JP2023102612A - Heartbeat interval detection system - Google Patents

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

The present disclosure relates to heartbeat interval detection systems.

2. Description of the Related Art Conventionally, there has been known a device capable of detecting a person's health condition 24 hours a day by detecting vibrations caused by a person's respiratory activity or heartbeat with a vibration sensor. For example, Patent Literature 1 describes a biological vibration signal detection device that calculates a person's heartbeat rate or heartbeat interval from sound waves of heart sounds detected by a vibration sensor, or vibrations of ballistic or pulse waves. From the detected heartbeat interval information, it is possible to monitor fatigue, drowsiness, stress, wakefulness, and autonomic nervous state.

JP 2020-75136 A

However, in order to monitor a person's health condition with high accuracy as described above, a heartbeat interval accuracy of about 5 ms or less on average is required, but the above device has not achieved this. The present disclosure has been created in view of such points, and an object of the present disclosure is to provide a heartbeat interval detection system capable of calculating heartbeat intervals with high accuracy.

The present disclosure can be implemented as the following forms.

According to one aspect of the present disclosure, a heartbeat interval detection system is provided. A heartbeat interval detection system includes 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; heart sound waveform extraction units (21, 22) for extracting a plurality of heart sound waveforms based on the plurality of heart sounds detected by the sensor unit; A selection unit (28) for selection, and an acquisition unit (29) for acquiring the heartbeat interval calculated from the used heartbeat waveform selected by the selection unit.

According to this configuration, the selection unit switches and selects the heartbeat waveform to be used for acquiring the heartbeat interval based on the amplitude-related information, which is information about the magnitudes of the amplitudes of the plurality of heartbeat waveforms. Then, the heartbeat interval calculated from the used heartbeat waveform is obtained by the obtaining unit. Compared to the case where only one type of heart sound waveform is continuously used to obtain the heartbeat interval, according to this configuration, for example, as amplitude-related information, an appropriate heart sound waveform to be used can be appropriately selected from a plurality of heart sound waveforms according to conditions such as the magnitude of the amplitude value of the heart sound waveform and the respiratory state. Therefore, the heartbeat interval can be obtained with high accuracy.

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; FIG. It is a figure which shows an electrocardiogram waveform and a cardiac-sound waveform. 4 is a flowchart showing a heartbeat interval detection processing procedure executed by a heartbeat interval detection system; FIG. 10 is a graph showing deviation amounts from an electrocardiographic beat interval in the beat interval of the first heart sound and the beat interval of the second heart sound; FIG. 11 is a flowchart showing a heartbeat interval detection processing procedure executed by a heartbeat interval detection system according to the second embodiment of the present disclosure; FIG. FIG. 10 is a diagram showing a heart sound waveform after exhalation when a vibration sensor is placed on the subject's back; FIG. 10 is a diagram showing a heart sound waveform after inhalation when a vibration sensor is placed on the subject's back; It is a figure which shows an electrocardiographic waveform, an electrocardiographic waveform, a cardioballistic waveform, and a pulse waveform. It is a figure explaining the learning process by a learning process part. FIG. 11 is a schematic block diagram showing the functional configuration of a heartbeat interval detection system according to a third embodiment of the present disclosure; FIG. 11 is a flowchart showing a heartbeat interval detection processing procedure executed by a heartbeat interval detection system according to a third embodiment of the present disclosure; FIG. FIG. 12 is a diagram illustrating the usage and concept of the heartbeat interval detection system according to the fourth embodiment of the present disclosure; FIG.

A plurality of embodiments will be described below with reference to the drawings.
A. First embodiment:
A1. Configuration of heartbeat interval detection system 101:
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. FIG. The heartbeat interval detection system 101 of the first embodiment detects the heartbeat interval from the first heart sound and the second heart sound, which are a kind of biological vibration signals of the subject. In general, electrocardiography is considered to be the most reliable method for heart rate measurement, but electrocardiography requires electrodes to be attached directly to the body surface, and is constrained by cables during measurement. If the main purpose is to measure the state of heartbeat for medical purposes, etc., it is considered acceptable to give priority to reliability and be restricted. However, in the case of measuring emotions and stress conditions from heartbeat signals and expanding the application to a wider range of applications, for example, when the test subject is a driver who is driving a car, it is not preferable to be restrained by cables or the like.

