JP7472741B2 - Pulse rate measuring device and program - Google Patents

Description

The present invention relates to a pulse rate measuring device and program for measuring a person's pulse rate.

Conventionally, there is known a technique for acquiring an electrocardiogram signal using multiple pulse wave sensors. Patent Document 1 discloses using a pulse wave sensor that outputs an electrocardiogram signal with the largest R-wave amplitude among multiple pulse wave sensors.

JP 2020-28478 A

In conventional technology, one pulse wave sensor is selected from multiple pulse wave sensors based on the amplitude of the R wave of the measured electrocardiogram signal, but because the R wave is pulse-shaped, it is easily attenuated. As a result, it is easily affected by the state in which the pulse wave sensor is attached, and it is not optimal to measure the pulse rate based on the electrocardiogram signal with the largest amplitude of the R wave, which creates a problem in that the accuracy of the pulse rate measurement may decrease.

Therefore, the present invention was made in consideration of these points, and aims to improve the accuracy of measuring pulse rate.

The pulse rate measuring device of the first aspect of the present invention has a signal acquisition unit that acquires multiple pulse wave signals from multiple pulse wave sensors attached to multiple positions on the body of a person whose pulse rate is to be measured, a signal conversion unit that converts the multiple pulse wave signals into multiple frequency domain data by Fourier transforming each of the multiple pulse wave signals, a selection unit that selects, from the multiple frequency domain data, frequency domain data whose level in a predetermined frequency range or whose signal-to-noise ratio is equal to or greater than an allowable value, and a pulse rate identification unit that identifies the pulse rate based on the frequency domain data selected by the selection unit.

The device may further include a calculation unit that calculates a provisional pulse period based on the time between adjacent peaks of at least any of the plurality of pulse wave signals, and the signal conversion unit may determine the period of the plurality of pulse wave signals to be subjected to Fourier transform based on the pulse period.

The signal conversion unit may be configured to extend the period of the multiple pulse wave signals to be subjected to Fourier transformation as the pulse period becomes longer.

The signal conversion unit may generate the plurality of frequency domain data by Fourier transforming the plurality of pulse wave signals over a first period, and when the quality of at least one of the plurality of frequency domain data satisfies a predetermined condition, may determine that the period for which the plurality of pulse wave signals are to be Fourier transformed is a second period that is shorter than the first period.

The signal conversion unit may determine that the period to be subjected to the Fourier transform is the second period when the quality of the frequency domain data selected by the selection unit from among the multiple frequency domain data generated by Fourier transforming the multiple pulse wave signals over the first period satisfies the predetermined condition.

The selection unit may select frequency domain data in which the level or signal-to-noise ratio of the specified frequency range, which includes pulse wave components in the plurality of frequency domain data and harmonic components of the pulse wave components within a specified order, is equal to or greater than an allowable value.

The program of the second aspect of the present invention causes a computer to function as a signal acquisition unit that acquires multiple pulse wave signals from multiple pulse wave sensors attached to multiple positions on the body of a person whose pulse rate is to be measured, a signal conversion unit that converts the multiple pulse wave signals into multiple frequency domain data by Fourier transforming each of the multiple pulse wave signals, a selection unit that selects, from the multiple frequency domain data, frequency domain data whose level in a predetermined frequency range or whose signal-to-noise ratio is equal to or greater than an allowable value, and a pulse rate determination unit that determines the pulse rate based on the frequency domain data selected by the selection unit.

The present invention has the effect of improving the accuracy of measuring pulse rate.

FIG. 1 is a diagram showing an overview of a pulse rate measuring system. 3 is a diagram illustrating pulse wave signals output from a plurality of pulse wave sensors. FIG. FIG. 1 is a diagram showing a configuration of a pulse rate measuring device. FIG. 11 is a diagram for explaining the operation of a calculation unit. 11 is a diagram illustrating an example of frequency domain data generated by a signal conversion unit. FIG. FIG. 4 is a diagram showing a plurality of frequency domain data corresponding to a plurality of pulse wave signals output by a plurality of pulse wave sensors. 4 is a flowchart showing a process flow in the pulse rate measuring device. FIG. 1 is a diagram showing a plurality of frequency domain data sets each having a different period subjected to Fourier transform;

[Outline of Pulse Rate Measurement System S]
1 is a diagram showing an overview of a pulse rate measurement system S. The pulse rate measurement system S includes a pulse rate measurement device 1 and multiple pulse wave sensors 2 (2A, 2B, 2C). The pulse rate measurement system S is a system for measuring the pulse rate of a person (hereinafter referred to as a "user") based on at least one pulse wave signal detected by multiple pulse wave sensors 2 attached to multiple parts of the body of the user.

