JP7589826B2 - 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 a heart rate (R wave) 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 can be sensitive not only to the amplitude but also to the shape (time width) of the ECG waveform, and that T-waves, which are wider than R-waves, are less likely to be mistaken for R-waves.

Figure 14 shows an example of an ECG waveform. The ECG waveform contains one heartbeat. The amplitude (peak to valley) of the cardiac potential is approximately 500 μV, which is smaller than the usual value (2000 to 3000 μV), but the amplitude may attenuate depending on the position and condition of the electrodes detecting the cardiac potential.

Figure 15 shows the time difference of the ECG waveforms in Figure 14, with the positive and negative values inverted. By taking the time difference of the ECG waveforms, it can be seen that the upward peaks associated with the steep drop in cardiac potential from the R wave to the S wave appear in line with the rhythm of the heartbeat.

The index value obtained by subtracting the maximum value of the positive and negative inverted time difference values in certain time ranges A and B around time t in Figure 15 from the positive and negative inverted time difference value at time t corresponds to the height of the peak clearance around time t. This index value becomes negative for times outside the peak.

Figure 16 is a plot of time series data of index values. According to Figure 16, the index values have peaks with a time width smaller than the interval between time ranges A and B emphasized. When the detection target is R waves, it is preferable to set time ranges A and B to 100 ms and the interval between time ranges A and B to 50 ms, for example. As shown in Figure 16, R waves can be detected by applying a judgment logic based on a threshold value TH to the index values. The threshold value TH can be obtained by a method such as finding the maximum value of the index values in a period including multiple heartbeat-derived peaks and multiplying this maximum value by a coefficient of 1 or less.

However, when using the above-mentioned index values, there was a possibility that waveforms that were too short in duration and therefore considered inappropriate for R waves would be mistakenly recognized as R waves.

Patent No. 6527286

The present invention has been made to solve the above problem, and aims to provide a heart rate detection method and a heart rate detection device that do not mistakenly recognize peaks with too short a time width as heart rates.

The heartbeat detection method of the present invention includes a first step of calculating a positive/negative inversion value of a time difference of sampling data from a sampling data sequence of an electrocardiogram waveform of a living body for each sampling time; a second step of detecting, for each sampling time, a first maximum value of the positive/negative inversion value in a first time range prior to the sampling time of the processing target and the positive/negative inversion value in a second time range after the sampling time of the processing target; a third step of detecting, for each sampling time, a second maximum value of the positive/negative inversion value in a third time range prior to the sampling time of the processing target and the positive/negative inversion value in a fourth time range after the sampling time of the processing target; a fourth step of calculating, for each sampling time, a subtraction value obtained by subtracting the first maximum value from the positive/negative inversion value at the sampling time of the subject as a first index value; a fifth step of calculating, for each sampling time, a subtraction value obtained by subtracting the second maximum value from the positive/negative inversion value at the sampling time of the subject to be processed as a second index value; and a sixth step of setting the first sampling time as the heartbeat time when the second index value at the first sampling time at which the first index value exceeds a predetermined threshold value and the first index value at a second sampling time having a predetermined relationship with the first sampling time satisfy a predetermined condition.

Furthermore, in one configuration example of the heart rate detection method of the present invention, the timing of the leading edge of the third time range relative to the sampling time of the processing object is the same as the timing of the leading edge of the first time range, the timing of the trailing edge of the fourth time range relative to the sampling time of the processing object is the same as the timing of the trailing edge of the second time range, and the interval between the third time range and the fourth time range is shorter than the interval between the first time range and the second time range.
Furthermore, in one configuration example of the heartbeat detection method of the present invention, the sixth step is characterized in including a step of setting the first sampling time as the heartbeat time when the first index value at the first sampling time increases relative to the first index value prior to the first sampling time, and when the second index value at the first sampling time and the first index value at the second sampling time satisfy a predetermined condition.
In one configuration example of the heartbeat detection method of the present invention, the interval between the third time range and the fourth time range is in the range of 20 ms to 30 ms.

