Heart rate detection system, heart rate detection method, and information storage medium

Abstract

Provided is a heart rate detection system capable of detecting the heart rate of a subject being measured at high precision.　This heart rate detection system includes: a Doppler data acquisition unit (31) that acquires measurement data including a waveform component caused by movement of the heart of a subject being measured; a band filter unit (32) that applies a band filter of a given passband to the measurement data; a heart rate estimation unit (33) that estimates the heart rate of the subject being measured on the basis of the measurement data to which the band filter (32) has been applied; and a band change unit (34) that changes the band of the band filter (32) on the basis of the estimated heart rate.

Description

Heart rate detection system, heart rate detection method, and information storage medium

[0001] The present invention relates to a heart rate detection system, a heart rate detection method, and an information storage medium, and more particularly to a technique for detecting the heart rate of a person being measured from measurement data that includes waveform components caused by cardiac movement.

[0002] Various systems for detecting the heart rate of a person being measured have been studied. One known example is a method for detecting the heart rate without contact using a microwave Doppler sensor, as described in Patent Document 1 below. The microwave Doppler sensor can convert the movement of the person's chest into data, from which the heart rate can be detected.

[0003] JP 2017-134795 A

[0004] Generally, measurement data obtained from a subject contains many noise components in addition to components due to cardiac motion, so it is conceivable to apply a bandpass filter to the measurement data and detect the subject's heart rate based on the measurement data from which the noise has been removed. However, because the cardiac motion f of the subject changes in a complex manner depending on the heart rate, using a filter with a fixed passband may actually reduce the accuracy of heart rate detection.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a heart rate detection system, a heart rate detection method, and an information storage medium that can accurately detect the heart rate of a person being measured from measurement data that includes waveform components caused by cardiac movement.

[0006] (1) In order to solve the above problem, the heart rate detection system of the present invention includes a measurement data acquisition means for acquiring measurement data including waveform components resulting from the movement of the subject's heart, a band pass filter means for applying a band pass filter of a given pass band to the measurement data, a heart rate estimation means for estimating the heart rate of the subject based on the measurement data to which the band pass filter has been applied, and a band change means for changing the band of the band pass filter based on the estimated heart rate.

[0007] (2) The heart rate detection system according to (1) may further include a band storage unit that stores the heart rate value and an upper limit value and a lower limit value of the band in association with each other. The band changing unit may determine the band of the band filter after the change based on the contents stored in the band storage unit.

[0008] (3) In the heart rate detection system described in (2), the band storage means may store the common upper limit value in association with the heart rate that is equal to or less than a predetermined value.

[0009] (4) In the heart rate detection system according to (2) or (3), the band storage means may store the common lower limit value in association with the heart rate equal to or greater than the predetermined value.

[0010] (5) In the heart rate detection system according to any one of (2) to (4), the band storage means may associate a smaller lower limit value with a heart rate value that is less than the predetermined value, and may associate a larger upper limit value with a heart rate value that is higher than the predetermined value.

[0011] (6) In the heart rate detection system described in any one of (1) to (5), the band changing means may change the band of the band filter in accordance with the amount of change in the value of the heart rate estimated based on the measurement data to which the band filter of the same band has been applied.

[0012] (7) In the heart rate detection system according to any one of (1) to (6), the measurement data may be Doppler data acquired by a Doppler sensor.

[0013] (8) A heart rate detection method according to the present invention includes a measurement data acquisition step of acquiring measurement data including waveform components resulting from cardiac movement of a subject; a band pass filter step of applying a band pass filter of a given pass band to the measurement data; a heart rate estimation step of estimating the heart rate of the subject based on the measurement data to which the band pass filter has been applied; and a band change step of changing the band of the band pass filter based on the estimated heart rate.