The pulse rate measuring device 1 is an electronic device having a processor, such as a computer, tablet, or smartphone. The pulse wave sensor 2 is, for example, a piezoelectric sensor, and outputs a pulse wave signal, which is an electrical signal indicating a change in pressure due to skin movement in synchronization with the pulse of the user wearing the pulse wave sensor 2. The pulse wave sensor 2 may be a sensor other than a piezoelectric sensor, such as a photoelectric or electrocardiographic sensor. The pulse wave signal output by the pulse wave sensor 2 is transmitted to the pulse rate measuring device 1, for example, via a wireless channel W or a cable.

The multiple pulse wave sensors 2 are attached to multiple locations where pulse waves can be detected, such as the user's elbow, wrist, chest, etc. The multiple pulse wave sensors 2 may be attached to multiple locations on the same location, such as multiple locations on the head. FIG. 1 illustrates a configuration in which multiple pulse wave sensors 2 are provided on the outside of the pulse rate measurement device 1, but the pulse rate measurement device 1 may be configured to have multiple pulse wave sensors 2 built in, and the multiple pulse wave sensors 2 may come into contact with multiple locations on the user when the user wears the pulse rate measurement device 1. In this case, the pulse rate measurement device 1 is, for example, a headgear-type device worn on the head.

Figure 2 is a schematic diagram showing pulse wave signals output by multiple pulse wave sensors 2. The dashed lines in Figure 2 indicate the upper and lower limits of the range in which the pulse rate measuring device 1 that receives the pulse wave signal can process the pulse wave signal. Figure 2(a) shows the pulse wave signal output by pulse wave sensor 2A, Figure 2(b) shows the pulse wave signal output by pulse wave sensor 2B, and Figure 2(c) shows the pulse wave signal output by pulse wave sensor 2C.

The pulse wave signal output by the pulse wave sensor 2 varies in amplitude and signal quality depending on the state of contact between the pulse wave sensor 2 and the user's skin. Figure 2(a) shows a pulse wave signal with an appropriate amplitude. Figure 2(b) shows a pulse wave signal with an excessively small amplitude. If there is insufficient contact between the pulse wave sensor 2 and the user's skin, it is conceivable that sufficient amplitude cannot be obtained as described above. Figure 2(c) shows a pulse wave signal with an excessively large amplitude.

The pulse rate measuring device 1 is characterized by selecting a pulse wave signal suitable for measuring the pulse rate from a plurality of pulse wave signals having different amplitudes and signal qualities, and measuring the pulse rate based on the selected pulse wave signal. Because the pulse rate measuring device 1 is configured in this manner, even if one of the plurality of pulse wave sensors 2 is poorly attached, the pulse rate measuring device 1 can measure the pulse rate with high accuracy based on the pulse wave signal output by a pulse wave sensor 2 that is well attached.

[Configuration of pulse rate measuring device 1]
3 is a diagram showing the configuration of the pulse rate measuring device 1. The pulse rate measuring device 1 has a communication unit 11, a display unit 12, a storage unit 13, and a control unit 14. The control unit 14 has a signal acquisition unit 141, a calculation unit 142, a signal conversion unit 143, a selection unit 144, and a pulse rate identification unit 145.

The communication unit 11 has a communication interface for acquiring pulse wave signals from the multiple pulse wave sensors 2. The communication unit 11 has, for example, a wireless communication controller or a wired communication controller. The communication unit 11 inputs the pulse wave signals received from the multiple pulse wave sensors 2 to the signal acquisition unit 141.
The display unit 12 is, for example, a display, and displays the pulse rate output by the pulse rate determination unit 145 .

The storage unit 13 has storage media such as a ROM (Read Only Memory), a RAM (Random Access Memory), and a hard disk. The storage unit 13 stores programs executed by the control unit 14. The storage unit 13 also stores the pulse wave signal acquired by the signal acquisition unit 141. The storage unit 13 stores the pulse wave signal in association with, for example, sensor identification information for identifying each of the multiple pulse wave sensors 2 and the date and time when the signal acquisition unit 141 acquired the pulse wave signal.