The heartbeat detection device of the present invention further comprises a positive/negative inversion value calculation unit configured to calculate a positive/negative inversion value of a time difference of sampling data from a sampling data sequence of an electrocardiogram waveform of a living body for each sampling time, a first maximum value detection unit configured to detect, for each sampling time, a first maximum value among the positive/negative inversion value in a first time range prior to the sampling time of the processing target and the positive/negative inversion value in a second time range after the sampling time of the processing target, and a second maximum value detection unit configured to detect, for each sampling time, the positive/negative inversion value in a third time range prior to the sampling time of the processing target and the second maximum value among the positive/negative inversion value in a fourth time range after the sampling time of the processing target, and a first index value calculation unit configured to calculate, for each sampling time, a subtraction value obtained by subtracting the first maximum value from the positive/negative inversion value at the sampling time of the processing target as a first index value; a second index value calculation unit configured to calculate, for each sampling time, a subtraction value obtained by subtracting the second maximum value from the positive/negative inversion value at the sampling time of the processing target as a second index value; and a heartbeat time determination unit configured to determine the first sampling time as the heartbeat time when the second index value at the first sampling time at which the first index value exceeds a predetermined threshold and the first index value at a second sampling time having a predetermined relationship with the first sampling time satisfy a predetermined condition.

In addition, in one configuration example of the heart rate detection device of the present invention, the timing of the leading edge of the third time range relative to the sampling time of the processing object is the same as the timing of the leading edge of the first time range, the timing of the trailing edge of the fourth time range relative to the sampling time of the processing object is the same as the timing of the trailing edge of the second time range, and the interval between the third time range and the fourth time range is shorter than the interval between the first time range and the second time range.
Furthermore, in one configuration example of the heartbeat detection device of the present invention, the heartbeat time determination unit determines the first sampling time as the heartbeat time when the first index value at the first sampling time increases relative to the first index value prior to the first sampling time, and the second index value at the first sampling time and the first index value at the second sampling time satisfy a predetermined condition.
In one configuration example of the heartbeat detection device of the present invention, the interval between the third time range and the fourth time range is in the range of 20 ms to 30 ms.

According to the present invention, a first index value is calculated by subtracting the maximum value of the positive and negative inversion of the time difference in the first and second time ranges before and after the sampling time to be processed from the positive and negative inversion of the time difference at the sampling time to be processed, and a second index value is calculated by subtracting the maximum value of the positive and negative inversion of the time difference in the third and fourth time ranges before and after the sampling time to be processed from the positive and negative inversion of the time difference at the sampling time to be processed. When the second index value at the first sampling time at which the first index value exceeds a threshold value and the first index value at the second sampling time that has a predetermined relationship with the first sampling time satisfy a predetermined condition, the first sampling time is set as the heartbeat time. As a result, in the present invention, it is possible to detect a peak of an index value that is likely to be an R wave, and to exclude a peak of an index value that is too short in time width and has low reliability as an R wave, thereby enabling accurate heartbeat detection.

FIG. 1 is a diagram showing positive and negative inversion values of the time difference of an ECG waveform. FIG. 2 is a diagram showing time series data of the first index value and the second index value of an ECG waveform. FIG. 3 is an enlarged view of FIG. FIG. 4 is a diagram showing an example of a pseudo waveform that imitates an ECG waveform. FIG. 5 is a diagram showing time-series data of the first index value and the second index value of the pseudo waveform. 6A to 6C are diagrams showing time-series data of the first index value and the second index value of an ECG waveform. 7A to 7C are diagrams showing time-series data of the first index value and the second index value of the pseudo waveform. FIG. 8 is a block diagram showing the configuration of a heart rate detection device according to an embodiment of the present invention. FIG. 9 is a block diagram showing an example of the configuration of a maximum value detection unit, an index value calculation unit, and an index value storage unit of a heart rate detection device according to an embodiment of the present invention. FIG. 10 is a flow chart illustrating a heart rate detection method according to an embodiment of the present invention. FIG. 11 is a flowchart illustrating a method for calculating the first index value. FIG. 12 is a flowchart illustrating a method for calculating the second index value. FIG. 13 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. 14 is a diagram showing an example of an ECG waveform. FIG. 15 is a diagram showing the time difference positive/negative inversion values of the ECG waveform of FIG. FIG. 16 is a diagram showing time-series data of index values calculated by a conventional heartbeat detection method.

