WO2022215191A1

WO2022215191A1 - Heartbeat detection method and heartbeat detection device

Info

Publication number: WO2022215191A1
Application number: PCT/JP2021/014756
Authority: WO
Inventors: 伸昭松浦; 啓桑原; 利彦近藤
Original assignee: 日本電信電話株式会社
Priority date: 2021-04-07
Filing date: 2021-04-07
Publication date: 2022-10-13
Also published as: JPWO2022215191A1; JP7491466B2

Abstract

This heartbeat detection device includes: an index value calculating unit (5) that calculates, for each sampling time, index values from a sampling data string of an ECG waveform of a living body; a threshold value determining unit (6) that compares a threshold value for heartbeat detection with the lower limit of the range being likely as a threshold value derived from the ECG waveform of the living body; a heartbeat time determining unit (7) that determines the sampling time of the peak as a heartbeat time when the threshold value determining unit (6) determines that the threshold value is not less than the lower limit, and detects an index value peak exceeding the threshold value; and a threshold value setting unit (8) that renews the threshold value on the basis of the index value peak exceeding the current threshold value.

Description

Heartbeat detection method and heartbeat detection device

The present invention relates to a heartbeat detection method and a heartbeat detection device for detecting heartbeats (R waves) from an electrocardiogram waveform.

The ECG (Electrocardiogram) waveform is an observation of the electrical activity of the heart and consists of a continuous heartbeat waveform. One heartbeat waveform consists of components such as P wave, Q wave, R wave, S wave, T wave, etc., which reflect the activity of the atria and ventricles. Of these waves, the R wave accompanies the contraction of the ventricle, and since it has a large amplitude, the heartbeat is often detected based on the R wave.

A simple method for detecting heartbeats (R waves) from ECG waveforms is to detect peaks in a time series. That is, a certain threshold is set for the data time series, and when the ECG waveform exceeds the threshold, it is determined as an R wave.

FIG. 5 is a flow chart explaining a conventional heartbeat detection method. When an ECG waveform value is input (step S100 in FIG. 5), the heartbeat detection device calculates an index value based on the ECG waveform value and the previous ECG waveform value (step S101 in FIG. 5). Next, the heartbeat detection device compares the index value and the threshold value (step S102 in FIG. 5), determines a heartbeat when the index value exceeds the threshold value (step S103 in FIG. 5), and determines that the index value is equal to or less than the threshold value. Occasionally, it is not determined as a heartbeat. Then, the heartbeat detection device updates the threshold using the index value and the previous index value (step S104 in FIG. 5). By adaptively updating the threshold value, it is possible to perform heartbeat detection that reflects changes in the signal level due to, for example, the wearing state of electrodes on the subject.

As such a conventional heartbeat detection method, there is a method disclosed in Patent Document 1. In the method disclosed in Patent Literature 1, the index value is not reflected in the threshold when it is unlikely that the index value is derived from the ECG waveform. As a result, it is possible to prevent the threshold value from jumping due to large noise mixed in the ECG waveform, and there is an advantage that the heart rate can be detected accurately.

However, with the method disclosed in Patent Document 1, there is a possibility that a waveform with a small amplitude that is considered inappropriate as an R wave may be mistakenly recognized as an R wave.

Japanese Patent No. 6652655

The present invention has been made to solve the above problems, and an object of the present invention is to provide a heartbeat detection method and a heartbeat detection device that do not erroneously recognize peaks with too small amplitudes as heartbeats.

A heartbeat detection method of the present invention includes a first step of calculating an index value from a sampled data string of an electrocardiogram waveform of a living body at each sampling time, and a threshold value for heartbeat detection and a threshold derived from the electrocardiogram waveform of a living body. a second step of comparing with the lower limit of the likely range; and determining in the second step that the threshold is equal to or greater than the lower limit, and when a peak of the index value exceeding the threshold is detected, the peak and a third step of setting the sampling time to the heartbeat time, and not performing heartbeat detection by comparing the threshold and the index value when the threshold is determined to be less than the lower limit in the second step. It is characterized.

Further, the heartbeat detection apparatus of the present invention includes: an index value calculation unit configured to calculate an index value from a sampled data string of an electrocardiogram waveform of a living body at each sampling time; a threshold determination unit configured to compare the lower limit of a plausible range as the threshold derived from the threshold determination unit determines that the threshold is equal to or greater than the lower limit, and the index value exceeding the threshold a heartbeat time determination unit configured to set the sampling time of the peak as the heartbeat time when a peak is detected, wherein the heartbeat time determination unit determines that the threshold value is less than the lower limit value. , heartbeat detection by comparison between the threshold value and the index value is not performed.

