JP7632659B2 - Heart rate detection method and heart rate detection device - Google Patents

Description

The present invention relates to a heart rate detection method and a heart rate detection device for detecting heart rate from an electrocardiogram waveform.

An ECG (Electrocardiogram) waveform is a measurement of the electrical activity of the heart, and consists of a series of heartbeat waveforms. A single heartbeat waveform is made up of components such as P waves, Q waves, R waves, S waves, and T waves, which reflect the activity of the atria and ventricles. Of these, the R wave is associated with ventricular contraction and has a large amplitude, so heartbeats are often detected based on peaks derived from the R wave.

A conventional heart rate detection method is disclosed in Patent Document 1. The method disclosed in Patent Document 1 uses an index value that focuses on the relationship between the peak of the time difference value of the ECG waveform and the values in a certain time region before and after it, and detects R-waves using a judgment logic based on a threshold. This method has the advantage that it is sensitive not only to the amplitude but also to the shape (time width of the peak) of the ECG waveform, and can emphasize peaks that are likely to be R-waves.

On the other hand, when detecting R-waves using threshold-based decision logic, it is normal for the index value to continue exceeding the threshold for a while even after it has exceeded the threshold once. Also, because there is an upper limit to a person's heart rate, it is reasonable to assume that the next R-wave will not arrive immediately after an R-wave. Therefore, it is common practice to stop R-wave detection for a certain period of time after detecting an R-wave.

In addition, if the R-R interval (RRI), which is the time interval between a detected R wave and the previous R wave, is shorter than the standard, it is reasonable to determine that noise other than an R wave has been mistakenly detected and reject the R wave detection. In addition, in R wave detection, errors such as noise mixed into the ECG waveform can cause the instantaneous heart rate (= 60,000/RRI) to deviate from the normal value. For this reason, it is common to apply a time-averaging process to the instantaneous heart rate to output a stabilized average heart rate.

However, ECG waveforms vary from person to person, and depending on the shapes of the Q, R, and S waves, the peak of the index value as described above may be gentle, or the index value may have multiple peaks. For this reason, the timing at which it is determined that the index value has exceeded the threshold may fluctuate back and forth by up to about 20 ms. This fluctuation in timing, the setting of the lower limit of the RRI, and the skipping process of R-wave detection may cause errors in detecting R-waves and measuring the heart rate.

The reasons for the errors in R-wave detection and heart rate measurement are explained below. Figures 8 and 9 are diagrams showing examples of index values calculated by a conventional heart rate detection method. However, only the index values near the threshold value TH are shown. Here, we consider a case where the upper limit of the heart rate to be measured is 300 bpm, and the heart rate obtained from the observed ECG waveform is also 300 bpm. Two consecutive peaks P1 and P2 appear in the index value. The centers of peaks P1 and P2 are separated by an RRI of 200 ms, which corresponds to a heart rate of 300 bpm. The tips of peaks P1 and P2 are not sharp, but have a gently wavy shape.

In the example of Figure 8, the index value exceeds the threshold value TH at time T1, and so time T1 is detected as the time of an R wave. The index value next exceeds the threshold value TH at time T2, and the interval between times T1 and T2 is 186 ms. However, the skip width tskip after R-wave detection is set to 200 ms, and R-wave detection is temporarily halted during the period up to 200 ms after time T1, so time T2 cannot be detected as the time of an R wave.

In the example of Fig. 9, the skip width tskip is changed to 180 ms. As in the example of Fig. 8, the index value exceeds the threshold value TH at time T1, so that time T1 is detected as the time of an R wave. Furthermore, after the elapsed time from time T1 exceeds tskip = 180 ms, the index value exceeds the threshold value TH at time T2, so that time T2 is detected as the time of an R wave. However, since the lower limit value RRI _LOW is set to 200 ms and the interval between times T1 and T2 is 186 ms, 186 ms is not adopted as the RRI and is excluded from the calculation of the instantaneous heart rate. In addition, the next time the index value exceeds the threshold value TH is time T3, but since R-wave detection is temporarily suspended during the period from time T2 until 180 ms, time T3 passes without being detected as the time of an R wave.

8 and 9, even if there is fluctuation in the timing at which the index value exceeds the threshold value TH, if each peak is detected without missing, the RRI can be averaged to a constant value even if the instantaneous RRI value fluctuates, and an appropriate average heart rate can be obtained. However, if the lower limit of the RRI is set too tightly to match the upper limit of the heart rate to be measured, as in the example of Figure 9, cases where the RRI is on the short side will be excluded, and the average heart rate calculated will be biased toward the lower side than the actual one.