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

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 a biological vibration signal, which is a signal indicating vibration generated from a living body, and heart sound, respiration, cardioballism, pulse, etc. that can be acquired based on the biological vibration signal. The vibration sensor 11 transmits the acquired signal to the signal processing unit 2 . The vibration sensor 11 preferably employs a highly sensitive sensor capable of detecting even very minute signals (for example, voltage of μV) in order to detect biological vibration signals.

The vibration sensor 11 detects heart sound information of the heart including mechanical or acoustic vibrations within the heart. Mechanical or acoustic vibrations in the heart are caused by the opening and closing of the valves of the heart, or by movement of blood in and out of the heart. The vibration sensor 11 is used by being attached to, for example, a region near the heart of the subject, and is capable of measuring vibration signals without restraining the subject. As for the appearance of the vibration sensor 11, it is preferable that it is in the form of a thin sheet or the like in terms of wearability. The vibration sensor 11 of the first embodiment corresponds to a "both heart sounds detection sensor" that detects the first heart sound and the second heart sound with one sensor.

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 cardioballistic 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 composed of a central processing unit (CPU), a microcomputer configured with a RAM and a ROM, etc. The central processing unit executes pre-installed programs to realize the functions of the above units. However, some or all of the functions of these units may be realized by hardware circuits.

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 that accompany the beating of the heart, and are elastic waves that propagate through media such as gases, liquids, and solids. Under normal conditions, heart sounds are periodic signals consisting of the first heart sound, which is generated due to the closing of the left and right atrioventricular valves at the beginning of ventricular systole, and the second heart sound, which is generated due to the closing of the aortic and pulmonary valves immediately after ventricular systole. In general, the first heart sound is low and long, and the second heart sound is high 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.

As shown as a heart sound waveform in FIG. 2, the period from the first heart sound to the next heart sound or the period from the second heart sound to the next second heart sound corresponds to the heartbeat interval HRI (Heart Rate Interval), and the number of first heart sounds or the number of second heart sounds in one minute corresponds to the heart rate. In the present embodiment, in order to distinguish heartbeat intervals based on each heart sound, the X-th heartbeat interval based on the first heart sound is defined as "first heartbeat interval HRIbx", and the X-th heartbeat interval based on the second heart sound is defined as "second heartbeat interval HRIcx". A heartbeat interval in which the first heart sound and the second heart sound are not distinguished is also simply referred to as "heartbeat interval HRI". Also, in FIG. 2, the X-th heartbeat interval in the electrocardiographic waveform is defined as an electrocardiographic heartbeat interval HRIax.

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 representing respiratory information from the biological vibration signal. The frequency of respiration is even lower than the frequency of the first heart sound. A cardioballistic waveform extracting unit 24 extracts a cardioballistic waveform from the biological vibration signal and also detects heartbeat timing.

A ballistic cardiogram is an oscillating waveform due to 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 heartbeat timing. A pulse waveform is a waveform resulting from changes in blood vessel volume due to pulsating blood flow. It is preferable that each of the extraction units 21, 22, 23, 24, and 25 appropriately performs processing for removing signals that become noise. For example, after appropriately enhancing the strength of the signal, it may be passed through a filter having a passband of a predetermined frequency range.

The first heart sound amplitude value acquisition unit 26 acquires the amplitude value of the first heart sound at the heartbeat timing of 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 of each beat from the second heart sound waveform. Hereinafter, the amplitude value of the X-th first heart sound among the extracted waveforms will be referred to as "first heart sound amplitude value Abx", and the amplitude value of the X-th second heart sound will be referred to as "second heart sound amplitude value Acx".

The heart sound waveform selection unit 28 switches and selects a heart sound waveform to be used, which is a waveform used for acquiring heartbeat intervals, from among a plurality of heart sound waveforms, based on amplitude-related information, which is information relating to the magnitude of the amplitude of the heart sound waveform. In this embodiment, the use heart sound waveform selection unit 28 selects either the first heart sound waveform or the second heart sound waveform as the use heart sound waveform. The first heart sound amplitude value Abx corresponds to "amplitude related information". A processing procedure for selecting the heartbeat waveform to be used will be described later.