The control unit 14 is, for example, a CPU (Central Processing Unit), and functions as a signal acquisition unit 141, a calculation unit 142, a signal conversion unit 143, a selection unit 144, and a pulse rate determination unit 145 by executing a program stored in the memory unit 13.

The signal acquisition unit 141 acquires multiple pulse wave signals from multiple pulse wave sensors 2 attached to multiple positions on the body of the person whose pulse rate is to be measured, via the communication unit 11. The signal acquisition unit 141 inputs the acquired pulse wave signals to the calculation unit 142 and the signal conversion unit 143. The signal acquisition unit 141 may store the acquired pulse wave signals in the memory unit 13, and notify the calculation unit 142 and the signal conversion unit 143 of the pulse wave signal via the memory unit 13.

The calculation unit 142 calculates a provisional pulse period based on the time between at least any of the multiple adjacent peaks of the multiple pulse wave signals. FIG. 4 is a diagram for explaining the operation of the calculation unit 142. The calculation unit 142 identifies multiple peaks whose wave height values periodically maximize, such as P1, P2, and P3 in the pulse wave signal shown in FIG. 4, and calculates the time between adjacent peaks of the identified multiple peaks as the provisional pulse period. The calculation unit 142 may calculate the provisional pulse period by averaging the times between the multiple peaks.

The provisional pulse period calculated by the calculation unit 142 is notified to the signal conversion unit 143 and is used to determine the period of the pulse wave signal to be subjected to the Fourier transform when the signal conversion unit 143 performs the Fourier transform. When the calculation unit 142 detects multiple peaks, noise may be mistakenly identified as a peak, so the provisional pulse period may contain an error, but this error is considered to be of a size that is not problematic for the purpose of determining the period to be subjected to the Fourier transform. The calculation unit 142 may notify the pulse rate determination unit 145 of the calculated provisional pulse period.

The signal conversion unit 143 converts the multiple pulse wave signals acquired by the signal acquisition unit 141 into multiple frequency domain data by performing a Fourier transform on each of the multiple pulse wave signals. At this time, the signal conversion unit 143 may determine the period of the multiple pulse wave signals to be subjected to the Fourier transform based on the provisional pulse period notified by the calculation unit 142. For example, the longer the pulse period, the longer the period of the multiple pulse wave signals to be subjected to the Fourier transform is set by the signal conversion unit 143. By operating in this manner, the number of periods included in the pulse wave signal to be subjected to the Fourier transform can be kept within a certain range, thereby suppressing variation in measurement accuracy.

Figure 5 is a diagram showing an example of frequency domain data generated by signal conversion unit 143. The frequency domain data in Figure 5 is data obtained by signal conversion unit 143 performing a Fourier transform on the values of the pulse wave signal obtained by sampling the pulse wave signal at 200 Hz for 40 seconds. The horizontal axis of Figure 5 is frequency, and the vertical axis is signal level. The solid line in Figure 5 shows data obtained by performing a Fourier transform on a pulse wave signal with a pulse rate of approximately 90/min, and the dashed line shows data obtained by performing a Fourier transform on a pulse wave signal with a pulse rate of approximately 70/min. The dashed line in Figure 5 shows the noise level.

In the frequency domain data shown by the solid line, the first peak Pa1 is located at approximately 1.6 Hz, the second peak Pa2 is located at approximately 3.2 Hz, and the third peak Pa3 is located at approximately 4.8 Hz. The first peak Pa1 is the fundamental wave component of the pulse wave signal, and the second peak Pa2 and the third peak Pa3 are harmonic components of the pulse wave signal.

Similarly, in the frequency domain data indicated by the dashed line, there is a first peak Pb1 at approximately 1.2 Hz, a second peak Pb2 at approximately 2.4 Hz, and a third peak Pb3 at approximately 3.6 Hz. The first peak Pb1 is the fundamental wave component of the pulse wave signal, and the second peak Pb2 and third peak Pb3 are harmonic components of the pulse wave signal. In this way, since the frequency of the peaks in the frequency domain data differs depending on the pulse rate, it can be seen that the pulse rate can be determined by analyzing the frequency of the fundamental wave using the frequency domain data.