Patent No. 6527286

The present invention has been made to solve the above problems, and aims to provide a heart rate detection method and a heart rate detection device that can accurately measure heart rate.

The heart rate detection method of the present invention includes a first step of detecting an R wave from an electrocardiogram waveform of a living body, a second step of calculating an R-R interval, which is the time interval between the R wave detected in the first step and the immediately preceding R wave, and a third step of calculating a heart rate based on the R-R interval, wherein the first step includes a step of stopping R-wave detection during a period in which the elapsed time from the time of the latest R wave is equal to or less than a skip width, and the skip width is set to a value shorter than 60000/HRmax when an upper limit value of the heart rate to be measured is HRmax, and the second step includes a step of not adopting the calculated time as the R-R interval when the time obtained by subtracting the time of the immediately preceding R wave from the time of the latest R wave detected in the first step is shorter than a lower limit value, and the lower limit value is set to a value shorter than 60000/HRmax when an upper limit value of the heart rate to be measured is HRmax.

In one configuration example of the heart rate detection method of the present invention, the skip width is set to a value shorter than (60000/HRmax)-20.
In one configuration example of the heart rate detection method of the present invention, the lower limit is set to a value shorter than (60000/HRmax)-20.
In one configuration example of the heart rate detection method of the present invention, the skip width is equal to or smaller than the lower limit value.

The heart rate detection device of the present invention includes an R-wave detection unit configured to detect R-waves from an electrocardiogram waveform of a living body, an R-R interval calculation unit configured to calculate an R-R interval, which is the time interval between an R wave detected by the R-wave detection unit and the immediately previous R wave, and a heart rate calculation unit configured to calculate a heart rate based on the R-R interval, wherein the R-wave detection unit stops R-wave detection during a period in which the elapsed time from the time of the latest R wave is equal to or less than a skip width, and the skip width is set to a value shorter than 60,000/HRmax when an upper limit value of the heart rate to be measured is HRmax , and the R-R interval calculation unit does not adopt the calculated time as the R-R interval when the time obtained by subtracting the time of the immediately previous R wave from the time of the latest R wave detected by the R-wave detection unit is shorter than a lower limit value, and the lower limit value is set to a value shorter than 60,000/HRmax when an upper limit value of the heart rate to be measured is HRmax.

According to the present invention, by setting the skip width to a value shorter than 60,000/HRmax for the upper limit value HRmax of the heart rate to be measured, R waves can be detected without missing any, and the heart rate can be measured accurately.

FIG. 1 is a block diagram showing the configuration of a heart rate detection device according to an embodiment of the present invention. FIG. 2 is a flowchart illustrating the operation of the heart rate detection device according to the embodiment of the present invention. FIG. 3 is a block diagram showing the configuration of an R wave detection unit of the heart rate detection device according to the embodiment of the present invention. FIG. 4 is a flowchart illustrating the operation of the R wave detection unit of the heart rate detection device according to the embodiment of the present invention. FIG. 5 is a diagram illustrating an example of the operation of the heart rate detection device according to the embodiment of the present invention. FIG. 6 is a diagram illustrating an example of the operation of the heart rate detection device according to the embodiment of the present invention. FIG. 7 is a block diagram showing an example of the configuration of a computer that realizes a heartbeat detection device according to an embodiment of the present invention. FIG. 8 is a diagram for explaining a conventional heartbeat detection method. FIG. 9 is a diagram for explaining a conventional heartbeat detection method.

An embodiment of the present invention will now 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 present invention. The heartbeat detection device includes an electrocardiograph 1 that outputs a sampling data string of an ECG waveform, a memory unit 2 that stores the sampling data string of the ECG waveform and information on the sampling time, an R-wave detection unit 3 that detects R-waves from the sampling data string of the ECG waveform, an R-R interval calculation unit 4 that calculates the R-R interval from time series data of the R-wave times, and a heart rate calculation unit 5 that calculates the heart rate based on the R-R interval.

Next, the operation of the heart rate detection device of this embodiment will be explained with reference to Figure 2. In this embodiment, the data string obtained by sampling the ECG waveform is designated as D(i). i (i = 1, 2, ...) is a number assigned to one sample of data. It goes without saying that the larger the number i, the later the sampling time.

The electrocardiograph 1 measures the ECG waveform of a living body (human body) (not shown) and outputs a sampling data sequence D(i) of the ECG waveform (step S1 in FIG. 2). At this time, the electrocardiograph 1 outputs each sampling data by adding information on the sampling time. Since the specific method of measuring the ECG waveform is a well-known technique, a detailed explanation is omitted. The memory 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.