[Principle of the Invention]
FIG. 1 shows the positive/negative inverted time difference values of the same ECG waveform as in FIG. 15. The difference from FIG. 15 is that second time ranges C and D are also shown. The timing of the leading edge of time range C relative to the sampling time to be processed (t in the example of FIG. 1) is the same as the timing of the leading edge of time range A. Also, the timing of the trailing edge of time range D relative to the sampling time to be processed is the same as the timing of the trailing edge of time range B. Meanwhile, the interval between time ranges C and D is shorter than the interval between time ranges A and B. In the examples of FIG. 2 to FIG. 4 below, the interval between time ranges C and D is 24 ms.

The positive and negative inverted time difference value of the ECG waveform is calculated for each sampling time. The first index value x of the sampling time is determined by subtracting the maximum value M1 of the positive and negative inverted time difference value of time range A before the sampling time to be processed and the positive and negative inverted time difference value of time range B after the sampling time to be processed from the positive and negative inverted time difference value of the sampling time to be processed. The second index value y of the sampling time is determined by subtracting the maximum value M2 of the positive and negative inverted time difference value of time range C before the sampling time to be processed and the positive and negative inverted time difference value of time range D after the sampling time to be processed from the positive and negative inverted time difference value of the sampling time to be processed.

Figure 2 is a plot of time series data of the first index value x and the second index value y of the ECG waveform in Figure 14. It can be seen that the peak of the second index value y is narrower than the peak of the first index value x.

Figure 3 shows an enlarged view of the area around the peak derived from the R wave in Figure 2. In Figure 3, values are plotted for each sampling interval of 1 ms. It can be seen that the first index value x and the second index value y diverge as they move away from the apex of the peak. The reason that the first index value x and the second index value y diverge is that as the time shifts away from the center of the peak, the trailing edge of time range C and the leading edge of time range D interfere with the peak of the time difference positive/negative inversion value of the ECG waveform, causing the maximum value M2 in time ranges C and D to rise and the slope of the base of the peak of the second index value y to become steeper.

On the other hand, Figure 4 shows an example of a pseudo waveform that imitates an ECG waveform. The waveform shown in Figure 4 has the time widths of the Q wave, R wave, and S wave shortened to about half, and shows an example that should not be detected as an R wave.

Figure 5 shows a plot similar to that of Figure 3 for the waveform of Figure 4. Compared to Figure 3, there is less deviation between the first index value x and the second index value y. The reason for the small deviation between the first index value x and the second index value y is that the width of the peak is narrower compared to the interval between time ranges C and D, there is less interference between time ranges C and D and the peak waveform, and an increase in the maximum value M2 as in the case of Figure 3 is less likely to occur.

Comparing Figures 3 and 5, in Figure 3 the difference between the first index value x and the second index value y gradually increases as one moves away from the peak, while in Figure 5 the difference between the first index value x and the second index value y is smaller than in Figure 3. To utilize such a relationship between the first index value x and the second index value y for R-wave detection, it is advisable to focus on the relationship between the second index value y at a certain point in time and the first index value x at a slightly distant point in time.

In Figure 3, the first index value x = x3 exceeds the threshold value TH at time t3. For example, if the second index value y = y3 at the same time t3 and the first index value x = x1 at the time two samples before that satisfy the condition (x1 - y3) > a (a is a predetermined positive value), then time t3 can be determined as the heartbeat time. In other words, the upward peak that appears immediately after time t3 can be detected as a peak derived from an R wave.

Under the same conditions, in the case of Figure 5, the first index value x = x3 is lower than the second index value y = y1, so time t3 is not detected as a heart beat time and the peak in Figure 5 is not detected as a peak derived from an R wave.

Note that the above condition may be satisfied when the first index value x and the second index value y pass the peak and fall. In order to prevent the condition from being satisfied when the first index value x and the second index value y fall, a further condition that the first index value x is increasing (x3>x2) at time t3 is imposed, so that the peak in FIG. 5 is not detected as an R-wave-derived peak.

Figures 6A to 6C are plots of time series data of the first index value x and second index value y of the ECG waveform in Figure 14. Figures 7A to 7C are plots of time series data of the first index value x and second index value y of the pseudo waveform in Figure 4. Figures 6A and 7A show the case where the interval between time ranges C and D is 20 ms, Figures 6B and 7B show the case where the interval between time ranges C and D is 24 ms, and Figures 6C and 7C show the case where the interval between time ranges C and D is 30 ms. The interval between time ranges A and B is 50 ms.