[0014] (9) A program according to the present invention causes a computer to function as measurement data acquiring means for acquiring measurement data including waveform components resulting from cardiac movement of a subject, bandpass filtering means for applying a bandpass filter of a given passband to the measurement data, heart rate estimating means for estimating the heart rate of the subject based on the measurement data to which the bandpass filter has been applied, and band changing means for changing the band of the bandpass filter based on the estimated heart rate. This program may be stored in a computer-readable information storage medium such as a semiconductor memory or a magneto-optical disk.

[0015] FIG. 1 is a configuration diagram of a heart rate detection system according to an embodiment of the present invention; FIG. 2 is a functional block diagram of a data processing device; FIG. 3 is a diagram schematically showing the contents stored in a band storage unit; FIG. 4 is a diagram showing an electrocardiogram waveform; FIG. 5 is a diagram showing frequency bands corresponding to each part of the electrocardiogram waveform; FIG. 6 is a diagram explaining a procedure for determining the upper and lower limits of the pass band of a band filter; and FIG. 7 is a flow chart showing the operation of the heart rate detection system according to the present embodiment.

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0017] 1 is a configuration diagram of a heart rate detection system according to an embodiment of the present invention. As shown in the figure, the heart rate detection system 1 includes a Doppler sensor 2 and a data processing device 3. The heart rate detection system 1 is installed, for example, in a home and detects the heart rate of a person being measured while sleeping. The Doppler sensor 2 is installed, for example, near a bed and directed toward the chest of the person being measured.

[0018] Microwaves are emitted from the Doppler sensor 2, and the reflected waves from the vicinity of the subject's heart are received by the Doppler sensor 2. The reflected waves are frequency shifted due to the Doppler effect, and by observing this, the subject's heart rate can be obtained. The reflected waves are detected by quadrature detection as a Doppler signal containing an I signal and its quadrature component, a Q signal, and converted into digital Doppler data before being output to the data processing device 3. The Doppler data input to the signal processing device 3 is time-series data, indicating the amplitude (I component and Q component) at each time.

[0019] The data processing device 3 may be configured as a known computer, for example, including a CPU, memory, input device, and display, and by executing the data processing program according to this embodiment, generates the heart rate of the subject based on the Doppler data output from the Doppler sensor 2.

[0020] 2 is a functional block diagram of the data processing device 3. As shown in the figure, the data processing device 3 functionally includes a Doppler data acquisition unit 31, a band filter 32, a heart rate estimation unit 33, a band change unit 34, and a band storage unit 35. The heart rate estimation unit 33 includes an FFT unit 33a and a peak identification unit 33b. These functions are realized by the data processing device 3, which is a computer, executing the data processing program. The data processing program may be read by the data processing device 3 from a computer-readable information storage medium such as a semiconductor memory or a magneto-optical disk. Alternatively, the data processing program may be downloaded to the data processing device 3 from a communication network such as the Internet.

[0021] The Doppler data acquisition unit 31 acquires Doppler data indicating the movement of the subject's chest, which is acquired by the Doppler sensor 2. The Doppler data includes components attributable to the movement of the subject's heart as well as other components attributable to the subject's body movement and breathing, and is an example of "measurement data" in the present invention.

[0022] The bandpass filter 32 applies a bandpass filter to the Doppler data acquired by the Doppler data acquisition unit 31. This extracts components resulting from the heart movement of the subject from the Doppler data. Default upper and lower limit frequencies are stored in advance in memory as the passband of the bandpass filter. Furthermore, when the band change unit 34 writes the upper and lower limit frequencies to memory, the bandpass filter is applied using the written values.

[0023] The heart rate estimation unit 33 estimates the heart rate of the subject based on the Doppler data to which the bandpass filter has been applied. In one configuration example, the FFT unit 33a may perform an FFT (fast Fourier transform) on the Doppler data to obtain a frequency spectrum of the Doppler data. The peak identification unit 33b may then identify a peak in the frequency spectrum resulting from the FFT, and use that value as the subject's heart rate.