The heartbeat interval obtaining unit 29 obtains 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 used heartbeat waveform selected by the use heartbeat waveform selection unit 28 . Note that the heartbeat interval may be calculated before selecting the heartbeat waveform to be used. 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. Further, the output unit 3 may 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. Since heart sounds, respiration, cardioballism, and pulses have different frequency bands, all information can be obtained with a single vibration sensor 11 .

The learning processing unit 30 performs a learning process of correcting the heartbeat interval based on the heartbeat waveform so as to approach the true value, using the relationships among the plurality of heartbeat waveforms, respiratory waveforms, cardioballistic waveforms, and pulse waveforms. Details of the learning process will be described later.

A2. Heartbeat interval detection processing by the heartbeat interval detection system 101:
Next, a heartbeat interval detection processing procedure executed by the heartbeat interval detection system 101 described above will be described. The processing shown in FIG. 3 is repeatedly executed at predetermined time intervals or according to the processing in the heartbeat interval detection system 101 as appropriate. As shown in FIG. 3 , in step 10 (hereinafter step is abbreviated as “S”), the vibration signal measured by the vibration sensor 11 is received by the signal processing section 2 . Next, at 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 a first heart sound waveform, and the second heart sound waveform extraction unit 22 extracts a second heart sound waveform.

Then, in S30, the heartbeat timings of the first heartbeat waveform and the second heartbeat waveform 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.

Next, at S40, the amplitude values of the first heart sound and the second heart sound are obtained. Specifically, the first heart sound amplitude value acquisition unit 26 acquires the first heart sound amplitude value Abx, and the second heart sound amplitude value acquisition unit 27 acquires the second heart sound amplitude value Acx. Then, in S50, the used heart sound waveform selector 28 determines whether or not the first heart sound amplitude value Abx is equal to or greater than the threshold value. This determination is made for each beat.

The threshold may be, for example, a value determined in advance by experiments or the like as the lower limit of the standard first heart sound amplitude value of the subject. Alternatively, the threshold may be set to a constant percentage value (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, which together constitutes one beat.

If the first heart sound amplitude value Abx is greater than or equal to the threshold value (S50: YES), the process proceeds to S60, where the heartbeat interval obtaining unit 29 calculates the first heart sound heartbeat 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 obtaining unit 29 calculates the second heart sound heartbeat interval HRIcx. After S60 and S70, the calculated heartbeat intervals HRIbx and HRIcx are output to the output unit 3 in S80. After the processing of S80, this processing routine ends.

The judgment processing in S50 will be described in detail using an example. As described above, the first heart sound and the second heart sound form one beat. Hereinafter, these beats are referred to as the first beat, the second beat, the third beat, . . . in order from the left in FIG. 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, and the other first heart sound amplitude values Abx are above the threshold.

In this case, the heartbeat waveform selection unit 28 selects the first heartbeat waveform as the heartbeat waveform to be used for detecting the first heartbeat interval corresponding to the first and second heartbeats, and selects the second heartbeat waveform for detecting the second and third heartbeat intervals corresponding to the second and third heartbeats and the third and fourth heartbeats, respectively. Therefore, the heartbeat intervals eventually adopted are, in chronological order, the first heart sound interval HRIb1, the second heart sound interval HRIc2, the second heart sound interval HRIc3, the first heart sound interval HRIb4, and so on.

As described above, compared to the second heart sound, the first heart sound basically has a lower frequency intensity and a larger amplitude value. Therefore, it is preferable to use the first heart sound waveform as the base of the heart sound waveform to be used. This is because the larger the amplitude value, the smaller the possibility of erroneous detection of a large waveform caused by the influence of electronic noise or other disturbances, as compared to the case where the amplitude value is small. However, if the first heart sound can be detected temporarily, but the detection accuracy of the first heart sound is temporarily lowered due to respiratory conditions or other unexpected disturbances, the accuracy can be further improved by using the second heart sound waveform as the heart sound waveform to be used. 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 according to the determination result as to whether the first heart sound amplitude value Abx is equal to or greater than the threshold value.

