JPH07284483A - Method and apparatus for analyzing heartbeat fluctuation waveform - Google Patents

Abstract

PURPOSE:To exert the substantial effect of appearance frequency not amplitude on the spectrum analyzing result of an HF component becoming the investigation object of HRV in the analysis of heartbeat fluctuation waveform due to a heartbeat interval. CONSTITUTION:The original heartbeat fluctuation waveform is formed from a heartbeat interval and, further, the adjacent interval difference of the original heartbeat fluctuation waveform is calculated to form a relative displacement heartbeat fluctuation waveform. When the phase displacement heartbeat fluctuation waveform part exceeds a threshold value, it is displaced with the threshold value and, thereafter, the frequency component thereof is estimated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for analyzing a heartbeat fluctuation waveform, and more particularly to an R wave of an electrocardiogram (voltage pulse corresponding to contraction of a ventricle, a voltage pulse having high frequency and easy detection).
The present invention relates to a method and an apparatus for analyzing a heartbeat fluctuation waveform. The present invention is naturally applicable to the case of using data capable of extracting the heartbeat interval, such as a pulse wave and a peak value of a heart sound, as a substitute for the R wave of the electrocardiogram.

A heartbeat variability index (hereinafter referred to as HR) is analyzed by analyzing a heartbeat variability waveform generated from the R wave interval of the heartbeat.
V) may be abbreviated).

This HRV reflects the activity level of the sympathetic / parasympathetic nervous system, and has a low frequency (L) in its frequency component.
F) component (or frequency component of 0.05 to 0.15 cycle / beat called MWSA component), high frequency (HF) component (or frequency component of 0.15 to 0.45 cycle / beat called RSA component), etc. should be examined. It has been suggested that quantification of mental work load, mental work load, arousal level, and tension level can be performed, and it is known as a medically highly valuable index.

That is, the LF component is a component important because the blood pressure variability component reflecting the sympathetic nervous system has a low frequency, and its power is an increase in mental tension and an orthostatic stimulus ( It is recognized as increasing due to changes in posture). The HF component is so called because the respiratory variability component has a high frequency, and it is known that the HF component has a high value in a resting state or during sleep and tends to disappear due to an increase in tension. It is what

Therefore, whether the subject is at rest or not,
In other words, there is a demand for an HRV index that can easily determine whether or not the arousal level has decreased.

[0006]

2. Description of the Related Art A conventional method and apparatus for obtaining the power spectrum (or frequency component) value used for such HRV will be described below.

First, as shown in FIG. 4, biological electrodes 21 to 23 are attached to a human body 20, and the electric potential on the skin surface corresponding to the heart activity of the human body 20 is applied to the electrodes 21 and 23 and the electrodes 22 and 23 by an AC amplifier 24. The differential voltage is obtained, amplified, and sent to the A / D converter 25 as output signals A and B, respectively, where they are converted into digital signals, and then the arithmetic units 26
To the potential difference between the output signals A and B in FIG.
It is recorded as an electrocardiogram as shown in (1) and its power spectral density (PSD) is obtained.

FIG. 5 shows a procedure for generating a heartbeat fluctuation waveform (original heartbeat fluctuation waveform = RRI waveform). First, the R wave peak time is detected in FIG. As shown, the RR interval (hereinafter abbreviated as RRI) is measured from the R wave peak time. For example, as shown in FIG. 1A, the R wave peak interval RRI1 is 0.8.
If it is seconds, as shown in (2) of FIG.
Is set to "0.8".

The R-wave interval RRI thus generated according to the heartbeat is linearly interpolated as shown in FIG. 3 (3), and the horizontal axis is the number of beats and the vertical axis is the R-wave interval RRI. A heartbeat fluctuation waveform is generated.

Note that, hereinafter, this RRI waveform will be referred to as an original heart rate variability waveform in order to distinguish it from a heart rate variability waveform which has been subjected to various processes described later.

The RRI waveform generated in this manner is used to cut out a certain section as shown in the figure, and the sampling frequency is 5 Hz.
FIG. 6 shows the power spectrum density obtained by FFT calculation (fast Fourier transform calculation) or AR (autoregressive model).

As can be seen from the power spectrum estimation diagram of FIG. 6, most of the estimated power is a drift component having a center frequency of 0 Hz, and this is due to many of the original heartbeat fluctuation waveforms shown in FIG. 5 (3). This is because it contains an aperiodic component.

For this reason, as described above, it becomes difficult to detect the LF component or the HF component (peak power) which is the original object of study as the HRV.

Therefore, in order to solve such a problem, the inventor of the present invention proposes a method and apparatus for obtaining a frequency component result with high accuracy so that differences in HRV can be compared.
It has already been disclosed in 8861.