[0024] The band changing unit 34 changes the band of the band filter based on the heart rate estimated by the heart rate estimation unit 33. Specifically, it writes the upper and lower limit values ​​of the pass band determined based on the heart rate to memory. These values ​​are read by the band filter 32 and used as pass band information. The band changing unit 34 stores the default heart rate (e.g., 60 BPM) of the data processing device 3 in memory. When changing the band of the band filter, it stores the estimated value of the heart rate used to determine the band in memory instead of the default heart rate. The band changing unit 34 changes the band again if the current estimated value of the heart rate has changed by more than a threshold value from the value stored in memory.

[0025] The band change unit 34 may determine the band of the band filter after the change based on the contents stored in the band storage unit 35. FIG. 3 is a diagram schematically illustrating the contents stored in the band storage unit 35. As shown in the figure, the band storage unit 35 stores, for example, heart rate values ​​from 20 to 140 (BPM) in 10-degree increments, in association with the upper and lower limits (Hz) of the pass band of the band filter for each heart rate value. Here, the band storage unit 35 stores a common upper limit of 16.7 (Hz) associated with heart rates from 20 to 60 (BPM) that are equal to or less than the reference heart rate of 60 (BPM). The band storage unit 35 also stores a common lower limit of 4.0 Hz associated with heart rates equal to or greater than 60 (BPM). Furthermore, for heart rates less than 60 (BPM), the band storage unit 35 associates a lower lower limit with the smaller heart rate value. Furthermore, for heart rates higher than 60 BPM, the higher the heart rate value, the higher the associated upper limit value. Based on the contents stored in the band memory unit 35 shown in the figure, the upper and lower limit values ​​of the pass band corresponding to the heart rate estimated by the heart rate estimation unit 33 are read out, and these values ​​are used by the band filter 32. Note that the heart rate values ​​shown in the figure are in increments of 10, but if a value between these is estimated by the heart rate estimation unit 33, the upper and lower limit values ​​of the pass band can be determined by interpolating the upper and lower limit values ​​corresponding to the preceding and following heart rate values, respectively.

[0026] Here, the passband of the bandpass filter is set taking into account the electrocardiogram waveform of a healthy subject. Figure 4 shows an electrocardiogram waveform. The vertical axis represents the detected potential of the electrocardiograph, and the horizontal axis represents time. As shown in the figure, the electrocardiogram waveform of a healthy subject includes, in chronological order, P waves, QRS waves, T waves, and U waves. Specifically, QRS waves include Q waves, R waves, and S waves. As shown in Figure 5, the normal time width of P waves is 60 to 100 ms. This corresponds to a frequency range of 10 to 16.7 Hz. Similarly, the normal time width of QRS waves is 60 to 100 ms, which corresponds to a frequency range of 10 to 16.7 Hz. The normal time width of T waves is 100 to 250 ms, which corresponds to a frequency range of 4 to 10 Hz. The normal time width of U waves is 160 to 250 ms, which corresponds to a frequency range of 4 to 6.25 Hz. These values ​​are those when the subject's heart rate is a reference heart rate of 60 (BPM).

[0027] Here, FIG. 6 is a diagram illustrating a procedure for determining the upper and lower limits of the passband width of a band-pass filter. It is generally known that QRS waves and T waves are affected by the heart rate. Specifically, in the clinical field, a corrected QT interval is calculated by dividing the QT interval, which is the time from the start of the Q wave to the end of the T wave, by the square root of the R-R interval (the time from the peak of the R wave to the peak of the next R wave), which is the reciprocal of the heart rate. Then, by comparing this corrected QT interval with a standard QT interval, abnormalities in the electrocardiogram waveform are determined.

[0028] Taking this into consideration, the normal values ​​of the time widths of the QRS wave and T wave shown in FIG. 4 can be corrected as follows. That is, as shown in FIG. 4, when the reference heart rate is 60 beats per minute (BPM), the normal value of the time width of the QRS wave is 60 to 100 milliseconds. Therefore, when the R-R time, which is the reciprocal of the heart rate, is α (s), the normal value of the time width of the QRS wave is 60 × √α to 100√α (ms). This range of normal values ​​of the time width can be converted into a frequency range. For example, FIG. 6 shows that when the heart rate is 20, the R-R time is 3.00 (the reciprocal of the heart rate), and the normal value of the time width of the QRS wave is 104 (= 60 × √3) to 173 (= 100√3) (ms). It also shows that the corresponding frequency range is 5.8 to 9.6 Hz.