A3. Correction processing of second heart sound beat interval HRIcx:
Next, correction processing of the second heart sound heartbeat interval HRIcx by the learning processing unit 30 will be described. In FIG. 4, the horizontal axis represents time, and the vertical axis represents the amount of deviation ΔHRI from the electrocardiographic heartbeat interval HRIax. In FIG. 4, the amount of deviation ΔHRI in the first heart sound interval HRIbx is indicated by black circles, and the amount of deviation ΔHRI in the second heart sound interval HRIcx is indicated by white circles. Further, the amount of deviation ΔHRI for the heartbeat intervals HRIbx and HRIcx acquired by the heartbeat interval acquiring unit 29 is connected by a solid line in the time lapse direction.

As shown in FIG. 4, the first heart sound waveform is selected as the use heart sound waveform from time T0 to T1 and time T2 onwards, and the second heart sound waveform is selected as the use heart sound waveform from time T1 to T2. Time T1 to T2 is a region where the first heart sound amplitude value Abx is smaller than the threshold. From time T0 to T1 and after time T2, the first heart sound amplitude value Abx is a sufficiently large region that is equal to or greater than the threshold. The learning processing unit 30 uses, for example, a well-known machine learning model to perform learning so that the first heart sound heartbeat interval HRIbx in the region where the first heart sound amplitude value Abx is sufficiently large is the true value, and the second heart sound heartbeat interval HRIcx is brought closer to the true value. As time elapses, the accuracy of the second heart sound interval HRIcx approaches the accuracy of the first heart sound interval HRIbx.

The data corrected by learning by the learning processing unit 30 is transmitted to the heartbeat interval acquisition unit 29 . The heartbeat interval acquiring unit 29 acquires the corrected second heartbeat interval HRIcx when the second heartbeat waveform is selected as the heartbeat waveform to be used. As a result, it is possible to improve the accuracy in the interval in which the second heart sound heart beat interval HRIcx is selected.

[effect]
(1) In the heartbeat interval detection system 101 of the first embodiment, the heart sound waveform to be used is appropriately switched between the first heart sound and the second heart sound according to the determination result as to whether the first heart sound amplitude value Abx is equal to or greater than the threshold value. Therefore, when the first heart sound can be detected, but the detection accuracy of the first heart sound is temporarily lowered, the heartbeat interval can be calculated with high accuracy by using the second heart sound waveform as the used heart sound waveform.

(2) Furthermore, in the heartbeat interval detection system 101 of the first embodiment, the learning processing unit 30 can correct the second heart sound heartbeat interval HRIcx so as to be closer to the true value. Therefore, it is possible to improve the detection accuracy of the heartbeat interval HRIcx of the second heart sound in the section in which the second heart sound is selected as the heartbeat waveform to be used.

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. 5-9. In addition, in several embodiments described below, the same code|symbol is attached|subjected about the structure similar to 1st Embodiment, and description is abbreviate|omitted. The second embodiment is similar to the first embodiment in the overall configuration of the heartbeat interval detection system 101 shown in FIG. Specific description will be given below in order.

B1. Heartbeat interval detection processing by the heartbeat interval detection system:
In the second embodiment, the respiratory waveform is used instead of the amplitude value as the amplitude-related information when selecting the heartbeat waveform to be used. The processes (S10, S20, S30) up to the detection of the heartbeat timings in the first and second heartbeat waveforms are the same as those in the first embodiment. Instead of acquiring the amplitude values of the first and second heart sounds (S40) and determining the threshold value (S50) in the first embodiment, in the second embodiment, in S51 shown in FIG. This determination is made for each beat. In this embodiment, it is assumed that the vibration sensor 11 is arranged on the subject's back.

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

According to experiments conducted by the present inventor, when the vibration sensor 11 is placed on the back of the subject, the first heart sound amplitude value Abx is larger than the second heart sound amplitude value Acx after exhalation as shown in FIG. 6, and the first heart sound amplitude value Abx is smaller than the second heart sound amplitude Acx after inhalation as shown in FIG. Therefore, the first heart sound amplitude value Abx, which provides a larger amplitude value, is adopted from the latter half to the first half of inspiration, which is close to the state after exhalation, and the second heart sound amplitude value Acx, which provides a larger amplitude value, is adopted from the latter half to the first half of expiration, which is close to the state after inhalation.

