JP2002112973A - Pulse rate measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse rate measuring instrument which can suppress a drop in calculation accuracy of pulse rates caused by noises by using a correlation operation. SOLUTION: When a pulse sensor 1 outputs a pulse signal of a subject, an amplifier circuit 12 amplifies the signal and a band-pass filter 13 removes noises of a prescribed frequency from the signal. Then, an A/D-converting section 14 performs A/D conversion on the signal and inputs the A/D-converted signal to a control section 2. The section 2 successively performs first and second sampling on the inputted pulse signal. Then the data obtained by the first sampling and the data obtained by the second sampling are subjected to the correlation operation and the pulse rate of the subject is calculated by using the results in the operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a pulse rate measuring device,
More specifically, the present invention relates to a pulse rate measuring device that calculates a pulse rate using a correlation operation.

[0002]

2. Description of the Related Art Conventionally, as a method for measuring a pulse rate, there is a method using an autocorrelation operation as disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 5-261107. To briefly explain the disclosed technology, a heartbeat signal detected by a sensor is sampled at a predetermined sampling rate, an autocorrelation function of the sampled heartbeat signal is calculated, and a pulse rate is obtained using the calculation result. is there. Furthermore, the pulse cycle is calculated based on the interval between points having a high degree of correlation obtained by the autocorrelation function.

In this case, the pulse cycle is calculated using the autocorrelation function. Therefore, even if sudden noise caused by body motion or the like is present in the heartbeat signal, the appearance interval of a high degree of correlation is high. The pulse rate can be calculated with high accuracy without much influence.

[0004]

However, when the pulse rate is calculated using the autocorrelation function as described above, sudden noise can be removed, but noise having the same waveform during the sampling period of the heartbeat signal. In the case where they are consecutive, a point indicating a high degree of correlation due to noise occurs. Therefore, there is a problem that the calculation accuracy of the pulse rate is reduced due to a point indicating a high degree of correlation due to the noise.

It is an object of the present invention to provide a pulse rate measuring device capable of suppressing a decrease in pulse rate calculation accuracy caused by noise.

[0006]

According to the present invention, there is provided a pulse detecting section for detecting a pulse, a pulse signal output circuit for outputting a pulse signal corresponding to the detected pulse, and a pulse signal output circuit for outputting the pulse signal within a first period. Correlation calculating means for calculating a degree of correlation between the pulse signal and the pulse signal output during a second period different from the first period, and a pulse rate for calculating a pulse rate based on the calculation result of the correlation calculating means Calculation means. Therefore, for example, even if the noise having the same waveform continues only in the pulse signal output in the first period, such noise is included in the pulse signal output in the second period. If not, the number of points exhibiting a high degree of correlation due to noise is reduced, and a decrease in pulse rate calculation accuracy can be prevented.

[0007] The correlation calculation means determines the first pulse signal output during the first period and the pulse signal output during the second period from the position where the first pulse signal is aligned with the first pulse signal. Calculating the degree of correlation when the pulse signal output during the period is shifted in the time lapse direction of the pulse signal and the reverse direction with respect to the pulse signal output during the second period. Thus, for example, even if a pulse signal not affected by noise is present only in the first half of the pulse signal output during the first period, the pulse signal is reliably correlated with the portion not affected by noise. Calculation can be done,
The points showing high correlation due to noise are reduced,
It is possible to prevent a reduction in the calculation accuracy of the pulse rate.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below based on an embodiment shown in the drawings.

In FIG. 1, the pulse detecting section 1 includes a pulse sensor 11, an amplifier circuit 12, a band-pass filter 13, and an A / D converter 14. As the pulse sensor 11,
For example, a known pulse sensor such as a photoelectric pulse sensor or a piezoelectric pulse sensor is used. The control unit 2 serving also as a correlation calculation unit and a pulse rate calculation unit includes a CPU, a ROM, a RAM, and the like.
Various operations are controlled according to operation programs stored in the ROM. The pulse rates bpm (1) to bpm (5) for the past five times are stored in the RAM in the control unit 2. The display unit 3 displays the pulse rate per minute (bp) calculated by the control unit 2.
m) is displayed.

Next, the operation will be described with reference to FIG.

When the pulse sensor 11 detects a pulse and outputs a pulse signal, the pulse signal is amplified by an amplifier circuit 12, noise of a predetermined frequency is removed by a band-pass filter 13, and an A / D converter 14 A / D conversion is performed and input to the control unit 2.