[0029] Similarly, when the reference heart rate is 60 beats per minute (BPM), the normal value of the T-wave duration is 100 to 250 ms. Therefore, when the R-R time, which is the reciprocal of the heart rate, is α (s), the normal value of the T-wave duration is 100 × √α to 250√α (ms). This range of normal values ​​of duration can also be converted into a frequency range. For example, FIG. 6 shows that when the heart rate is 20, the R-R time is 3.00 (the reciprocal of the heart rate), and the normal value of the T-wave duration is 173 (= 100 × √3) to 433 (= 250√3) (ms). It also shows that the corresponding frequency range is 2.3 to 5.8 Hz.

[0030] Also shown in Figure 6 are the frequency ranges of the P and U waves transcribed from Figure 5. Since the P and U waves are not affected by the heart rate, common values ​​are set for all heart rates.

[0031] In this embodiment, the passband of the band-pass filter is set so as to reliably pass all of the partial wave components, such as P waves, QRS waves, T waves, and U waves, that make up the electrocardiogram waveform. Therefore, the maximum value of the upper and lower limit frequencies of each partial wave is set as the upper limit of the passband, and the minimum value is set as the lower limit. For example, in FIG. 6 , for a heart rate of 20 BPM, the maximum value is 16.7 Hz, which is the upper limit frequency of the P waves, and the minimum value is 2.3 Hz, which is the lower limit frequency of the T waves. These values ​​are stored in the band storage unit 35 as shown in FIG. 3 . The same applies to heart rates of 30 to 50 BPM.

[0032] Furthermore, when the heart rate is 140 BPM, the maximum value is 25.5 Hz, which is the upper limit frequency of the QRS wave, and the minimum value is 4.0 Hz, which is the lower limit frequency of the U wave. These values ​​are stored in the band storage unit 35 as shown in Fig. 3. The same applies to heart rates of 70 to 130 BPM.

[0033] In the case of the reference heart rate (60), the maximum value is 16.7 (Hz), which is the upper limit frequency of the QRS wave and the upper limit frequency of the P wave, and the minimum value is 4.0, which is the lower limit frequency of the T wave and the lower limit frequency of the U wave. These values ​​are stored in the band memory unit 35 as shown in FIG.

[0034] In this embodiment, the values ​​stored in the band memory unit 35 are determined based on the electrocardiogram waveform as described above. Therefore, when the heart rate is high (60 to 140), the lower limit of the frequency is the upper limit of the U wave, and is constant regardless of the heart rate. On the other hand, the upper limit of the frequency is the upper limit of the QRS wave, and its value increases with the heart rate. When the heart rate is low (20 to 60), the upper limit of the frequency is the upper limit of the P wave. Furthermore, the lower limit of the frequency is the lower limit of the T wave, and its value increases with the heart rate. This allows the passband of the band filter to be appropriately set for each heart rate. In other words, it is possible to cut out only unnecessary frequency components and reliably pass necessary frequency components, thereby improving the accuracy of heart rate estimation.

[0035] 7 is a flow diagram showing the operation of the heart rate detection system 1 according to this embodiment. As shown in the figure, in the heart rate detection system 1, the Doppler data acquisition unit 31 first acquires Doppler data output from the Doppler sensor 2 (S701). Next, the band-pass filter 32 reads the upper and lower limit values ​​of the pass band stored in memory (S702). At this time, if there are no upper and lower limit values ​​written by the band change unit 34 (S703), the band-pass filter 32 reads default upper and lower limit values ​​separately stored in memory (S704). Then, the heart rate estimation unit 33 estimates the heart rate of the subject using the read upper and lower limit values ​​(S705). At this time, if the estimated heart rate value is different from the heart rate value stored in memory by the band change unit 34 by more than a predetermined threshold (S706), the band change unit 34 calculates the upper and lower limits of the pass band based on the latest heart rate value estimated by the heart rate estimation unit 33, stores these values ​​in memory, and also stores the latest estimated heart rate value in memory (S707), and returns to processing of S701.