Returning to FIG. 3, the selection unit 144 will be described. The selection unit 144 selects, from the plurality of frequency domain data, frequency domain data in which the level of a predetermined frequency range or the signal-to-noise ratio (hereinafter referred to as "S/N ratio") is equal to or greater than a permissible value. The predetermined frequency range is a range that includes the main frequency components of the pulse wave signal, and is, for example, 1 Hz to 18 Hz. The selection unit 144 may determine the predetermined frequency range according to the user's condition. For example, when the selection unit 144 determines that the user has just exercised based on an input operation by the user, the selection unit 144 may set the predetermined frequency range to 2 Hz or greater.

The selection unit 144 may, for example, select frequency domain data in which the level of the fundamental wave component is equal to or greater than a tolerance value from among the multiple frequency domain data. The selection unit 144 may calculate the S/N ratio of the fundamental wave of each of the multiple frequency domain data, and select frequency domain data in which the calculated signal-to-noise ratio is equal to or greater than a tolerance value. The selection unit 144 may select frequency domain data in which the level of the fundamental wave component is maximum, or frequency domain data in which the S/N ratio is maximum, from among the multiple frequency domain data. In this case, the selection unit 144 specifies the S/N ratio by calculating the level of the fundamental wave component relative to the noise level in the frequency domain data.

The selection unit 144 may select frequency domain data in which the level or S/N ratio of a predetermined frequency range that includes pulse wave components in multiple frequency domain data and harmonic components of the pulse wave components within a predetermined order is equal to or greater than an allowable value. In this case, the selection unit 144 determines the S/N ratio by, for example, calculating the average signal level per unit frequency in a frequency range that includes components based on the pulse wave signal in the frequency domain data relative to the average noise level per unit frequency in the predetermined frequency range. By the selection unit 144 selecting frequency domain data based on the level or S/N ratio of such a frequency range, a pulse wave signal of good overall quality is selected even if the pulse wave signal is distorted, improving measurement accuracy.

When the selection unit 144 determines that there is no frequency domain data that satisfies the selection conditions, the selection unit 144 may display information on the display unit 12 indicating that the data cannot be acquired. The selection unit 144 may display the relationship between the quality of the pulse wave signal and the required quality on the display unit 12 in association with each pulse wave sensor 2. By the selection unit 144 displaying such information, it becomes possible for the user to determine which pulse wave sensor 2 needs to be adjusted in its attachment state.

Figure 6 is a diagram showing multiple frequency domain data corresponding to multiple pulse wave signals output by multiple pulse wave sensors 2. The solid line in Figure 6 is frequency domain data based on the pulse wave signal output by pulse wave sensor 2A, and the dashed line is frequency domain data based on the pulse wave signal output by pulse wave sensor 2B. As shown in Figure 6, there is a difference in the signal levels of the multiple frequency domain data depending on the degree of contact between the pulse wave sensor 2 and the body. In the example shown in Figure 6, the S/N ratio of the frequency domain data corresponding to pulse wave sensor 2A is greater than the S/N ratio of the frequency domain data corresponding to pulse wave sensor 2B, so the selection unit 144 selects the frequency domain data of pulse wave sensor 2A. The selection unit 144 notifies the pulse rate identification unit 145 that it has selected the frequency domain data of pulse wave sensor 2A.

The pulse rate identification unit 145 identifies the pulse rate based on the frequency domain data selected by the selection unit 144. The pulse rate identification unit 145 may identify the pulse rate based on the frequency of the fundamental wave in the frequency domain data, for example. As shown by the solid line in FIG. 4, when the frequency of the fundamental wave is 1.6 Hz, the pulse rate identification unit 145 identifies the pulse rate as 60×1.6=96 beats/second.

The pulse rate identification unit 145 may use the provisional pulse period calculated by the calculation unit 142 to identify the frequency of the fundamental wave. For example, the pulse rate identification unit 145 calculates a frequency corresponding to the provisional pulse period, and determines the frequency at which the signal level is maximum in the vicinity of the calculated frequency as the frequency of the fundamental wave. The pulse rate identification unit 145 may determine the frequency at which the signal level is maximum in a range less than twice the frequency of the fundamental wave corresponding to the provisional pulse period (i.e., less than the frequency of the first harmonic) as the frequency of the fundamental wave. The pulse rate identification unit 145 may determine the frequency at which the signal level is maximum within a predetermined range (for example, within a range of ±10%) based on the frequency corresponding to the provisional pulse period as the frequency of the fundamental wave. By operating in this manner, the pulse rate identification unit 145 can reduce the probability of erroneously detecting the frequency of the fundamental wave even when a noise frequency component is present.

