval detection system 101 and in the content of the learning process performed by the learning processing unit 30. These will be described in detail below.

[0036] B1. Heartbeat interval detection process by the heartbeat interval detection system: In the second embodiment, a respiratory waveform, rather than an amplitude value, is used as amplitude-related information when selecting a cardiac sound waveform to be used. The processes (S10, S20, S30) up to the detection of the heartbeat timing of each of the first and second cardiac sound waveforms are the same as those in the first embodiment. Instead of the processes of acquiring the amplitude values ​​of the first and second cardiac sounds (S40) and determining the threshold (S50) in the first embodiment, in the second embodiment, in S51 shown in FIG. 5, the cardiac sound waveform selector 28 to be used determines whether the respiratory state is between the latter half of expiration and the first half of inspiration. This determination is made for each beat. In this embodiment, the vibration sensor 11 is placed on the back of the subject.

[0037] If it is between the latter half of expiration and the first half of inspiration (S51: YES), the process proceeds to S60, where the heartbeat interval for the first heart sound, HRIbx, is calculated by the heartbeat interval acquisition unit 29. On the other hand, if it is not between the latter half of expiration and the first half of inspiration, that is, if it is between the latter half of inspiration and the first half of expiration (S51: NO), the process proceeds to S70, where the heartbeat interval acquisition unit 29 calculates the second heart sound interval, HRIcx.

[0038] Experiments conducted by the inventors have shown that when vibration sensor 11 is placed on the back of a subject, the first heart sound amplitude Abx is greater than the second heart sound amplitude Acx after exhalation, as shown in Figure 6, and the first heart sound amplitude Abx is smaller than the second heart sound amplitude Acx after inhalation, as shown in Figure 7. For this reason, the first heart sound amplitude Abx, which provides a larger amplitude value, is used from the latter half of exhalation to the first half of inspiration, which is similar to the state after exhalation, and the second heart sound amplitude Acx, which provides a larger amplitude value, is used from the latter half of inspiration to the first half of exhalation, which is similar to the state after inhalation.

[0039] That is, in the second embodiment, the cardiac sound waveform that has a larger amplitude can be selected as the cardiac sound waveform to be used based on the respiratory information acquired from the respiratory waveform, between the first and second cardiac sound waveforms. Note that the processes of S60, S70, and S80 are the same as those in the first embodiment.

[0040] B2. Learning process to improve accuracy of first and second heart sound waveforms: Next, we will explain the learning process performed by the learning processing unit 30 to improve the accuracy of the first and second cardiac sound waveforms. As shown in FIG. 8, the times at which peaks appear in the cardiac sounds, ballistocardiogram, and pulse are generally fixed for the electrocardiogram. The positions of these peaks vary depending on the placement of the vibration sensor 11. Based on the relationship between these waveforms, the heartbeat points of the cardiac sounds are corrected to be closer to their true values. Since this system does not obtain an electrocardiogram waveform, the true values ​​are determined, for example, by averaging the five extracted waveforms (first cardiac sound waveform, second cardiac sound waveform, ballistocardiogram waveform, pulse waveform, and respiratory waveform), and the peak positions of the first and second cardiac sounds are corrected based on the determined true values.

[0041] In Figure 9, the horizontal axis represents time, and the vertical axis represents the deviation ΔHRI from the electrocardiographic beat-to-beat interval HRIax. As shown in Figure 9, the deviation ΔHRI of the beat-to-beat interval calculated based on each cardiac sound waveform with the peak position corrected becomes smaller after time has passed through learning and correction, thereby improving the accuracy of obtaining the beat-to-beat interval.

[0042] C. Third embodiment: Next, a heartbeat interval detection system 103 according to a third embodiment of the present disclosure will be described with reference to FIGS. 10 and 11. As shown in FIG. 10, the sensor unit 1 included in the heartbeat interval detection system 103 according to the third embodiment has multiple (two in this embodiment) sensors. The sensor unit 1 has a first heart sound detection sensor 12 dedicated to detecting the first heart sound and a second heart sound detection sensor 13 dedicated to detecting the second heart sound. The first heart sound waveform extraction unit 21 extracts a heart sound waveform based on the sound wave of the first heart sound from the biological vibration signal detected by the first heart sound detection sensor 12, and also detects the heartbeat timing. The second heart sound waveform extraction unit 22 extracts a heart sound waveform based on the sound wave of the second heart sound from the biological vibration signal detected by the second heart sound detection sensor 13, and also detects the heartbeat timing.