The control unit 2 receives a first pulse signal from the input pulse signal.
Is performed. Specifically, for example, 20m
Sampling is performed for 4 seconds (first period) at a sampling period of s, and the sampled pulse signal data is stored in the first storage unit in the RAM. In this case, the number of sampled data is 200. Hereinafter, the data stored in the first storage unit is referred to as X group data (X _{1 to} X ₂₀₀ ).

When the first sampling process is completed, a second sampling process is performed. Specifically, for example, 20
Sampling is performed for 4 seconds (second period) at a sampling period of ms, and the sampled pulse signal data is stored in the second storage unit in the RAM. Also in this case, the number of sampled data is 200. Hereinafter, the data stored in the second storage unit is referred to as Y group data (Y ₁ to Y ₂₀₀ ). As described above, since the second sampling process is performed after the first sampling process is completed, pulse signals in different periods are sampled.

When the first and second sampling processes are completed, the pulse signal data sampled based on the maximum value of the sampled pulse signal data is shifted down so that the calculation result does not overflow in the correlation operation described later.

FIG. 2 shows the operation up to this point as pre-data processing (step 2a).

When the pre-data processing is completed, the mutual degrees C _j and D _j of the X group data and the Y group data are obtained from the following equations (1) and (2) (steps 2b and 2c).

[0017]

(Equation 1)

[0018]

(Equation 2) Note that n = 200 (the number of sampling data), j = 1,
2 ... 198 and 199.

In this embodiment, the accuracy of the correlation result is improved by performing two cross-correlation calculations of C _j and D _j . Hereinafter, this point will be described. C _j is C ₁ = (X ₁ × Y ₂ + X ₂ × Y ₃ + X ₃ × Y ₄ +... + X ₁₉₉ × Y ₂₀₀ ) / 199 C ₂ = (X ₁ × Y ₃ + X ₂ × Y ₄₎ + X ₃ × Y ₅ +... + X ₁₉₈ × Y ₂₀₀ ) / 198..., That is, the head of the X group data and the Y group data (X
₁ , Y ₁ ), the X-group data (X ₁ ) is used to perform a correlation operation when shifting the X-group data with respect to the Y-group data in the time elapse direction of the pulse signal (sampling time direction) with respect to the Y-group data. To X ₂₀₀ ) and Y group data (Y _{1 to} Y
₂₀₀ ) is less likely to be reflected in the correlation operation. Therefore, for example, when the Y group data (Y _{1 to} Y ₂₀₀ ) is normal pulse data, noise is put on the first half of the X group data (X _{1 to} X ₂₀₀ ) due to the influence of body movement or the like. If normal pulse data exists only in the latter half, it becomes difficult for a peak corresponding to the pulse to appear. Conversely, D
_j is D ₁ = (Y ₁ × X ₂ + Y ₂ × X ₃ + Y ₃ × X ₄ +... + Y ₁₉₉ × X ₂₀₀ ) / 199 D ₂ = (Y ₁ × X ₃ + Y ₂ × X ₄ + Y ₃ × X ₅ +... + Y ₁₉₈ × X ₂₀₀ ) / 198..., That is, the head of the X group data and the Y group data (X
₁ , Y ₁ ), the X-group data is used to perform a correlation operation when shifting the X-group data with respect to the Y-group data in the direction opposite to the time elapse direction (sampling time direction) of the pulse signal with respect to the Y-group data. second half of the first part and the Y group data (Y ₁ to Y ₂₀₀₎ of (X ₁ ~X ₂₀₀₎ is less likely to be reflected in the correlation operation. Therefore, for example, when the Y group data (Y _{1 to} Y ₂₀₀ ) is normal pulse data, the X group data (X _{1 to} X ₂₀₀ )
If the noise is put on by the influence of body motion etc. in the latter half part and normal pulse data exists only in the first half part,
It becomes difficult for a peak corresponding to the pulse to appear. Such a problem is peculiar to the cross-correlation function which does not occur in the autocorrelation function disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 5-261107.

In this example, by performing two operations, C _j and D _j , each complementing the shortcomings of the other's operation,
The detection accuracy of the peak according to the pulse is improved.

FIG. 3 is a correlation diagram showing the calculation result of C _j or D _j .

When the calculation of C _j and D _j is completed, effective peak points at C ₁ to ₁₉₉ and D ₁ to ₁₉₉ are obtained, respectively. In the present example, the condition for finding an effective peak point is that after successively up more than a predetermined threshold value, it is continuously down more than a predetermined threshold value. However, if there is a peak that does not satisfy the above conditions, if the peak is lower than the immediately preceding peak point, it is regarded as a peak due to noise and ignored.
When the peak is higher than the immediately preceding peak point, it is regarded as a valid peak point.