As shown in Figure 7A, when the interval between time ranges C and D becomes short, the first index value x and the second index value y diverge even in the case of a pseudo waveform that should not be detected as an R wave. On the other hand, as shown in Figure 6C, when the interval between time ranges C and D becomes long, the first index value x and the second index value y approach each other even in the case of an ECG waveform. In order to distinguish between an ECG waveform and a pseudo waveform, it is preferable to set the interval between time ranges C and D in the range of 20 ms to 30 ms.

[Example]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 8 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 sequence of an ECG waveform, a storage unit 2 that stores the sampling data sequence of the ECG waveform and information on the sampling time, a positive/negative inversion value calculation unit 3 that calculates a positive/negative inversion value of the time difference of the sampling data from the sampling data sequence of the ECG waveform for each sampling time, a maximum value detection unit 4 that detects a maximum value M1 of the positive/negative inversion value of the time difference in a time range A before the sampling time to be processed and the positive/negative inversion value of the time difference in a time range B after the sampling time to be processed for each sampling time, an index value calculation unit 5 that calculates a first index value x for each sampling time by subtracting the maximum value M1 from the positive/negative inversion value of the time difference at the sampling time to be processed, and an index value storage unit 6 that receives the first index value x as an input.

The heartbeat detection device further includes a maximum value detection unit 7 that detects, for each sampling time, a maximum value M2 of the inverted positive and negative time difference value in a time range C before the sampling time to be processed and the inverted positive and negative time difference value in a time range D after the sampling time to be processed; an index value calculation unit 8 that calculates, for each sampling time, a second index value y obtained by subtracting the maximum value M2 from the inverted positive and negative time difference value at the sampling time to be processed; an index value storage unit 9 that receives as input the second index value y; and a heartbeat time determination unit 10 that determines the first sampling time as the heartbeat time when the second index value y at the first sampling time when the first index value x exceeds a threshold value TH and the first index value x at a second sampling time that has a predetermined relationship with the first sampling time satisfy a predetermined condition.

FIG. 9 is a block diagram showing an example of the configuration of maximum value detection units 4 and 7, index value calculation units 5 and 8, and index value storage units 6 and 9.
The maximum value detection unit 4 is composed of a FIFO buffer (First In, First Out) 40 which receives as input the time difference positive/negative inversion value calculated by the positive/negative inversion value calculation unit 3, a FIFO buffer 41 which receives as input the output value of the FIFO buffer 40, a FIFO buffer 42 which receives as input the output value of the FIFO buffer 41, and a detection processing unit 43 which detects the maximum value M1 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 for each sampling time.

The index value calculation unit 5 is composed of a FIFO buffer 50 which receives as input the time difference positive/negative inverted value calculated by the positive/negative inverted value calculation unit 3, and a subtraction processing unit 51 which calculates a first index value x for each sampling time by subtracting the maximum value M1 detected by the maximum value detection unit 4 from the output value of the FIFO buffer 50.
The index value storage unit 6 is composed of a FIFO buffer 60 to which the first index value x calculated by the subtraction processing unit 51 is input.

The maximum value detection unit 7 is composed of a FIFO buffer 70 which receives as input the time difference positive/negative inversion value calculated by the positive/negative inversion value calculation unit 3, a FIFO buffer 71 which receives as input the output value of the FIFO buffer 70, a FIFO buffer 72 which receives as input the output value of the FIFO buffer 71, and a detection processing unit 73 which detects the maximum value M2 of the time difference positive/negative inversion value stored in the FIFO buffer 70 and the time difference positive/negative inversion value stored in the FIFO buffer 72 at each sampling time.

The index value calculation unit 8 is composed of a FIFO buffer 80 which receives as input the time difference positive/negative inversion value calculated by the positive/negative inversion value calculation unit 3, and a subtraction processing unit 81 which calculates a second index value y for each sampling time by subtracting the maximum value M2 detected by the maximum value detection unit 7 from the output value of the FIFO buffer 80.
The index value storage unit 9 is composed of a FIFO buffer 90 to which the second index value y calculated by the subtraction processing unit 81 is input.

The heartbeat detection method of this embodiment will be described below with reference to Figures 10 to 12. Here, the procedure for detecting one heartbeat and obtaining the heartbeat time will be described. By repeating this calculation of the heartbeat time over the period of the ECG waveform data, time series data of the heartbeat time can be obtained.