That is, in the second embodiment, based on the respiratory information obtained from the respiratory waveform, the cardiac waveform having a larger amplitude value can be switched and selected from the first cardiac waveform and the second cardiac waveform as the used cardiac waveform. The processes of S60, S70, and S80 are the same as those of the first embodiment.

B2. Learning processing for improving the accuracy of the first and second heartbeats:
Next, learning processing for improving the accuracy of the first heart sound waveform and the second heart sound waveform by the learning processing unit 30 will be described. As shown in FIG. 8, the times at which peaks appear in the heart sound, cardiotrajectory, and pulse with respect to the electrocardiogram are generally determined. Note that the position of this peak varies depending on the position where the vibration sensor 11 is arranged. Based on the relationship between these waveforms, the heartbeat point of the heart sound is corrected to be closer to the true value. In this system, since no electrocardiographic waveform is obtained, specifically, the true value is obtained from each of the five extracted waveforms (first heart sound waveform, second heart sound waveform, cardioballistic waveform, pulse waveform, respiratory waveform), for example, by means of an average value, etc., and the peak positions of the first heart sound and the second heart sound are corrected for the obtained true value.

In FIG. 9, the horizontal axis represents time, and the vertical axis represents the amount of deviation ΔHRI from the electrocardiographic heartbeat interval HRIax. As shown in FIG. 9, the deviation amount ΔHRI of the heartbeat interval calculated based on each heartbeat waveform whose peak position is corrected becomes smaller after the elapse of time after learning and correction, and the accuracy of heartbeat interval acquisition can be improved.

C. Third embodiment:
Next, the heartbeat interval detection system 103 of the third embodiment of the present disclosure will be described with reference to FIGS. 10 and 11. FIG. As shown in FIG. 10, the sensor unit 1 included in the heartbeat interval detection system 103 of the third embodiment has a plurality of (two in this embodiment) sensors. The sensor unit 1 has a first heart sound detection sensor 12 exclusively for detecting the first heart sound and a second heart sound detection sensor 13 for exclusively 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.

The first heart sound detection sensor 12 can be placed at a site where the first heart sound is likely to be received relatively strongly, for example, the lower part of the ventral chest area of the subject, based on the principle of generation of the first heart sound. Similarly, the second heart sound detection sensor 13 can be placed in a region where the second heart sound is likely to be received relatively strongly, for example, in the upper chest area on the back side of the subject, based on the principle of generating the second heart sound. It should be noted that this arrangement of the sensors is just an example, and can be changed as appropriate since the positions at which strong heart sounds can be picked up differ depending on the subject.

As shown in FIG. 11, in the third embodiment, each heart sound is received by sensors 12 and 13 dedicated to detecting each heart sound. At S<b>11 , the vibration signal measured by the first heart sound detection sensor 12 is received by the signal processor 2 . Next, in S21, a first heart sound waveform is extracted by the first heart sound waveform extraction unit 21 based on the received vibration signal. Then, in S31, the heartbeat timing in the first heartbeat waveform is detected. Next, in S41, the first heart sound amplitude value acquisition unit 26 acquires the first heart sound amplitude value Abx.

For the second heart sound, the second heart sound amplitude value Acx is obtained by the second heart sound detection sensor 13 through the same processing (S12, S22, S32, S42) as 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 processes 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 processes 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 processes may be executed simultaneously or sequentially. Good. The processes of S50, S60, S70, and S80 are the same as those of the first embodiment.

According to the heartbeat interval detection system 103 of the third embodiment, the first heart sound detection sensor 12 detects the first heart sound, and the second heart sound detection sensor 13 detects the second heart sound. Therefore, depending on the arrangement of the sensors 12 and 13, both heart sounds can be detected as strong signals with large waveforms, so that the amplitude value can be increased. Therefore, the detection accuracy of each heart sound can be improved. Also, along with this, it may be possible to continue to use the first heart sound waveform as the working heart sound waveform even if the amplitude value is temporarily reduced. Furthermore, even when the second heart sound waveform is used as the heart sound waveform to be used, the detection accuracy can be improved because the amplitude value is large. As a result, the heartbeat interval acquisition accuracy of the heartbeat interval acquiring unit 29 can be improved.