When the effective peak points of C ₁ to ₁₉₉ and D ₁ to ₁₉₉ are respectively obtained, the interval between the adjacent effective peak points is obtained, and is set as P1 _(X) P2 _(Y) (step 2 _).
d).

Subsequently, invalid peak intervals are excluded from P1 _(X) (step 2e). As an exclusion method, for example, a peak not within ± 20% of the average of all peak intervals in P1 _(X) is excluded as an invalid peak interval affected by noise.

After the elimination of the invalid peak interval, P1
Pulse rate bpm based on peak interval remaining as _(X)
(A) (1 minute pulse rate) is obtained (step 2f).
Specifically, it is calculated by the formula bpm (A) = 1 min / ((average value of P1 _(X) ) × 20 ms).

Subsequently, invalid peak intervals are excluded from P2 _(Y) (step 2g). This operation is performed in the same manner as in step 2e described above. The difference from step 2e is that the target data is not P1 _(X) but P2 _(Y) .

When the elimination of invalid peak intervals from P2 _(Y) is completed, the pulse rate bpm (B) (pulse rate per minute) is obtained based on the peak intervals remaining as P2 _(Y) (step 2h). Specifically, bpm (B) = 1 min /
(Average value of P2 _(Y) ) × 20 ms.

Subsequently, the past five pulse rate bpm values bpm (1) to bpm stored in the RAM of the control unit 2
(5) Median bpm and bpm (A) and bpm
(B) is compared, and one of bpm (A) and bpm (b) that is closer to the central value bpm is determined as the confirmed bpm value (step 2i). This confirmed bpm value becomes the current pulse measurement value and is displayed on the display unit 3.

When the determined bpm value is obtained, the RA
The past five pulse rate bpm values bpm stored in M
(1) to update bpm (5) (step 2j).
Specifically, the bpm (2) currently stored in the RAM
Bpm (5) is moved to bpm (1) to bpm (4), and the confirmed bpm value is copied to bpm (5).

As described above, the calculation result of the cross-correlation calculation for calculating the degree of correlation between the pulse signal output during the first period and the pulse signal output during the second period different from the first period is obtained. Since the pulse rate is calculated based on the pulse rate, for example, even if the same noise is continuously generated only in the pulse signal output in the first period, the same as the pulse signal output in the second period is obtained. If such noise is not present, points indicating a high degree of correlation due to the noise are reduced, and it is possible to prevent a decrease in pulse rate calculation accuracy.

In the above description, the sampling period is set to 20
Although ms and the sampling period are set to 4 seconds, the sampling period and the sampling period are not limited thereto, and can be changed as appropriate.

The conditions for finding valid peak points and the conditions for excluding invalid peak intervals are not limited to those described above, and can be changed as appropriate.

In the above example, bpm (A) and bp
m (b) is separately obtained, and the pulse rate closer to the past pulse rate is selected and used as the pulse rate measured this time.
Instead of separately calculating (A) and bpm (b), instead of P1 _(X) , P2 _(Y) may be combined to obtain an average value, from which the pulse rate may be calculated.

[0034]

According to the present invention, a cross-correlation calculation for calculating a degree of correlation between a pulse signal output during a first period and a pulse signal output during a second period different from the first period is performed. Since the pulse rate is calculated based on the calculation result, even if a similar noise is continuously generated only in the pulse signal output in the first period, for example, the pulse signal is output in the second period. If similar noise is not included in the pulse signal, the number of points indicating a high degree of correlation due to the noise is reduced, and it is possible to prevent a decrease in the calculation accuracy of the pulse rate.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of FIG. 1;

FIG. 3 is an explanatory diagram showing a cross-correlation calculation result in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pulse detection part 2 Correlation calculation means, pulse rate calculation means

Claims (2)

[Claims] 1. A pulse detecting section for detecting a pulse and outputting a pulse signal corresponding to the detected pulse, and a second period different from the first period and the pulse signal output within a first period A pulse rate measuring device comprising: a correlation calculating means for calculating a degree of correlation with the pulse signal output in the apparatus; and a pulse rate calculating means for calculating a pulse rate based on a calculation result of the correlation calculating means. . 2. The pulse calculator according to claim 1, wherein the correlation calculation unit aligns the head of the pulse signal output during the first period with the head of the pulse signal output during the second period. When the pulse signal output during the first period is shifted in the time lapse direction of the pulse signal and the reverse direction from the pulse signal output during the second period from the position A pulse rate measuring device for calculating a degree of correlation.