According to the present invention, if the threshold value is less than the lower limit value, heartbeats are not detected even if the index value exceeds the threshold value. Heart rate detection can be performed on

FIG. 1 is a block diagram showing the configuration of a heartbeat detection device according to an embodiment of the present invention. FIG. 2 is a flowchart illustrating a heart rate detection method according to an embodiment of the invention. FIG. 3 is a flow chart for explaining the operation of the threshold value setting section of the heartbeat detection device according to the embodiment of the present invention. FIG. 4 is a block diagram showing a configuration example of a computer that implements the heartbeat detection device according to the embodiment of the present invention. FIG. 5 is a flowchart illustrating a conventional heartbeat detection method.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a heartbeat detection device according to an embodiment of the invention, and FIG. 2 is a flow chart for explaining a heartbeat detection method according to an embodiment of the invention. The heartbeat detection apparatus includes an electrocardiograph 1 for outputting an ECG waveform sampling data string, a storage unit 2 for storing an ECG waveform sampling data string and sampling time information, and sampling data from the ECG waveform sampling data string. A positive/negative inversion value calculation unit 3 that calculates the positive/negative inversion value of the time difference for each sampling time, and a positive/negative inversion value in a certain time range before the sampling time to be processed and a certain value after the sampling time to be processed. A maximum value detection unit 4 that detects the maximum value of the positive/negative reversed values in the time range at each sampling time, and an index that calculates an index value obtained by subtracting the maximum value from the positive/negative reversed value at the sampling time to be processed at each sampling time. A value calculation unit 5, a threshold determination unit 6 that compares the threshold value for heartbeat detection with the lower limit value of a range that is likely to be a threshold value derived from the ECG waveform of the living body, and a threshold value that is determined to be equal to or higher than the lower limit value, and exceeds the threshold value. A heartbeat time determining unit 7 for setting the sampling time of the peak when the peak of the index value is detected to be the heartbeat time, and a threshold setting unit 8 for updating the threshold based on the peak of the index value exceeding the current threshold. .

The maximum value detection unit 4 includes a FIFO buffer (First In, First Out) 40 to which the time difference positive/negative inversion value calculated by the positive/negative inversion value calculation unit 3 is input, and a FIFO buffer to which the output value of the FIFO buffer 40 is input. 41, a FIFO buffer 42 to which the output value of the FIFO buffer 41 is input, and sampling the maximum value of the positive/negative inverted value of the time difference stored in the FIFO buffer 40 and the inverted positive/negative value of the time difference stored in the FIFO buffer 42. It is composed of a detection processing unit 43 that detects each time.

The index value calculation unit 5 detects the maximum value detected by the maximum value detection unit 4 from the FIFO buffer 50 to which the time difference positive/negative inversion value calculated by the positive/negative value calculation unit 3 is input, and the output value of the FIFO buffer 50. and a subtraction processing unit 51 that calculates an index value obtained by subtracting , at each sampling time.

The heartbeat detection method of this embodiment will be described below. Here, the procedure from detecting one heartbeat to obtaining the heartbeat time will be described. Time-series data of heartbeat times is obtained by repeating such calculation of heartbeat times over the period of the ECG waveform data.

In this embodiment, D(i) is the data string obtained by sampling the ECG waveform. i (i=1, 2, . . . ) is a number given to data of one sampling. Needless to say, the larger the number i, the later the sampling time.

The electrocardiograph 1 measures an ECG waveform of a living body (human body) (not shown) and outputs a sampling data string D(i) of the ECG waveform. At this time, the electrocardiograph 1 adds sampling time information to each sampling data and outputs the data. Since the specific method of measuring the ECG waveform is a well-known technique, detailed description thereof will be omitted.
The storage unit 2 stores the sampling data sequence D(i) of the ECG waveform output from the electrocardiograph 1 and the information on the sampling time.

In order to calculate the time difference positive/negative inversion value Y(i) of the sampling data D(i), the positive/negative inversion value calculation unit 3 calculates the data D(i+1) after one sampling of the sampling data D(i) and the data D(i+1) one sampling before. Data D(i-1) are obtained from the storage unit 2 (step S1 in FIG. 2). Then, the positive/negative inversion value calculator 3 calculates the time difference positive/negative inversion value Y(i) of the sampling data D(i) for each sampling time as shown in the following equation (step S2 in FIG. 2).
Y(i)=-{D(i+1)-D(i-1)} (1)

The positive/negative inversion value calculation unit 3 inputs the calculated time difference positive/negative inversion value Y(i) to the FIFO buffer 50 at each sampling time (step S3 in FIG. 2). The input value is held in the FIFO buffer 50, and after a time corresponding to the size of the FIFO buffer 50 (the delay time from when the positive/negative time difference value is input to the FIFO buffer 50 until it is output), It will be used for subtraction processing.