The R wave detection unit 3 detects R waves from the sampling data sequence D(i) of the ECG waveform stored in the memory unit 2 (step S2 in Figure 2).

3 is a block diagram showing the configuration of the R-wave detection unit 3. The R-wave detection unit 3 includes a positive/negative inversion value calculation unit 30 that calculates the positive/negative inversion value of the time difference of the sampling data from the sampling data string of the ECG waveform for each sampling time, a maximum value detection unit 31 that detects the maximum value of the positive/negative inversion value of the time difference of the time range A before the sampling time to be processed and the positive/negative inversion value of the time difference of the time range B after the sampling time to be processed for each sampling time, an index value calculation unit 32 that calculates an index value for each sampling time by subtracting the maximum value from the positive/negative inversion value of the time difference of the sampling time to be processed, and a time determination unit 33 that sets the sampling time to be processed as the time of the R wave when the index value exceeds a predetermined threshold value.

The maximum value detection unit 31 is composed of a FIFO buffer (First In, First Out) 310 which receives as input the time difference positive/negative inversion value calculated by the positive/negative inversion value calculation unit 30, a FIFO buffer 311 which receives as input the output value of the FIFO buffer 310, a FIFO buffer 312 which receives as input the output value of the FIFO buffer 311, and a detection processing unit 313 which detects the maximum value M of the time difference positive/negative inversion value stored in the FIFO buffer 310 and the time difference positive/negative inversion value stored in the FIFO buffer 312 for each sampling time.

The index value calculation unit 32 is composed of a FIFO buffer 320 which receives as input the time difference positive/negative inversion value calculated by the positive/negative inversion value calculation unit 30, and a subtraction processing unit 321 which calculates an index value x for each sampling time by subtracting the maximum value M detected by the maximum value detection unit 31 from the output value of the FIFO buffer 320.

The operation of the R-wave detection unit 3 of this embodiment will be described below with reference to Fig. 4. 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 30 acquires data D(i+1) one sampling after the sampling data D(i) and data D(i-1) one sampling before the sampling data D(i) from the storage unit 2 (step S100 in Fig. 4). Then, the positive/negative inversion value calculation unit 30 calculates the time difference positive/negative inversion value Y(i) of the sampling data D(i) for each sampling time as follows (step S101 in Fig. 4).
Y(i)=-{D(i+1)-D(i-1)} ...(1)

The positive/negative inversion value calculation unit 30 inputs the calculated time difference positive/negative inversion value Y(i) to the FIFO buffer 320 for each sampling time (step S102 in Figure 4).

The positive/negative inversion value calculation unit 30 also inputs the calculated time difference positive/negative inversion value Y(i) to FIFO buffer 310 for each sampling time (step S103 in FIG. 4). The output of FIFO buffer 310 is input to FIFO buffer 311 (step S104 in FIG. 4), and the output of FIFO buffer 311 is input to FIFO buffer 312 (step S105 in FIG. 4). FIFO buffers 310 to 312 are used to find the maximum value M of the time difference positive/negative inversion value in the time ranges A and B.

The time interval L3 corresponding to the length of the FIFO buffer 311 (the delay time from when the time difference positive/negative inversion value is input to the FIFO buffer 311 until it is output) needs to be sufficiently wide compared to the width of the R-wave-derived peak (approximately 10 ms), and is preferably about 50 ms. This interval L3 is the interval between time ranges A and B. In addition, the time interval L2 corresponding to the length of the FIFO buffer 310 (the delay time from when the time difference positive/negative inversion value is input to the FIFO buffer 310 until it is output) and the time interval L4 corresponding to the length of the FIFO buffer 312 (the delay time from when the time difference positive/negative inversion value is input to the FIFO buffer 312 until it is output, L2=L4) are appropriately about 100 ms.

The time interval L1, which corresponds to the length of the FIFO buffer 320, can be set as L1 = L2 + L3/2. Therefore, in the above numerical example, L1 is 125 ms. By setting L1 = L2 + L3/2 and L2 = L4, it is possible to find the maximum value M for the ranges of -(L2 + L3/2) to -(L3/2) and (L3/2) to (L2 + L3/2) for the time of the output value a of the FIFO buffer 320 (the sampling time to be processed), and it is possible to subtract the maximum value M from the output value a.