[0036] According to the heart rate detection system 1 described above, the passband of the band filter 32 is changed in accordance with the estimated heart rate, thereby optimizing the processing of the band filter 32 and improving the accuracy of estimating the heart rate. In particular, the band set in the band filter 32 is determined based on the electrocardiogram waveform, allowing the band filter 32 to appropriately pass waveform components related to the movement of the subject's heart. Furthermore, the band change unit 34 stores the estimated heart rate at the time of band change in memory, and determines the timing of the next band change based on this estimated value, thereby preventing excessive repetition of band changes.

[0037] The present invention is not limited to the above-described embodiments and various modifications are possible, and such modifications are also within the scope of the present invention. For example, in the above description, Doppler data was used as measurement data containing waveform components attributable to the subject's cardiac movement. However, the present invention can also be applied to data obtained by other measurement methods. For example, a microdisplacement sensor including a piezoelectric element may be brought into contact with the subject to obtain measurement data indicating the subject's minute movements. Alternatively, measurement data indicating the subject's blood flow may be obtained contactlessly or non-contactly using a photoplethysmography method or the like. Such measurement data also contains components attributable to the subject's cardiac movement, and the subject's heart rate can be detected by applying the present invention.

Claims

1. A heart rate detection system comprising: a measurement data acquisition means for acquiring measurement data including waveform components attributable to cardiac movement of a subject; a band pass filter means for applying a band pass filter of a given pass band to the measurement data; a heart rate estimation means for estimating the heart rate of the subject based on the measurement data to which the band pass filter has been applied; and a band changing means for changing the band of the band pass filter based on the estimated heart rate.

2. A heart rate detection system as described in claim 1, further comprising band storage means for storing the value of the heart rate in association with the upper and lower limits of the band, and the band changing means for determining the band of the changed band filter based on the contents stored in the band storage means.

3. A heart rate detection system according to claim 2, wherein the band storage means stores a common upper limit value in association with the heart rate that is equal to or lower than a predetermined value.

4. A heart rate detection system according to claim 3, wherein said band storage means stores a common lower limit value in association with said heart rate equal to or greater than said predetermined value.

5. A heart rate detection system as described in claim 4, characterized in that the band memory means associates, for a heart rate below the predetermined value, a lower limit value that is smaller as the heart rate value decreases, and, for a heart rate higher than the predetermined value, associates, for a heart rate higher than the predetermined value, a higher upper limit value that is larger as the heart rate value increases.

6. A heart rate detection system as described in claim 1, characterized in that the band changing means changes the band of the band filter in accordance with the amount of change in the value of the heart rate estimated based on the measurement data to which the band filter of the same band has been applied.

7. A heart rate detection system according to claim 1, characterized in that the measurement data is Doppler data acquired by a Doppler sensor.

8. A heart rate detection method comprising: a measurement data acquisition step of acquiring measurement data including waveform components attributable to cardiac movement of a subject; a band pass filter step of applying a band pass filter of a given pass band to the measurement data; a heart rate estimation step of estimating the heart rate of the subject based on the measurement data to which the band pass filter has been applied; and a band changing step of changing the band of the band pass filter based on the estimated heart rate.

9. A computer-readable information storage medium storing a program for causing a computer to function as: measurement data acquisition means for acquiring measurement data including waveform components attributable to cardiac movement of a subject; bandpass filter means for applying a bandpass filter of a given passband to the measurement data; heart rate estimation means for estimating the heart rate of the subject based on the measurement data to which the bandpass filter has been applied; and band changing means for changing the band of the bandpass filter based on the estimated heart rate.

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