In addition, the positive/negative inversion value calculation unit 3 inputs the calculated time difference positive/negative inversion value Y(i) to the FIFO buffer 40 at each sampling time (step S4 in FIG. 2). The output of FIFO buffer 40 is input to FIFO buffer 41 (step S5 in FIG. 2), and the output of FIFO buffer 41 is input to FIFO buffer 42 (step S6 in FIG. 2). The FIFO buffers 40 to 42 are for obtaining the maximum value of the time difference positive/negative inversion value within a certain time range.

The time interval L3 corresponding to the length of the FIFO buffer 41 (the delay time from when the time difference positive/negative inversion value is input to the FIFO buffer 41 until it is output) is the width of the peak derived from the R wave (approximately 10 ms). ), preferably about 50 ms. Also, a time interval L2 corresponding to the length of the FIFO buffer 40 (a delay time from when the time difference positive/negative inversion value is input to the FIFO buffer 40 until it is output), and a time interval corresponding to the length of the FIFO buffer 42 L4 (the delay time from when the time difference positive/negative inversion value is input to the FIFO buffer 42 until it is output, L2=L4) is appropriately about 100 ms. Also, the time interval L1 corresponding to the length of the FIFO buffer 50 may be L1=L2+L3/2. Therefore, in the above numerical example, L1 is 125 ms. By setting L1=L2+L3/2 and L2=L4, the range of -(L2+L3/2) to -(L3/2) is obtained for the time (sampling time to be processed) of the output value a of the FIFO buffer 50. The maximum value M can be obtained for the range from (L3/2) to (L2+L3/2), and the maximum value M can be subtracted from the output value a.

The detection processing unit 43 detects the maximum value M of the time difference positive/negative inversion value stored in the FIFO buffer 40 and the time difference positive/negative inversion value stored in the FIFO buffer 42 at each sampling time (step S7 in FIG. 2). .
The subtraction processing unit 51 calculates an index value b=a−M by subtracting the maximum value M from the output value a of the FIFO buffer 50 at each sampling time (step S8 in FIG. 2).

Next, the threshold determination unit 6 compares the current threshold Th for heartbeat detection with the lower limit value Thmin of the plausible range as the threshold Th derived from the ECG waveform of the living body (step S9 in FIG. 2). A likely range for the threshold Th derived from the ECG waveform of the living body can be determined based on past measurement results. The initial value of the threshold Th may be set in advance to an arbitrary value within a plausible range as the threshold Th.

When the threshold determination unit 6 determines that the current threshold value Th is equal to or greater than the lower limit value Thmin (YES in step S9), the heartbeat time determination unit 7 detects a peak of the index value b(i) exceeding the threshold value Th (Fig. 2: YES at step S10), the sampling time of this peak is set as the heartbeat time (step S11 in FIG. 2).

The sampling time of the index value b(i) refers to the sampling time of the time difference positive/negative inversion value Y(i) on which the index value b(i) is based (the sampling time of the data D(i)). The sampling time of the index value b(i) can be acquired from the storage unit 2 .

Further, the heartbeat time determining unit 7 detects a peak of the index value b(i) exceeding the threshold Th when the threshold determining unit 6 determines that the current threshold Th is less than the lower limit Thmin (NO in step S9). If not (NO in step S10), the heartbeat (R wave) is not determined and the heartbeat time is not determined.

Next, the threshold setting unit 8 updates the threshold Th based on the peak of the index value b(i) exceeding the current threshold Th (step S12 in FIG. 2). FIG. 3 is a flow chart for explaining the operation of the threshold setting unit 8 (step S12).

First, the threshold setting unit 8 determines whether or not a peak of the index value b(i) exceeding the current threshold Th has been detected (step S20 in FIG. 3). If the above peaks can be continuously detected (YES in step S21 in FIG. 3), the average value bave of the newest predetermined number V of these peaks is obtained, and this average value bave is given a predetermined coefficient α (For example, α=0.4) is multiplied to obtain a threshold candidate Thc (step S22 in FIG. 3).
Thc=α×bave (2)

The threshold setting unit 8 compares the calculated threshold candidate Thc with a threshold limit value L based on the current threshold Th and the difference limit value that can be said to be plausible as the time difference positive/negative inversion value of the ECG waveform of the living body. When the candidate Thc exceeds the threshold limit value L, the threshold Th is not updated (YES in step S23 of FIG. 3). threshold value Th (step S24 in FIG. 3). The threshold limit value L will be described later.