In this embodiment, the data sequence 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 string D(i) of the ECG waveform. At this time, the electrocardiograph 1 adds information on the sampling time to each sampling data and outputs it. Note that a specific method for measuring the ECG waveform is a well-known technique, so a detailed description will be omitted.
The storage unit 2 stores the sampling data string D(i) of the ECG waveform output from the electrocardiograph 1 and 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 acquires the data D(i+1) after one sampling of the sampling data D(i) and the data D(i-1) before one sampling from the storage unit 2 (step S1 in FIG. 10). Then, the positive/negative inversion value calculation unit 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. 10).
Y(i)=-{D(i+1)-D(i-1)} ...(1)

The maximum value detector 4 and the index value calculator 5 calculate the first index value x (step S3 in FIG. 10). Specifically, the positive/negative inversion value calculator 3 inputs the calculated time difference positive/negative inversion value Y(i) to the FIFO buffer 50 at each sampling time (step S100 in FIG. 11). The input value is held in the FIFO buffer 50 and is used for subtraction processing after a time equivalent to the size of the FIFO buffer 50 (the delay time from when the time difference positive/negative inversion value is input to the FIFO buffer 50 until it is output).

The positive/negative inversion value calculation unit 3 also inputs the calculated time difference positive/negative inversion value Y(i) to the FIFO buffer 40 for each sampling time (step S101 in FIG. 11). The output of the FIFO buffer 40 is input to the FIFO buffer 41 (step S102 in FIG. 11), and the output of the FIFO buffer 41 is input to the FIFO buffer 42 (step S103 in FIG. 11). The FIFO buffers 40 to 42 are used to find the maximum value of the time difference positive/negative inversion value in the time ranges A and B.

The time interval L3 (the delay time from when the time difference positive/negative inversion value is input to the FIFO buffer 41 until it is output) corresponding to the length of the FIFO buffer 41 must be sufficiently wide relative 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 (the delay time from when the time difference positive/negative inversion value is input to the FIFO buffer 40 until it is output) corresponding to the length of the FIFO buffer 40 and the time interval 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) corresponding to the length of the FIFO buffer 42 are appropriately about 100 ms.

The time interval L1, which corresponds to the length of the FIFO buffer 50, 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 M1 for the ranges of -(L2 + L3/2) to -(L3/2) and (L3/2) to (L2 + L3/2) for the time of the output value b of the FIFO buffer 50 (the sampling time to be processed), and it is possible to subtract the maximum value M1 from the output value b.

The detection processing unit 43 detects a maximum value M1 of the positive/negative inverted time difference values stored in the FIFO buffer 40 and the positive/negative inverted time difference values stored in the FIFO buffer 42 for each sampling time (step S104 in FIG. 11).
The subtraction processing unit 51 calculates a first index value x(i)=b-M1 by subtracting the maximum value M1 from the output value b of the FIFO buffer 50 for each sampling time (step S105 in FIG. 11).

In this way, the maximum value detection unit 4 and the index value calculation unit 5 perform the processing of step S3, and at the same time, the maximum value detection unit 7 and the index value calculation unit 8 calculate the second index value y (step S4 in Figure 10).

Specifically, the positive/negative inversion value calculation unit 3 inputs the calculated time difference positive/negative inversion value Y(i) to the FIFO buffer 80 for each sampling time (step S200 in FIG. 12). The positive/negative inversion value calculation unit 3 also inputs the calculated time difference positive/negative inversion value Y(i) to the FIFO buffer 70 for each sampling time (step S201 in FIG. 12). The output of the FIFO buffer 70 is input to the FIFO buffer 71 (step S202 in FIG. 12), and the output of the FIFO buffer 71 is input to the FIFO buffer 72 (step S203 in FIG. 12). The FIFO buffers 70 to 72 are used to find the maximum value of the time difference positive/negative inversion value in the time ranges C and D.

In the above example, the time interval L7 (the delay time from when the time difference positive/negative inverted value is input to the FIFO buffer 71 until it is output) corresponding to the length of the FIFO buffer 71 is, for example, 24 ms. This interval L7 is the interval between time ranges C and D. In addition, the time interval L6 (the delay time from when the time difference positive/negative inverted value is input to the FIFO buffer 70 until it is output) corresponding to the length of the FIFO buffer 70 and the time interval L8 (the delay time from when the time difference positive/negative inverted value is input to the FIFO buffer 72 until it is output, L6 = L8) corresponding to the length of the FIFO buffer 72 are appropriately about 113 ms. As is clear from the above explanation, L2 + L3 + L4 = L6 + L7 + L8.