The detection processing unit 313 detects the maximum value M of the positive/negative inverted time difference values stored in the FIFO buffer 310 and the positive/negative inverted time difference values stored in the FIFO buffer 312 for each sampling time (step S106 in FIG. 4).
The subtraction processing unit 321 calculates an index value x(i)=a−M by subtracting the maximum value M from the output value a of the FIFO buffer 320 for each sampling time (step S107 in FIG. 4).

When the index value x(i) exceeds a predetermined threshold TH (YES in step S108 in FIG. 4), the time determination unit 33 determines whether the sampling time of the index value x(i) is appropriate as the time of the R wave, and determines the time of the R wave. Specifically, the time determination unit 33 determines whether the time difference ΔT between the sampling time of the index value x(i) that exceeds the threshold TH and the time of the R wave determined immediately before is longer than a preset skip width tskip (step S109 in FIG. 4), and if the time difference ΔT is equal to or less than the skip width tskip (NO in step S109), the sampling time of the index value x(i) that exceeds the threshold TH is not adopted as the time of the R wave. By the processing of step S109 in this manner, the skip processing of the R wave detection can be realized. If the sampling time of the index value x(i) is not adopted as the time of the R wave, the processing target is shifted to the sampling data D(i) of the next sampling time, and the processing from step S100 onwards is performed again.

In addition, if the time difference ΔT is longer than the skip width tskip (YES in step S109), the time determination unit 33 determines the sampling time of the index value x(i) that exceeds the threshold value TH as the time of the R wave (step S110 in Figure 4).

As described above, the time difference positive/negative inversion value Y(i) is calculated from the sampling data D(i), and the index value x(i) is calculated from the time difference positive/negative inversion value Y(i). Therefore, the sampling time of the index value x(i) is the sampling time of the time difference positive/negative inversion value Y(i) (the sampling time of the data D(i)), and can be obtained from the memory unit 2.

In this manner, the process of steps S100 to S110 is repeatedly executed for each sampling period to obtain time series data of the R-wave times. The time series data of the detected R-wave times is stored in the storage unit 2.
The above-described method for detecting R waves is merely an example, and R waves may be detected by other methods.

In this embodiment, the skip width tskip is set to be equal to or less than the lower limit of the R-R interval (RRI). When the upper limit of the instantaneous heart rate to be measured is HRmax [bpm], the lower limit of the RRI RRI _LOW is greater than 0 and less than (60000/HRmax) [ms]. More specifically, the lower limit of the RRI RRI _LOW is set to a value greater than 0 and less than ((60000/HRmax)-20) [ms]. The assumed upper limit of the instantaneous heart rate HRmax is, for example, 300 bpm.

Therefore, the skip width tskip is greater than 0 and less than (60000/HRmax) [ms]. More specifically, the skip width tskip is set to a value greater than 0 and less than ((60000/HRmax)-20) [ms].

Next, the R-R interval calculation unit 4 calculates the time d by subtracting the time of the immediately preceding R wave from the time of the latest R wave detected by the R wave detection unit 3 (step S3 in FIG. 2). If the calculated time d is shorter than a preset lower limit value RRI _{LOW (NO in FIG. 2, step S4), the R-R interval calculation unit 4 discards the time d without adopting it as the RRI. On the other hand, if the time d is equal to or greater than the lower limit value RRI LOW (} YES in step S4), the R-R interval calculation unit 4 determines the time d as the RRI [ms] (step S5 in FIG. 2).

The heart rate calculation unit 5 calculates an instantaneous heart rate HR(i) [bpm] for each RRI based on the RRI [ms] calculated by the RR interval calculation unit 4 (step S6 in FIG. 2).
HR(i)=60000/RRI...(2)

The heart rate calculation unit 5 also calculates an average heart rate HRave(i) [bpm] for each RRI (step S7 in FIG. 2). As described above, the instantaneous heart rate calculated from the i-th RRI(i) before averaging is HR(i), the average value of the instantaneous heart rates up to the i-1th is HRave(i-1), and a predetermined averaging coefficient is r. Then, the average value HRave(i) of the instantaneous heart rates up to the i-th can be calculated by the following formula (3).
HRave(i)=r×HR(i)+(1-r)×HRave(i-1)
...(3)

In this way, by repeating the processes of steps S1 to S7, time series data of the instantaneous heart rate HR(i) and the average heart rate HRave(i) are obtained. The calculated time series data is stored in the memory unit 2.