This will be explained in principle with reference to FIG. 7. First, the R wave intervals RRI1 to RRIn are calculated from the R wave time from the electrocardiogram as shown in FIG.

After the R-wave interval is extracted in this way, the difference between adjacent RRIs is calculated this time to generate the waveform shown in FIG. 2B (hereinafter sometimes referred to as RRI 'waveform).

The thus generated RRIn-RRI (n-
By generating the waveform of 1) for a long time as in the case of FIG. 5C, a waveform RRI having the horizontal axis as the number of beats as shown in FIG. 7C is obtained.

As a result, the characteristic obtained by the spectrum calculation becomes as shown in FIG. 8, and by this characteristic, the peak power positions of the LF component and the HF component under the condition that the heartbeat is non-stationary and the random transition is different. Can be estimated relatively easily.

[0019]

In the above-mentioned heartbeat fluctuation waveform, when the data such that the heartbeat intervals greatly differ during one beat like the heartbeat seen in the actual driving situation is used, A large error will occur in the analysis of the frequency component.

This will be explained with reference to FIG. 9. For example, from the RRI waveform having a large HF component shown in FIG.
When the RI 'waveform is generated, the waveform shown in (b) of the figure is generated. The RRI waveform is generated from the RRI waveform shown in (2) and (a) of the figure, in which the HF component is small but the heartbeat interval is large in one beat. Then, as shown in FIG.
Difference values for g and h (ed), (fe), (g-
f) and (h-g) also become large at the same time as shown in the figure.

Therefore, (1) (b) and (2) in FIG.
When (b) is used for frequency analysis or calculation of the HF component substitute index of HRV by dispersion in the interval (p) as shown in Japanese Patent Laid-Open No. 5-42129, that is, when the frequency component is estimated, the latter Although the HF component is smaller in the case of, the HF component ratio becomes larger than the former in calculation.

As described above, when the index corresponding to the HF component of HRV is originally considered, it is not the magnitude of the amplitude that is important but the frequency of its appearance. In the heartbeat fluctuation waveform, there is a problem that the frequency component cannot be accurately estimated in practice because it is affected by the magnitude of the amplitude.

Therefore, it is an object of the present invention to provide a heartbeat variability waveform analysis method and apparatus capable of substantially affecting not only the amplitude but the appearance frequency of the HF component analysis result which is the subject of HRV examination. And

[0024]

[Means and Actions for Solving the Problem] [1] Method of the present invention: From the heartbeat interval in FIG. 1, for example, from the original heartbeat fluctuation waveform (RRI waveform) having a large HF component shown in (1) and (a) of FIG. When the relative displacement heart rate variability waveform (RRI 'waveform) is generated by obtaining the difference between adjacent RRI waveforms as described above, the waveform shown in FIG. 9B is obtained as in the case of FIG.

On the other hand, from the RRI waveform shown in (2) and (a) in the figure, from the RRI waveform in which the HF component is small but the heartbeat interval is large in one beat, R
When the RI ′ waveform is generated, the waveform having a large amplitude value as shown by the dotted line in FIG. 11B is not generated, but is limited to the waveform shown by the solid line.

That is, when the RRI 'waveform exceeds the threshold value k, the RRI' waveform portion is replaced with the threshold value k and limited, and then the frequency component is estimated.

As a result, in the subsequent frequency analysis and frequency component estimation such as a substitute index of the HF component, it is possible to extract a value proportional to the frequency of the HF component rather than the amplitude, and the variance in the interval p is the same. The values in (1) and (a) in FIG. 11 are larger than those in (2) and (b) in FIG. 11, and an appropriate value can be obtained as a substitute index for the HF component of HRV.

[2] Device of the present invention: As a heartbeat fluctuation waveform analysis device according to the present invention for realizing the above-mentioned method of the present invention, a heartbeat pickup and an amplifier for amplifying an output signal of the pickup for a predetermined frequency band, It can be configured with a computing unit for computing the above method of the present invention.

That is, this arithmetic unit generates an original heartbeat fluctuation waveform from an A / D converter for converting the output signal of the amplifier into a digital signal and a peak value of the digital signal,
Furthermore, a relative displacement heartbeat variability waveform is generated by obtaining an adjacent difference between the original heartbeat variability waveforms, and when the relative displacement heartbeat variability waveform portion exceeds a threshold value, the relative displacement heartbeat variability waveform portion is replaced with the threshold value. After that, the frequency component is estimated.

[0030]

FIG. 2 shows an embodiment of a heartbeat fluctuation waveform analyzing apparatus according to the present invention. Basically, the AC amplifier section 24 and the A / D conversion unit are basically the same as the apparatus configuration shown in FIG. Although not shown, the input signal of the AC amplifier 24 is obtained from the biomedical electrode attached to the human body, which is composed of the unit 25 and the arithmetic unit 26.

