JP2001333890A - Method of computing pulse rate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To figure out a representing value for a period of pulse without being affected by noise. SOLUTION: When pulse rate is figured out by obtaining a period of pulse from output by a pulse sensor which detects pulse, the pulse rate of a period, when there is no signals considered as a pulse, is presumed by using a representing value for a period of the pulse which is calculated from a period of the pulse obtained before. An auto-correlation function for the pulse signals during a pre-determined period is figured out. When the first peak value going into the positive direction is greater than a pre-determined threshold value, the period of the pulse during the period is taken as a representing value for the period of the pulse. Influence caused by noise is avoided by calculating the representing value for the period of the pulse using the auto-correlation function.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse rate calculating method capable of calculating a pulse rate when noise due to body motion or the like is mixed.

[0002]

2. Description of the Related Art When a pulse rate is measured in a non-invasive manner, a signal which can be regarded as a pulse wave is extracted from the output of a pulse sensor, and the time of occurrence of each pulse is sequentially stored. Calculating the pulse wave period from the above, and obtaining the pulse rate from the period.

In this case, there is no problem as long as the pulse wave can be reliably detected. However, in practice, a signal that can be temporarily regarded as a pulse wave cannot be obtained due to noise due to body movement. In this case, an accurate pulse rate cannot be obtained unless the cycle is calculated in a manner that complements the pulse wave that should exist.

Here, Japanese Patent Application Laid-Open No. 9-173308 discloses a method for estimating a pulse rate during a period in which a signal that can be temporarily regarded as a pulse wave is not obtained, based on the pulse wave period up to that time. It is shown that the range of the pulse wave cycle is limited, and the cycle up to a signal that may be a pulse wave is estimated from a representative pulse wave cycle value obtained based on the previous pulse wave cycle.

In the above publication, the average value of several recent pulse wave periods excluding a period in which a signal that can be regarded as a pulse wave is not obtained and not including this period is adopted as a pulse wave period representative value. It is shown. Here, the period during which a signal that can be regarded as a pulse wave is not obtained is a case in which one or more pulse wave periods that do not enter a region where the constant rate is increased or decreased from the pulse wave period representative value continue.

[0006]

In this case, if the representative value of the pulse wave cycle is correct, the pulse rate calculated on the basis thereof will be almost accurate. Have the following problems:

That is, when noise is mixed in the pulse wave signal due to body movement, a state in which the pulse wave cycle representative value does not always enter a region where the constant rate is increased or decreased does not always occur. May continue to enter the increased or decreased area,
As a result, the pulse wave cycle may gradually increase. M1 to M4 in FIG. 4 show this case, and M3 and M4 are not due to the original pulse wave but due to noise.

When such a state occurs, when the signals M5 to M7, which are the original pulse waves, are obtained again, the value representative of the pulse wave period calculated for calculating the pulse rate becomes the true pulse wave. In the example shown in FIG. 4, the pulse wave of M6 may be ignored in practice because the value is far from the wave period. At this time, an accurate pulse rate cannot be obtained. In other words, in estimating the pulse rate during the period when a signal that can be regarded as a pulse wave signal could not be obtained,
Since the pulse wave cycle representative value itself, which is the basis for the estimation, has been affected by noise, there is a case where an accurate pulse rate cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a purpose thereof is to calculate a pulse wave cycle representative value without being affected by noise. An object of the present invention is to provide a pulse rate calculation method capable of calculating a pulse rate.

[0010]

According to the present invention, when a pulse rate is calculated by obtaining a pulse wave period from an output of a pulse sensor for detecting a pulse wave, it is determined that there is no signal which can be temporarily regarded as a pulse wave. The pulse rate during the specified period is estimated using the pulse wave cycle representative value calculated from the pulse wave cycle determined before that, and the autocorrelation of the pulse wave signal during the predetermined period is calculated. A first feature is that a function is calculated, and when the first peak value in the positive direction is larger than a predetermined threshold value, the pulse wave cycle within the period is used as the pulse wave cycle representative value. The autocorrelation function of the pulse wave signal for a predetermined period is calculated, and the first peak value in the minus direction is smaller than a predetermined threshold value, and the first peak value in the positive direction is smaller than a predetermined threshold value. If greater, within the above period With the pulse wave period and has a second feature in that with the pulse wave period representative value.