[Processing flow in pulse rate measuring device 1]
Fig. 7 is a flowchart showing the flow of processing in the pulse rate measuring device 1. The flowchart shown in Fig. 7 starts from the point in time when the power supply of the pulse rate measuring device 1 is turned on.

When the pulse rate measuring device 1 is powered on, the signal acquisition unit 141 starts acquiring multiple pulse wave signals (S11). The calculation unit 142 calculates a provisional pulse period based on the multiple pulse wave signals acquired by the signal acquisition unit 141 (S12). The signal conversion unit 143 determines a period to be subjected to Fourier transformation based on the calculated provisional pulse period (S13), and generates multiple frequency domain data by Fourier transforming the multiple pulse wave signals over the determined period (S14).

Next, the selection unit 144 calculates the S/N ratio of each of the multiple frequency domain data (S15) and selects the frequency domain data with a relatively good calculated S/N ratio (S16). The pulse rate determination unit 145 determines the pulse rate based on the frequency domain data selected by the selection unit 144 (S17).

[Modification]
In the above explanation, an example has been given of the case where the signal conversion unit 143 determines the period to be subjected to the Fourier transform based on the provisional pulse period calculated by the calculation unit 142, but the signal conversion unit 143 may also determine a predetermined period to be subjected to the Fourier transform without using the provisional pulse period.

The signal conversion unit 143 may also update the period to be subjected to the Fourier transform based on the quality of the frequency domain data. For example, when the signal conversion unit 143 determines that the quality of the frequency domain data is at or above an acceptable level for a predetermined period of time or more and that the pulse wave signal is stable, the signal conversion unit 143 shortens the period to be subjected to the Fourier transform.

Specifically, the signal conversion unit 143 generates multiple frequency domain data by Fourier transforming multiple pulse wave signals over a first period, and if the quality of at least one of the multiple frequency domain data satisfies a predetermined condition, determines the period for which the multiple pulse wave signals are to be Fourier transformed to be a second period shorter than the first period. For example, the signal conversion unit 143 first generates frequency domain data by Fourier transforming a pulse wave signal sampled at a predetermined frequency (e.g., 200 Hz) over the first period of 40 seconds. If the S/N ratio calculated based on the generated frequency domain data is equal to or greater than a threshold value, the signal conversion unit 143 generates frequency domain data by Fourier transforming a pulse wave signal sampled at a predetermined frequency over a second period of 20 seconds, which is half the first period.

Figure 8 is a diagram showing multiple frequency domain data with different periods subject to Fourier transform. The solid line in Figure 8 shows frequency domain data when the period subject to Fourier transform of a pulse wave signal with a pulse rate of approximately 90 beats/second is 40 seconds, and the dashed line shows frequency domain data when the period subject to Fourier transform is 20 seconds. In this way, when it is determined that there is no significant difference in the quality of the frequency domain data even if the period subject to Fourier transform is shortened, the signal conversion unit 143 sets the period subject to Fourier transform in subsequent processing to the shortened period. By operating in this way, the signal conversion unit 143 can shorten the time required for Fourier transform, and therefore the time until the pulse rate identification unit 145 identifies the pulse rate.

The signal conversion unit 143 may determine that the period for which the multiple pulse wave signals are to be Fourier transformed is the second period when the quality of the frequency domain data selected by the selection unit 144 from among the multiple frequency domain data generated by Fourier transforming the multiple pulse wave signals over the first period satisfies a predetermined condition. By operating the signal conversion unit 143 in this manner, the period for which the Fourier transform is performed can be shortened based on the quality of the frequency domain data used by the pulse rate determination unit 145 to determine the pulse rate, thereby preventing a decrease in the accuracy of the pulse rate measurement due to shortening the period for which the Fourier transform is performed.