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. The sensor unit 1 included in the heartbeat interval detection system of the fourth embodiment has a plurality of sensors as in the third embodiment. Although the system configuration diagram is omitted, a first bilateral heart sound detection sensor 14 is provided in place of the first heart sound detection sensor 12 in the third embodiment, and a second bilateral heart sound detection sensor 15 is provided in place of the second heart sound detection sensor 13 in the third embodiment.

The first and second heart sounds detecting sensors 14 and 15 in the fourth embodiment differ from the third embodiment in that they detect both the first heart sound and the second heart sound, respectively. The first bilateral heart sound detection sensor 14 and the second bilateral heart sound detection sensor 15 detect heart sound waveforms whose amplitude variations are opposite to each other. To detect the opposite characteristics, for example, the first bilateral heart sound detection sensor 14 is placed on the ventral side of the subject 100, and the second bilateral heart sound detection sensor 15 is placed on the dorsal side of the subject 100, as shown in FIG.

Here, the amplitude fluctuation means the temporal periodic fluctuation of the amplitude intensity of the heart sound, and as shown on the right side of FIG. In addition, the reverse characteristic means a characteristic in which peaks and troughs of the waveform of the amplitude fluctuation are reversed due to a shift in the time at which the peak appears in the amplitude fluctuation.

Also in the fourth embodiment, in substantially the same manner as in each of the above-described embodiments, an optimum waveform is appropriately selected as the heartbeat waveform to be used from among a plurality of heartbeat waveforms. In this embodiment, a total of four waveforms, the first and second heart sound waveforms detected by the first bilateral heart sound detection sensor 14 and the first and second heart sound waveforms detected by the second bilateral heart sound detection sensor 15, are obtained. Among these waveforms, the waveform having the largest amplitude value in the time series can be preferentially selected as the heartbeat waveform to be used to calculate the heartbeat interval.

In addition, for example, as a base, the first heart sound waveform detected by the first heart sound detection sensor 14 may be used as the heart sound waveform to be used, and if the amplitude value of the first heart sound waveform detected by the first heart sound detection sensor 14 is smaller than the threshold as in the first embodiment, 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.

Furthermore, in combination with respiration information, a heart sound waveform that can take a larger amplitude value may be switched and selected as the heart sound waveform to be used. For example, the respiratory state may be determined, and if the period is from the latter half of inspiration to the first half of expiration, the second heart sound waveform detected by the second bilateral heart sound detection sensor 15 on the back side may be selected as the heart sound waveform to be used.

As described above, according to the heartbeat interval calculation system of the fourth embodiment, a plurality of heart sound waveforms having opposite characteristics can be obtained with respect to the first heart sound and the second heart sound. Therefore, the number of combinations of waveforms that can be selected as heart sound waveforms to be used increases, and the optimal heart sound waveform can be appropriately selected according to the situation.

E. Other embodiments:
(E1) In the first embodiment, the amplitude threshold value may be changed as appropriate when data is accumulated over time. For example, it can be changed as appropriate, such as by setting it to an arbitrary constant value at the beginning of the measurement, and then changing it to a value that is 80% of the maximum amplitude value so far when the data are accumulated.

(E2) In the third and fourth embodiments, the sensor section 1 may be configured to have three or more sensors.

(E3) In the above-described third embodiment, the heartbeat waveform to be used may be selected by determining the respiratory state. In that case, in the flowchart shown in FIG. 11, the process of S51 in the flowchart shown in FIG. 5 may be performed instead of the processes of S41, S42, and S50.

(E4) By combining the first embodiment and the second embodiment, the determination based on the threshold value of the amplitude value and the determination based on the respiration information may be combined. For example, after the threshold determination, the respiration information may be taken into account to finally determine the heartbeat waveform to be used.

The present disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from the scope of the present disclosure. For example, the technical features in each embodiment corresponding to the technical features in the form described in the outline of the invention can be appropriately replaced or combined in order to solve some or all of the above-described problems or achieve some or all of the above-described effects. Also, if the technical features are not described as essential in this specification, they can be deleted as appropriate.