[0043] Based on the above-described principle of how the first heart sound is generated, the first heart sound detection sensor 12 can be placed in a location where the first heart sound is more likely to be received strongly, for example, the lower part of the chest area on the abdominal side of the subject. Similarly, based on the above-described principle of how the second heart sound is generated, the second heart sound detection sensor 13 can be placed in a location where the second heart sound is more likely to be received strongly, for example, the upper part of the chest area on the back of the subject. Note that this sensor placement is just one example, and the location where the heart sound is more likely to be received strongly varies depending on the subject, so it can be changed as appropriate.

[0044] 11 , in the third embodiment, each heart sound is received by a dedicated sensor 12, 13. In S11, the vibration signal measured by the first heart sound detection sensor 12 is received by the signal processing unit 2. Next, in S21, the first heart sound waveform extraction unit 21 extracts a first heart sound waveform based on the received vibration signal. Then, in S31, the heartbeat timing of the first heart sound waveform is detected. Next, in S41, the first heart sound amplitude value Abx is acquired by the first heart sound amplitude value acquisition unit 26.

[0045] For the second heart sound, the second heart sound detection sensor 13 acquires a second heart sound amplitude value Acx through processing (S12, S22, S32, S42) similar to the processing (S11, S21, S31, S41) up to the acquisition of the first heart sound amplitude value Abx by the first heart sound detection sensor 12. In the flowchart of Fig. 11, the processing from signal reception by the first heart sound detection sensor 12 to acquisition of the first heart sound amplitude value Abx (S11, S21, S31, S41) and the processing from signal reception by the second heart sound detection sensor 13 to acquisition of the second heart sound amplitude value Acx (S12, S22, S32, S42) are shown branched for convenience, but these series of processing steps may be executed simultaneously or sequentially. The processing steps at S50, S60, S70, and S80 are the same as those in the first embodiment.

[0046] According to the heartbeat interval detection system 103 of the third embodiment, the first heart sound is detected by the first heart sound detection sensor 12, and the second heart sound is detected by the second heart sound detection sensor 13. Therefore, depending on the arrangement of the sensors 12 and 13, the waveforms of either heart sound can be detected as large, strong signals, allowing for larger amplitude values. This improves the accuracy of detecting each heart sound. Accordingly, even if the amplitude value temporarily decreases, it may be possible to continue using the first heart sound waveform as the heart sound waveform to be used. Furthermore, even when the second heart sound waveform is used as the heart sound waveform to be used, its large amplitude value improves detection accuracy. This in turn improves the accuracy of acquiring heartbeat intervals by the heartbeat interval acquisition unit 29.

[0047] D. Fourth embodiment: Next, a heartbeat interval detection system according to a fourth embodiment of the present disclosure will be described with reference to Fig. 12. The sensor unit 1 included in the heartbeat interval detection system of the fourth embodiment has a plurality of sensors, similar to the third embodiment. Although a system configuration diagram is omitted, the fourth embodiment has a first bi-heart sound detection sensor 14 instead of the first heart sound detection sensor 12 in the third embodiment, and a second bi-heart sound detection sensor 15 instead of the second heart sound detection sensor 13 in the third embodiment.

[0048] The fourth embodiment differs from the third embodiment in that the first heart sound detection sensor 14 and the second heart sound detection sensor 15 detect both the first and second heart sounds, respectively. The first heart sound detection sensor 14 and the second heart sound detection sensor 15 detect heart sound waveforms whose amplitude fluctuations have opposite characteristics. To detect the opposite characteristics, for example, the first heart sound detection sensor 14 is placed on the ventral side of the subject 100, and the second heart sound detection sensor 15 is placed on the dorsal side of the subject 100, as shown in FIG.

[0049] Here, amplitude fluctuation refers to the periodic fluctuation over time of the amplitude intensity of the heart sound, and can be represented as a waveform that connects the heart sound amplitude values ​​in a time series when the heart sound occurs, as shown on the right side of Figure 12. Also, the inverse characteristic refers to a characteristic in which the peaks appear at different times in the amplitude fluctuation, resulting in the peaks and valleys of the amplitude fluctuation waveform being reversed.