The time interval L5, which corresponds to the length of the FIFO buffer 80, can be set as L5 = L6 + L7/2. Therefore, in the above numerical example, L5 is 125 ms. This value is the same as the length L1 of the FIFO buffer 50. By setting L5 = L6 + L7/2 and L6 = L8, it is possible to find the maximum value M2 in the ranges of -(L6 + L7/2) to -(L7/2) and (L7/2) to (L6 + L7/2) for the time of the output value c of the FIFO buffer 80 (the sampling time to be processed), and it is possible to subtract the maximum value M2 from the output value c.

The detection processing unit 73 detects a maximum value M2 of the positive/negative inverted time difference values stored in the FIFO buffer 70 and the positive/negative inverted time difference values stored in the FIFO buffer 72 for each sampling time (step S204 in FIG. 12).
The subtraction processing unit 81 calculates a second index value y(i)=c-M2 for each sampling time by subtracting the maximum value M2 from the output value c of the FIFO buffer 80 (step S205 in FIG. 12). In this manner, the process of step S4 is performed by the maximum value detection unit 7 and the index value calculation unit 8.

The subtraction processing unit 51 inputs the calculated first index value x(i) to the FIFO buffer 60 for each sampling time (step S5 in FIG. 10). At the same time, the subtraction processing unit 81 inputs the calculated second index value y(i) to the FIFO buffer 90 for each sampling time (step S6 in FIG. 10).

The heartbeat time determination unit 10 acquires the first index value x(i) = x3 and the second index value y(i) = y3 stored in the first position of the FIFO buffer 60, 90. The heartbeat time determination unit 10 also acquires the first index value x(i-1) = x2, which is stored in the second position of the FIFO buffer 60 and is one sampling (1 ms) earlier than the first index value x(i) = x3. The heartbeat time determination unit 10 also acquires the first index value x(i-2) = x1, which is stored in the third position of the FIFO buffer 60 and is two samplings (2 ms) earlier than the first index value x(i) = x3.

When the first index value x(i) = x3 exceeds the threshold value TH (YES in step S7 of Figure 10) and the first index value x(i) = x3 has increased relative to the first index value x(i-1) = x2 of the previous sampling (YES in step S8 of Figure 10), if the second index value y(i) = y3 at the same time as the first index value x(i) = x3 and the first index value x(i-2) = x1 of the previous sampling satisfy the condition (x1-y3) > a (YES in step S9 of Figure 10), the heartbeat time determination unit 10 determines the sampling time of the first index value x(i) = x3 to be the heartbeat time (step S10 of Figure 10).

As described above, the time difference positive/negative inverted value Y(i) is calculated from the sampling data D(i), and the first index value x(i) is calculated from the time difference positive/negative inverted value Y(i). Therefore, the sampling time of the first index value x(i) is the sampling time of the time difference positive/negative inverted value Y(i) (the sampling time of the data D(i)), and can be obtained from the storage unit 2.
In this way, the processes of steps S1 to S10 are repeatedly executed for each sampling period, thereby obtaining time series data of heartbeat times.

In this embodiment, it is determined whether the second index value y(i) = y3 at the first sampling time (t3 in the example of Figure 3) at which the first index value x(i) = x3 exceeds the threshold value TH, and the first index value x(i-2) = x1 at the second sampling time (t1 in the example of Figure 3) which has a predetermined relationship with the first sampling time, satisfy a condition; however, the second sampling time only needs to be a time a predetermined time in the past with respect to the first sampling time, and does not have to be two samples (2 ms) earlier.

The memory unit 2, positive/negative inversion value calculation unit 3, maximum value detection units 4 and 7, index value calculation units 5 and 8, index value memory units 6 and 9, and heartbeat time determination unit 10 of the heartbeat 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 13.

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...positive/negative inversion value calculation unit, 4, 7...maximum value detection unit, 5, 8...index value calculation unit, 6, 9...index value memory unit, 10...heartbeat time determination unit, 40-42, 50, 60, 70-72, 80, 90...FIFO buffer, 43, 73...detection processing unit, 51, 81...subtraction processing unit.