The threshold setting unit 8 performs the above processing at each sampling time. When the peak of the index value b(i) exceeding the threshold value Th is continuously detected, the process of step S22 is repeatedly executed to sequentially calculate the threshold candidate Thc, and the threshold candidate Thc becomes the threshold value. If it is equal to or less than the limit value L, the threshold Th is updated.

Here, when the peak of the index value b(i) exceeding the threshold Th is not detected for 3 seconds (YES in step S25 in FIG. 3), the threshold setting unit 8 resets the peak search operation and sets the threshold Th. is redone (step S26 in FIG. 3). Specifically, the threshold setting unit 8 obtains the maximum value bmax using the data of the index value b(i) in a period of 2 seconds after resetting the peak search operation, and sets the maximum value bmax to a predetermined value. A value multiplied by a coefficient β (eg, β=0.4) is set as a new threshold value Th.
Th=β×bmax (3)

Thus, in this embodiment, by repeating the processing of steps S1 to S12 in FIG. 2 at each sampling time, time-series data of heartbeat times can be obtained.

Here, what is the maximum value of the time difference positive/negative inversion value of the ECG waveform of the living body (human body)? think about. The QRS interval (from the beginning of the Q wave to the end of the S wave) is 0.06-0.1 s.

The time from the maximum value of the R wave to the minimum value of the S wave can be considered to be about 15 to 25 ms as 1/4 of the QRS interval. Furthermore, the sharpest change occurs near the center of the range from the highest value of the R wave to the lowest value of the S wave. Assuming that the time range is about half from the maximum value of the R wave to the minimum value of the S wave, it is estimated to be about 7.5 to 12.5 ms. If there is a change in the electrocardiographic potential corresponding to the QRS amplitude during this time, the rate of change in the electrocardiographic potential is considered to be about 350 μV/ms at maximum. If the change rate of the electrocardiographic potential is converted into the positive/negative inversion value of the time difference obtained by the equation (1), it becomes 700 μV when the sampling interval is 1 ms, and is further rounded to 1000 μV with a margin.

From the above, it can be said that when the sampling interval is 1 ms, the time difference positive/negative inversion value exceeding 1000 μV is not likely to be the time difference positive/negative inversion value of the human ECG waveform. This standard is 5000 μV when the sampling interval is 5 ms. That is, if the sampling interval is dT, the difference limit value X, which can be said to be plausible as the time difference positive/negative inversion value of the human ECG waveform, can be expressed as follows.
X=dT[ms]×1000[μV] (4)

The index value b represents the height of the clearance of the time difference value in the surrounding time domain with respect to the peak derived from the R wave. When the noise presents a sharp unimodal peak, in the worst case the value is reflected in the index value b as it is.

If the value obtained by multiplying the average value bave of the peaks of a predetermined number V (in this embodiment, V=5) exceeding the current threshold Th by the coefficient α=0.4 is set as the new threshold Th′, the standard index Assuming that the peak value of the value b is p, the updated threshold Th' in the normal state is about Th'=p×α=p×0.4. If abnormal noise with a peak value of X occurs once, the next threshold Th' increases by (Xp)/5*0.4=0.08X-0.2Th. If X=5000 μV, then 400−0.2 Th [μV]. In other words, when the sampling interval is 5 ms, there is a high probability that noise is influencing when the amount of increase in the next threshold Th' from the current threshold Th exceeds 400-0.2 Th [μV].

Therefore, in this embodiment, when the threshold candidate Thc calculated in step S22 exceeds the threshold limit value L = 400 + 0.8 Th [μV] (= Th + 400 - 0.2 Th) with respect to the current threshold Th, ( YES in step S23), the threshold value Th should not be updated. A general formula for the threshold limit value L is as follows.
L=Th+(α/V)X−(1/V)Th (5)

As described above, the threshold Th is set based on the value obtained by multiplying the value of the peak to be detected by a coefficient α of 1 or less. In the method of adaptively updating the threshold Th, when the input signal level decreases and the peaks of the index value b with small amplitude continue, the threshold Th decreases. In a situation where the threshold Th is unbelievably low as a threshold Th derived from a human ECG waveform, even if there is a peak in the index value b, the probability that this peak is derived from the R wave is low.