[0050] In the fourth embodiment, similarly to the above embodiments, an optimal waveform is selected as the cardiac sound waveform to be used from a plurality of cardiac sound waveforms. In this embodiment, a total of four waveforms are obtained: a first cardiac sound waveform and a second cardiac sound waveform detected by the first cardiac sound detection sensor 14, and a first cardiac sound waveform and a second cardiac sound waveform detected by the second cardiac sound detection sensor 15. Of these waveforms, the waveform with the largest amplitude in the time series can be preferentially selected as the cardiac sound waveform to calculate the heartbeat interval.

[0051] Alternatively, for example, the first heart sound waveform detected by the first heart sound detection sensor 14 may be used as the base heart sound waveform, and as in the first embodiment, if the amplitude value of the first heart sound waveform detected by the first heart sound detection sensor 14 is smaller than the threshold value, the first heart sound waveform detected by the second heart sound detection sensor 15 may be selected as the heart sound waveform to be used.

[0052] Furthermore, in addition to the respiratory information, a cardiac sound waveform with a larger amplitude value may be selected as the cardiac sound waveform to be used. For example, if the respiratory state is determined to be between the latter half of inspiration and the first half of expiration, the second cardiac sound waveform detected by the second cardiac sound detection sensor 15 on the back side may be selected as the cardiac sound waveform to be used.

[0053] As described above, the heartbeat interval calculation system of the fourth embodiment can obtain multiple heart sound waveforms with opposite characteristics for the first and second heart sounds, increasing the number of waveform combinations that can be selected as the heart sound waveform to be used, making it possible to select the optimal heart sound waveform as appropriate depending on the situation.

[0054] E. Other Embodiments: (E1) In the first embodiment, the threshold value of the amplitude value may be changed as appropriate when data is accumulated over time. For example, the threshold value may be set to an arbitrary constant value at the beginning of measurement, and once data is accumulated, the threshold value may be changed to 80% of the maximum amplitude value up to that point.

[0055] (E2) In the third and fourth embodiments, the sensor unit 1 may be configured to include three or more sensors.

[0056] (E3) In the third embodiment, the cardiac sound waveform to be used may be selected based on the respiratory state. In this case, the process of S51 in the flowchart shown in Fig. 5 may be executed instead of the processes of S41, S42, and S50 in the flowchart shown in Fig. 11.

[0057] (E4) The first and second embodiments may be combined to combine a determination based on a threshold value of the amplitude value with a determination based on respiratory information. For example, after the threshold determination, the respiratory information may be taken into account to finally determine the cardiac sound waveform to be used.

[0058] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in each embodiment corresponding to the technical features in the form described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0059] 1...sensor unit, 2...signal processing unit, 3...output unit, 11...biological vibration signal detection sensor (both heart sound detection sensor), 12...first heart sound detection sensor, 13...second heart sound detection sensor, 14...first both heart sound detection sensor, 15...second both heart sound detection sensor, 21...first heart sound waveform extraction unit, 22...second heart sound waveform extraction unit, 23...respiratory waveform extraction unit, 24...cardiac ballistocardial waveform extraction unit, 25...pulse waveform extraction unit, 26...first heart sound amplitude value acquisition unit, 27...second heart sound amplitude value acquisition unit, 28...used heart sound waveform selection unit, 29...heart beat interval acquisition unit, 30...learning processing unit, 100...subject, 101, 103...heart beat interval detection system

Claims

1. A sensor unit (1) for detecting a first heart sound and a second heart sound of a subject (100); a heart sound waveform extraction unit (21, 22) for extracting a first heart sound waveform based on the first heart sound detected by the sensor unit and a second heart sound waveform based on the second heart sound detected by the sensor unit; a selection unit (28) that selects a use heart sound waveform, which is a waveform to be used for obtaining a heart beat interval, from the first heart sound waveform and the second heart sound waveform, based on amplitude related information, which is information related to the magnitude of the amplitude of the first heart sound waveform and the second heart sound waveform; an acquisition unit (29) that acquires the heartbeat interval calculated from the used heart sound waveform selected by the selection unit; A heart rate detection system comprising:

2. The sensor unit has a bi-heart sound detection sensor (11) for detecting the first heart sound and the second heart sound, the amplitude-related information includes an amplitude value of the first heart sound waveform; The selection unit selects, as the used heart sound waveform, 2. The heart beat interval detection system of claim 1, wherein the first heart sound waveform is selected when the amplitude value of the first heart sound is equal to or greater than a threshold, and the second heart sound waveform is selected when the amplitude value of the first heart sound is less than the threshold.