[Effects of the pulse rate measuring device 1]
As described above, signal conversion unit 143 converts each of the pulse wave signals into a plurality of frequency domain data by performing a Fourier transform on the pulse wave signals, and selection unit 144 selects, from the plurality of frequency domain data, frequency domain data having a level within a predetermined frequency range or a signal-to-noise ratio equal to or greater than an allowable value. Pulse rate identification unit 145 then identifies the pulse rate based on the frequency domain data selected by selection unit 144. By configuring pulse rate measurement device 1 in this manner, pulse rate identification unit 145 can identify the pulse rate using frequency domain data corresponding to a high-quality pulse wave signal, thereby improving the accuracy of pulse rate measurement.

Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the invention. For example, all or part of the device can be configured by distributing or integrating functionally or physically in any unit. In addition, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effect of the new embodiment resulting from the combination also has the effect of the original embodiment.

For example, FIG. 1 illustrates a case in which the pulse rate measuring device 1 acquires pulse wave signals from multiple pulse wave sensors 2 via wireless channel W, but multiple pulse wave sensors 2 and the pulse rate measuring device 1 may be housed in the same housing. Also, the above description illustrates a case in which the pulse rate measuring device 1 has a display unit 12 and the pulse rate measuring device 1 displays the measured pulse rate on the display unit 12, but the pulse rate measuring device 1 may transmit the measured pulse rate to an external device.

REFERENCE SIGNS LIST 1 Pulse rate measuring device 2 Pulse wave sensor 11 Communication unit 12 Display unit 13 Storage unit 14 Control unit 141 Signal acquisition unit 142 Calculation unit 143 Signal conversion unit 144 Selection unit 145 Pulse rate determination unit

Claims (4)

a signal acquisition unit that acquires pulse wave signals output from a plurality of pulse wave sensors attached to a plurality of positions on the body of a person whose pulse rate is to be measured;
a signal conversion unit that converts the pulse wave signals output by the plurality of pulse wave sensors into frequency domain data by performing a Fourier transform on the pulse wave signals;
a selection unit that selects, from the plurality of frequency domain data corresponding to the plurality of pulse wave sensors , the frequency domain data corresponding to any one of the pulse wave sensors having a level in a predetermined frequency range or a signal-to-noise ratio equal to or greater than a tolerance;
a pulse rate determination unit that determines a pulse rate based on the frequency domain data selected by the selection unit;
having
the signal conversion unit generates the plurality of frequency domain data by Fourier transforming the pulse wave signals output by each of the plurality of pulse wave sensors over a first period, and when the quality of at least one of the plurality of frequency domain data satisfies a predetermined condition, determines that the period over which the pulse wave signals output by each of the plurality of pulse wave sensors are to be Fourier transformed is a second period shorter than the first period. The signal conversion unit determines a period to be subjected to Fourier transform to be the second period when quality of the frequency domain data selected by the selection unit from among the plurality of frequency domain data satisfies the predetermined condition.
2. The pulse rate measuring device according to claim 1 . the selection unit selects frequency domain data in which a level or a signal-to-noise ratio in the predetermined frequency range that includes a pulse wave component and a harmonic component of the pulse wave component within a predetermined order in the plurality of frequency domain data is equal to or greater than a tolerance.
3. A pulse rate measuring device according to claim 1 or 2 . Computer,
a signal acquisition unit that acquires pulse wave signals output from a plurality of pulse wave sensors attached to a plurality of positions on the body of a person whose pulse rate is to be measured;
a signal conversion unit that converts the pulse wave signals output by the plurality of pulse wave sensors into frequency domain data by performing a Fourier transform on the pulse wave signals;
a selection unit that selects, from the plurality of frequency domain data corresponding to the plurality of pulse wave sensors , frequency domain data corresponding to any of the pulse wave sensors having a level in a predetermined frequency range or a signal-to-noise ratio equal to or greater than a tolerance;
a pulse rate determination unit that determines a pulse rate based on the frequency domain data selected by the selection unit;
A program for causing the device to function as a
The signal conversion unit converts the pulse wave signals output from the plurality of pulse wave sensors over a first period.
a program for generating the plurality of frequency domain data by Fourier transforming the pulse wave signal, and determining, when the quality of at least one of the plurality of frequency domain data satisfies a predetermined condition, that a period for which the pulse wave signals output by each of the plurality of pulse wave sensors are to be Fourier transformed is a second period shorter than the first period .

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