Since the pulse wave cycle representative value is calculated using the autocorrelation function, the influence of noise can be prevented, and an erroneous pulse rate is calculated based on an erroneous pulse wave cycle representative value. Can be prevented from occurring.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment. The equipment for measuring the pulse rate and the method of calculating the basic pulse rate are not described because they are basically the same as those described in the above publication,
Only a method of calculating a pulse wave cycle representative value serving as a basis for calculating a pulse rate during a period in which it is determined that there is no signal that can be temporarily regarded as a pulse wave will be described. First, as shown in FIG. Initial values are determined in advance. As the initial value, for example, the pulse rate per minute is expected to be 70, so a value based on this is set. Then, the pulse wave signal data for a predetermined time is read, an autocorrelation function is calculated, and then the pulse wave cycle is interpolated as necessary based on the pulse wave cycle representative value. Further, when the first peak value on the plus side of the autocorrelation function (see FIG. 2B) is larger than a predetermined value, it is determined that noise is not mixed in the pulse wave signal, and the pulse wave signal during that period is determined. The representative value of the pulse wave cycle is rewritten using the pulse wave cycle of the wave signal as a representative value, and the next pulse wave signal data is read.

The pulse wave signal data to be read at one time is calculated to have an autocorrelation function and has a length sufficient for a peak around one period of the pulse wave signal, for example, 3 seconds or more. Furthermore, in order to calculate the peak value of the autocorrelation function, the autocorrelation coefficient is calculated at sufficiently small time intervals.

FIG. 3 shows another example. Basically the same as the above, but when evaluating the representative value of the pulse wave period from the autocorrelation function, the first peak value on the plus side (see FIG. 2B) is a predetermined value. If it is larger and the first peak value on the minus side of the autocorrelation function (see a in FIG. 2) is smaller than a predetermined value, it is determined that the pulse wave signal contains no noise. Judgment is made, the pulse wave cycle of the pulse wave signal in that period is adopted as a representative value, the representative value of the pulse wave cycle is rewritten, and the next pulse wave signal data is read. In this case, the possibility of noise mixing can be more reliably eliminated than that shown in FIG.

[0015]

As described above, according to the present invention, in the calculation method for calculating the pulse rate in a period in which a signal that can be temporarily regarded as a pulse wave was not obtained based on the pulse wave cycle representative value obtained in advance, Since the pulse wave cycle representative value is determined using the correlation function, a pulse wave cycle representative value that is not affected by noise can be obtained, and therefore, an accurate pulse rate can be obtained. .

In using the autocorrelation function, the evaluation is performed with reference to not only the peak value on the plus side but also the peak value on the minus side, so that the pulse wave cycle representative value can be calculated as more accurate. Accordingly, a more accurate calculation of the pulse rate can be performed.

[Brief description of the drawings]

FIG. 1 is a flowchart of a main part according to an example of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a peak value in an autocorrelation function.

FIG. 3 is a flowchart of a main part in another example.

FIG. 4 is a time chart showing an example of a pulse wave signal mixed with noise.

FIG. 5 is a time chart showing an example of a pulse wave signal in which noise is not mixed.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akihiro Michimori 1048 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Works, Ltd. F term (reference) 4C017 AA02 AA10 BC16 FF05

Claims (2)

[Claims] When calculating a pulse rate by obtaining a pulse cycle from an output of a pulse sensor for detecting a pulse wave, the pulse rate during a period in which it is determined that there is no signal that can be temporarily regarded as a pulse wave is calculated by:
In a method of calculating a pulse rate to be estimated using a pulse wave cycle representative value calculated from a pulse wave cycle obtained before that,
Calculate the autocorrelation function of the pulse wave signal for a predetermined period, and when the first positive peak value is larger than a predetermined threshold, the pulse wave period representative value with the pulse wave period within the period. A method of calculating a pulse rate. 2. When calculating a pulse rate by obtaining a pulse cycle from an output of a pulse sensor for detecting a pulse wave, a pulse rate during a period in which it is determined that there is no signal that can be temporarily regarded as a pulse wave is calculated by:
In a method of calculating a pulse rate to be estimated using a pulse wave cycle representative value calculated from a pulse wave cycle obtained before that,
Calculate the autocorrelation function of the pulse wave signal for a predetermined period, and when the first peak value in the negative direction is smaller than the predetermined threshold value and the first peak value in the positive direction is larger than the predetermined threshold value A pulse wave period within the period, the pulse wave period representative value being used as the pulse wave period representative value.