3. The heartbeat detection system according to claim 2 , wherein the threshold value is set to the same value as an amplitude value of the second heart sound that forms the same beat as the first heart sound.

4. the sensor unit includes a first heart sound detection sensor (12) for detecting the first heart sound, and a second heart sound detection sensor (13) provided separately from the first heart sound detection sensor for detecting the second heart sound, 2. The heart beat interval detection system according to claim 1, wherein the heart sound waveform extraction unit extracts the first heart sound waveform based on the first heart sound detected by the first heart sound detection sensor, and the second heart sound waveform based on the second heart sound detected by the second heart sound detection sensor.

5. A sensor unit (1) for detecting a plurality of heart sounds including at least one of a first heart sound and a second heart sound of a subject (100); a cardiac sound waveform extraction unit (21, 22) that extracts a plurality of cardiac sound waveforms based on the plurality of cardiac sounds detected by the sensor unit; a selection unit (28) that switches and selects a use heart sound waveform, which is a waveform used to obtain a heart beat interval, from the plurality of heart sound waveforms based on amplitude related information, which is information related to the magnitude of the amplitude of the heart sound waveform; an acquisition unit (29) that acquires the heartbeat interval calculated from the used heart sound waveform selected by the selection unit, The sensor unit is configured with a plurality of sensors that detect at least one of the first heart sound and the second heart sound, The sensor unit includes: a first bi-heart sound detection sensor (14) for detecting the first heart sound and the second heart sound; a second heart sound detection sensor (15) provided separately from the first heart sound detection sensor for detecting the first heart sound and the second heart sound, the amplitude fluctuation of which has an opposite characteristic to that of the heart sound detected by the first heart sound detection sensor; The cardiac waveform extraction unit includes: extracting a first heart sound waveform and a second heart sound waveform based on the heart sounds detected by the first and second heart sound detection sensors, and a first heart sound waveform and a second heart sound waveform based on the heart sounds detected by the second and second heart sound detection sensors; The selection unit selects, as the used heart sound waveform, selecting one of the first heart sound waveform and the second heart sound waveform based on the heart sounds detected by the first heart sound detection sensor, and one of the first heart sound waveform and the second heart sound waveform based on the heart sounds detected by the second heart sound detection sensor; Heart rate detection system.

6. A respiratory waveform extraction unit (23) that extracts a respiratory waveform from the biological vibration signal detected by the sensor unit, the amplitude-related information includes the respiratory waveform; The heart rate detection system according to any one of claims 1 to 5, wherein the selection unit selects the heart sound waveform to be used based on the respiratory waveform of the subject extracted by the respiratory waveform extraction unit.

7. A respiratory waveform extraction unit (23) that extracts a respiratory waveform from the biological vibration signal detected by the sensor unit; a ballistocardiogram waveform extraction unit (24) that extracts a ballistocardiogram waveform from the biological vibration signal detected by the sensor unit; A pulse waveform extraction unit (25) that extracts a pulse waveform from the biological vibration signal detected by the sensor unit; a learning processing unit (30) that performs a learning process to correct the heartbeat interval based on the heartbeat waveform so as to approach a true value by using relationships among a plurality of waveforms among the plurality of heartbeat waveforms extracted by the heartbeat waveform extraction unit, the respiratory waveform extracted by the respiratory waveform extraction unit, the ballistocardiographic waveform extracted by the ballistocardiographic waveform extraction unit, and the pulse waveform extracted by the pulse waveform extraction unit; Further equipped with 7. The heartbeat interval detection system according to claim 1, wherein the acquisition unit acquires the heartbeat interval corrected by the learning processing unit.

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