With the method of restricting the threshold Th so that it does not fall below the lower limit, it is possible to prevent the detection of a peak with a small amplitude of the index value b, but it reacts to the index value b exceeding the threshold Th. Therefore, even a peak of the index value b that is derived from noise or the like added to the ECG waveform is detected as a heartbeat.

On the other hand, in the present embodiment, when the threshold value Th is less than the lower limit value Thmin, the heartbeat determination (step S10) is not performed. detection can be achieved.
Note that the threshold update method described with reference to FIG. 3 is an example, and the threshold may be updated by another method.

The storage unit 2, the positive/negative inversion value calculation unit 3, the maximum value detection unit 4, the index value calculation unit 5, the threshold determination unit 6, the heartbeat time determination unit 7, and the threshold value setting unit 8 of the heartbeat detection apparatus described in this embodiment are , a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. A configuration example of this computer is shown in FIG.

The computer comprises a CPU 200 , a storage device 201 and an interface device (I/F) 202 . The I/F 202 is connected to the electrocardiograph 1 and the like. A program for implementing the heartbeat detection method of the present invention is stored in the storage device 201 . The CPU 200 executes the processing described in this embodiment according to the programs stored in the storage device 201 .

The present invention can be applied to technology for detecting the heartbeat of a living body.

DESCRIPTION OF SYMBOLS 1... Electrocardiograph, 2... Storage part, 3... Positive/negative inversion value calculation part, 4... Maximum value detection part, 5... Index value calculation part, 6... Threshold determination part, 7... Heartbeat time determination part, 8... Threshold value setting Sections 40 to 42, 50... FIFO buffer, 43... Detection processing section, 51... Subtraction processing section.

Claims

a first step of calculating an index value from a sampled data string of an electrocardiogram waveform of a living body at each sampling time;
a second step of comparing a threshold for heartbeat detection with a lower limit of a plausible range for the threshold derived from a biological electrocardiogram waveform;
a third step in which when the threshold is determined to be equal to or greater than the lower limit in the second step and a peak of the index value exceeding the threshold is detected, the sampling time of the peak is set to the heartbeat time;
A heartbeat detection method, wherein when the second step determines that the threshold is less than the lower limit, heartbeat detection is not performed by comparing the threshold and the index value.
The heart rate detection method of claim 1, wherein
a fourth step of calculating, at each sampling time, the positive/negative inversion value of the time difference of the sampled data from the sampled data string of the electrocardiogram waveform;
The maximum value of the positive/negative inverted value within a certain time range before the sampling time to be processed and the positive/negative inverted value within a certain time range after the sampling time to be processed is detected at each sampling time. a fifth step;
The heartbeat detection method, wherein the first step includes a step of calculating, at each sampling time, a subtraction value obtained by subtracting the maximum value from the positive/negative inversion value of the sampling time to be processed as the index value.
The heartbeat detection method according to claim 1 or 2,
A heartbeat detection method, further comprising a sixth step of updating the threshold based on peaks in the index value that exceed a current threshold.
an index value calculation unit configured to calculate an index value at each sampling time from a sampled data string of an electrocardiogram waveform of a living body;
a threshold determination unit configured to compare a threshold for heartbeat detection with a lower limit of a plausible range as the threshold derived from an electrocardiogram waveform of a living body;
A heartbeat time determination unit configured to set a sampling time of the peak as a heartbeat time when the threshold is determined to be equal to or greater than the lower limit value by the threshold determination unit and a peak of the index value exceeding the threshold is detected. and
The heartbeat detection device, wherein the heartbeat time determination unit does not perform heartbeat detection by comparing the threshold value and the index value when the threshold value is determined to be less than the lower limit value.
The heartbeat detection device of claim 4, wherein
a positive/negative inverted value calculation unit configured to calculate, at each sampling time, a positive/negative inverted value of the time difference of the sampling data from the sampled data string of the electrocardiogram waveform;
The maximum value of the positive/negative inverted value within a certain time range before the sampling time to be processed and the positive/negative inverted value within a certain time range after the sampling time to be processed is detected at each sampling time. further comprising a maximum value detection unit configured to
The heartbeat detection device, wherein the index value calculation unit calculates a subtraction value obtained by subtracting the maximum value from the positive/negative inversion value of the sampling time to be processed as the index value at each sampling time.
The heartbeat detection device according to claim 4 or 5,
The heart rate detection device, further comprising a threshold setting unit configured to update the threshold based on peaks of the index value exceeding a current threshold.