Claims (8)

A first step of calculating a positive/negative inversion value of a time difference of sampled data from a sampled data string of an electrocardiogram waveform of a living body for each sampling time;
a second step of detecting, for each sampling time, a first maximum value among the positive/negative inverted value in a first time range before the sampling time to be processed and the positive/negative inverted value in a second time range after the sampling time to be processed;
a third step of detecting, for each sampling time, a second maximum value among the positive/negative inverted value in a third time range before the sampling time to be processed and the positive/negative inverted value in a fourth time range after the sampling time to be processed;
a fourth step of calculating, for each sampling time, a subtraction value obtained by subtracting the first maximum value from the positive/negative inverted value at the sampling time to be processed as a first index value;
a fifth step of calculating, for each sampling time, a subtraction value obtained by subtracting the second maximum value from the positive/negative inverted value at the sampling time to be processed as a second index value;
and a sixth step of setting the first sampling time as the heartbeat time when the second index value at a first sampling time at which the first index value exceeds a predetermined threshold and the first index value at a second sampling time having a predetermined relationship with the first sampling time satisfy a predetermined condition. 2. The method for detecting a heartbeat according to claim 1,
a timing of a leading edge of the third time range with respect to the sampling time of the processing target is the same as a timing of a leading edge of the first time range;
a timing of a trailing edge of the fourth time range with respect to the sampling time of the processing target is the same as a timing of a trailing edge of the second time range;
A heartbeat detection method, comprising: a time interval between the third time range and the fourth time range being shorter than a time interval between the first time range and the second time range. 3. The heartbeat detection method according to claim 1, further comprising:
The heartbeat detection method, characterized in that the sixth step includes a step of setting the first sampling time as the heartbeat time when the first index value at the first sampling time increases relative to the first index value prior to the first sampling time, and the second index value at the first sampling time and the first index value at the second sampling time satisfy a predetermined condition. The method for detecting a heartbeat according to any one of claims 1 to 3,
A heartbeat detection method, characterized in that the interval between the third time range and the fourth time range is in the range of 20 ms to 30 ms. a positive/negative inversion value calculation unit configured to calculate a positive/negative inversion value of a time difference of sampled data from a sampled data string of an electrocardiogram waveform of a living body for each sampling time;
a first maximum value detection unit configured to detect, for each sampling time, a first maximum value among the positive/negative inverted value in a first time range before a sampling time to be processed and the positive/negative inverted value in a second time range after the sampling time to be processed;
a second maximum value detection unit configured to detect, for each sampling time, a second maximum value among the positive/negative inverted value in a third time range prior to the sampling time of the processing target and the positive/negative inverted value in a fourth time range after the sampling time of the processing target;
a first index value calculation unit configured to calculate, for each sampling time, a subtraction value obtained by subtracting the first maximum value from the positive/negative inverted value at the sampling time to be processed as a first index value;
a second index value calculation unit configured to calculate, for each sampling time, a subtraction value obtained by subtracting the second maximum value from the positive/negative inverted value at the sampling time of the processing target, as a second index value;
a heartbeat time determination unit configured to determine the first sampling time as the heartbeat time when the second index value at a first sampling time at which the first index value exceeds a predetermined threshold and the first index value at a second sampling time that has a predetermined relationship with the first sampling time satisfy a predetermined condition. 6. The heartbeat detection device according to claim 5,
a timing of a leading edge of the third time range with respect to the sampling time of the processing target is the same as a timing of a leading edge of the first time range;
a timing of a trailing edge of the fourth time range with respect to the sampling time of the processing target is the same as a timing of a trailing edge of the second time range;
A heartbeat detection device, wherein an interval between the third time range and the fourth time range is shorter than an interval between the first time range and the second time range. 7. The heart rate detection device according to claim 5,
The heartbeat time determination unit determines the first sampling time as the heartbeat time when the first index value at the first sampling time increases relative to the first index value prior to the first sampling time, and the second index value at the first sampling time and the first index value at the second sampling time satisfy a predetermined condition. The heart rate detection device according to any one of claims 5 to 7,
A heart rate detection device, wherein the interval between the third time range and the fourth time range is in the range of 20 ms to 30 ms.

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