Reference Signs List 1 sensor unit 2 signal processing unit 3 output unit 11 biological vibration signal detection sensor (biheart sound detection sensor) 12 first heart sound detection sensor 13 second heart sound detection sensor 14 first bi-heart sound detection sensor 15 second bi-heart sound detection sensor 21 first heart sound waveform extraction unit 22 second heart sound waveform extraction unit 23 respiratory waveform extraction unit 24 cardioballistic 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 Heartbeat interval acquisition unit 30 Learning processing unit 100 Examinee 101, 103 Heartbeat interval detection system

Claims (8)

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);
heart sound waveform extraction units (21, 22) for extracting a plurality of heart sound waveforms based on the plurality of heart sounds detected by the sensor unit;
a selection unit (28) for switching and selecting, from among the plurality of heart sound waveforms, a heart sound waveform to be used, which is a waveform used to obtain a heartbeat interval, based on amplitude-related information, which is information relating to the magnitude of the amplitude of the heart sound waveform;
an acquisition unit (29) for acquiring the heartbeat interval calculated from the used heartbeat waveform selected by the selection unit;
heartbeat interval detection system. The sensor unit has a bi-heart sound detection sensor (11) for detecting the first heart sound and the second heart sound,
The heart sound waveform extraction unit extracts a first heart sound waveform based on the first heart sound and a second heart sound waveform based on the second heart sound,
The amplitude-related information includes an amplitude value of the first heart sound waveform;
The selection unit uses, as the heartbeat waveform to be used,
2. The heartbeat interval detection system of claim 1, wherein the first heart sound waveform is selected when the amplitude value of the first heart sound is greater than or equal to a threshold value, and the second heart sound waveform is selected when the amplitude value of the first heart sound is less than the threshold value. 3. The heartbeat interval detection system according to claim 2, wherein said threshold is set to the same value as the amplitude value of said second heart sound forming the same beat as said first heart sound. 2. The heartbeat interval detection system according to claim 1, wherein said sensor unit is composed of a plurality of sensors for detecting at least one of said first heart sound and said second heart sound. 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,
5. The heartbeat interval detection system according to claim 4, wherein the heart sound waveform extraction unit extracts a first heart sound waveform based on the first heart sound detected by the first heart sound detection sensor and a second heart sound waveform based on the second heart sound detected by the second heart sound detection sensor. The sensor unit is
a first bi-heart sound detection sensor (14) for detecting said first heart sound and said 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 having amplitude fluctuation characteristics opposite to those of the heart sounds detected by the first heart sound detection sensor;
The cardiac waveform extraction unit
Extracting a first heart sound waveform and a second heart sound waveform based on the heart sounds detected by the first double heart sound detection sensor and a first heart sound waveform and a second heart sound waveform based on the heart sounds detected by the second heart sound detection sensor;
The selection unit uses, as the heartbeat waveform to be used,
5. The heartbeat interval detection system of claim 4, wherein one of a first heart sound waveform and a second heart sound waveform based on the heart sounds detected by the first double heart sound detection sensor and one of the first heart sound waveform and a second heart sound waveform based on the heart sounds detected by the second double heart sound detection sensor are selected. further comprising a respiratory waveform extraction unit (23) for extracting a respiratory waveform from the biological vibration signal detected by the sensor unit;
The amplitude-related information includes the respiratory waveform,
The heartbeat interval detection system according to any one of claims 1 to 6, wherein the selection unit selects the use heartbeat waveform based on the respiratory waveform of the subject extracted by the respiratory waveform extraction unit. a respiratory waveform extraction unit (23) for extracting a respiratory waveform from the biological vibration signal detected by the sensor unit;
a cardioballistic waveform extraction unit (24) for extracting a cardioballistic waveform from the biological vibration signal detected by the sensor unit;
a pulse waveform extraction unit (25) for extracting a pulse waveform from the biological vibration signal detected by the sensor unit;
a learning processing unit (30) that performs a learning process of correcting the heartbeat interval based on the cardiac waveform so as to approach a true value, using relationships among a plurality of waveforms among the plurality of cardiac waveforms extracted by the cardiac waveform extracting unit, the respiratory waveform extracted by the respiratory waveform extracting unit, the cardiac ballistic waveform extracted by the cardiac ballistic waveform extracting unit, and the pulse waveform extracted by the pulse waveform extracting unit;
further comprising
The heartbeat interval detection system according to any one of claims 1 to 7, wherein the acquisition unit acquires the heartbeat interval corrected by the learning processing unit.

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