Figure 5 shows an example in which the heart rate detection method according to this embodiment is applied to the example of Figure 8. Here, the skip width tskip is 180 ms. In the example of Figure 5, the index value x exceeds the threshold value TH at time T1, so the R-wave detection unit 3 detects time T1 as the time of an R-wave. The R-wave detection unit 3 temporarily suspends R-wave detection during the period from time T1 until tskip = 180 ms, but because the index value x exceeds the threshold value TH 186 ms after time T1, it detects time T2 as the time of an R-wave. In this way, in this embodiment, the time T2 at which the index value x exceeds the threshold value TH can be properly detected.

Fig. 6 shows an example in which the heartbeat detection method according to this embodiment is applied to the example in Fig. 9. Here, the skip width tskip and the lower limit value RRI _LOW are both set to 180 ms. As in the example in Fig. 5, the index value exceeds the threshold value TH at time T1, so that the R-wave detection unit 3 detects time T1 as the time of an R-wave. Furthermore, after the elapsed time from time T1 exceeds tskip = 180 ms, the index value exceeds the threshold value TH at time T2, so that the R-wave detection unit 3 detects time T2 as the time of an R-wave.

Since the time d=186 ms obtained by subtracting time T1 from time T2 is equal to or greater than the lower limit value RRI _LOW =180 ms of the RRI, the R-R interval calculation unit 4 adopts the time d as the RRI. In this way, in this embodiment, the RRI can be detected appropriately. In addition, since the peak of the index value x can be detected without missing it, the average heart rate can also be calculated appropriately.

The memory unit 2, R wave detection unit 3, R-R interval calculation unit 4, and heart rate calculation unit 5 of the heart rate detection device described in this embodiment can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in Figure 7.

The computer comprises a CPU 100, a storage device 101, and an interface device (I/F) 102. An electrocardiograph 1 and the like are connected to the I/F 102. A program for implementing the heart rate detection method of the present invention is stored in the storage device 101. The CPU 100 executes the processing described in this embodiment in accordance with the program stored in the storage device 101.

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

1...electrocardiograph, 2...memory unit, 3...R wave detection unit, 4...R-R interval calculation unit, 5...heart rate calculation unit, 30...positive/negative inversion value calculation unit, 31...maximum value detection unit, 32...index value calculation unit, 33...time determination unit, 310-312, 320...FIFO buffer, 313...detection processing unit, 321...subtraction processing unit.

Claims (6)

A first step of detecting an R wave from an electrocardiogram waveform of a living body;
A second step of calculating an R-R interval, which is a time interval between the R wave detected in the first step and the immediately preceding R wave;
and a third step of calculating a heart rate based on the R-R interval.
the first step includes a step of stopping R-wave detection during a period in which an elapsed time from a time of the latest R-wave is equal to or less than a skip width;
The skip width is set to a value shorter than 60000/HRmax , where HRmax is the upper limit of the heart rate to be measured.
the second step includes a step of not adopting the calculated time as the R-R interval when the time obtained by subtracting the time of the immediately preceding R wave from the time of the latest R wave detected in the first step is shorter than a lower limit value;
The heart rate detection method according to the present invention is characterized in that the lower limit is set to a value shorter than 60,000/HRmax, where HRmax is an upper limit value of the heart rate to be measured . 2. The method for detecting a heartbeat according to claim 1 ,
A heartbeat detection method, characterized in that the skip width is set to a value shorter than (60000/HRmax)-20. 2. The method for detecting a heartbeat according to claim 1 ,
The heart rate detection method according to the present invention, wherein the lower limit is set to a value shorter than (60000/HRmax)-20. 4. The heartbeat detection method according to claim 1 , further comprising:
A heartbeat detection method, wherein the skip width is equal to or smaller than the lower limit value. An R wave detection unit configured to detect an R wave from an electrocardiogram waveform of a living body;
an R-R interval calculation unit configured to calculate an R-R interval, which is a time interval between an R wave detected by the R wave detection unit and the immediately preceding R wave;
a heart rate calculation unit configured to calculate a heart rate based on the R-R interval,
The R wave detection unit stops R wave detection during a period in which an elapsed time from the time of the latest R wave is equal to or less than a skip width,
The skip width is set to a value shorter than 60000/HRmax , where HRmax is the upper limit of the heart rate to be measured.
the R-R interval calculation unit, when a time obtained by subtracting a time of the immediately preceding R wave from a time of the latest R wave detected by the R wave detection unit is shorter than a lower limit value, does not adopt the calculated time as the R-R interval,
A heart rate detection device according to claim 1, wherein the lower limit is set to a value shorter than 60,000/HRmax, where HRmax is an upper limit value of the heart rate to be measured . 6. The heartbeat detection device according to claim 5 ,
A heart rate detection device, wherein the skip width is equal to or smaller than the lower limit value.

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