In this embodiment, the AC amplifier section 24
Is constituted by a series circuit of the operation input amplifier 1 and the bandpass filter 2, and the bandpass filter 2 is set to a pass band of 8 to 18 Hz in order to extract only the R wave.

The A / D converter 25 includes an amplifier 3 connected to the bandpass filter 2 and a sample hold circuit 4.
And an A / D converter 5 and a buffer memory 6 in series.

Further, the arithmetic unit 26 includes a RAM 8 interconnected to a data bus 7 connected to the buffer memory 6, an arithmetic algorithm ROM 9, a CPU 10, and these RAMs 8.
And R without being connected to the CPU 10 and passing through the CPU 10.
DMA controller 1 for storing data in AM8
1 and a crystal oscillating circuit 12 for applying a constant clock signal to the CPU 10 and the DMA controller 11.

The A / D converter 25 includes the crystal oscillator circuit 1
A frequency divider 13 for dividing the frequency of the clock signal from 2 and giving it to the A / D converter 5 is provided. The DMA controller 11 includes a sample hold circuit 4 and an A / D converter 5.
Is also controlled.

FIG. 3 shows an embodiment of the processing procedure of the CPU 10 shown in FIG. 2. Hereinafter, the operation of the embodiment of FIG. 2 will be described with reference to the processing procedure of FIG. 3 and the waveform diagram of FIG. explain.

First, an output signal from a heartbeat pickup for detecting a heartbeat interval such as an R wave of an electrocardiogram, a pulse wave, and a peak value of a heart sound is amplified by a differential input amplifier 1 in an AC amplifier section 24 and a bandpass filter 2 is supplied. At, only R wave is extracted.

The R wave is amplified by the amplifier 3 in the A / D converter 25, sampled and held by the sample hold circuit 4 under the control of the DMA controller 11, and converted into a digital signal by the A / D converter 5. , From the buffer memory 6 via the data bus 7 into the CPU 10.

When the processing is started, the CPU 10 reads the R waveform data (step S1) and detects the R wave time (step S2).

From the R wave time thus obtained, FIG.
As shown in (2), the original heart rate variability waveforms RRI1 to RRI
n is calculated (step S3).

After extracting the R-wave interval RRI in this way, this time the difference between adjacent RRIs is calculated (step S
4), the waveform shown in FIG. 7B is generated.

RRI (n-1) -RRI generated in this way
By generating the waveform of n over a long period of time as in the case of FIG. 5C, for example, a waveform having the horizontal axis as the number of beats as shown in FIG.

When this converted data is RRI'n, this data RRI'n is stored in the RAM 8 (step S5).

Next, the CPU 10 sets the threshold value k (constant) shown in (1) (b) and (2) (b) of FIG. 1 (step S6).

As a result of limiting the RRI 'waveform to this value k, this threshold value k is a value at which frequency component estimation (HF component substitute index calculation by frequency analysis or variance) can be accurately performed corresponding to the actual HF component. It is obtained in advance by experiments or the like. The threshold value k may be automatically set or updated by an output from another device.

Here, after the initial value of the parameter i indicating the sample point position of the RRI 'waveform is set to "1" (step S7), the process is repeated until the parameter i> n (step S8). In step S9, the data RRI'i at the point i is read from the RAM 8.

Then, it is determined whether or not RRI'i≥k (step S10).

This determines whether or not the value of the sample point i of the RRI 'waveform exceeds a threshold value k indicating an abnormal heartbeat change which adversely affects the estimation of frequency components, as shown in FIG. As a result, if RRI′i ≧ k, the value of the RRI ′ waveform at the point i is replaced with the threshold value k and stored in the RAM 8 as being abnormal (step S11).

If RRI'i <k in step S11, the process proceeds to step S12 without executing step S11, increments the parameter i by "1" and repeats until i> n in step S8, i> When it becomes n, the RRI'n data is read from the RAM 8 and the process is transferred to a frequency analysis statistical processing unit (not shown) or the like.

[0049]

As described above, according to the heartbeat variability waveform analysis method and apparatus of the present invention, the original heartbeat variability waveform is generated from the heartbeat interval, and the adjacent interval difference between the original heartbeat variability waveforms is calculated. Generate a relative displacement heartbeat variability waveform obtained, when the relative displacement heartbeat variability waveform portion exceeds a threshold value, after replacing the relative displacement heartbeat variability waveform portion with the threshold value,
Since it is configured to estimate the frequency component, when determining the physiological state from the heartbeat variability waveform, the index that is worth studying in the variability component is frequency component estimation (frequency analysis such as spectrum analysis or simple variance etc.). It is possible to obtain an estimation result that is not easily influenced by the amplitude when extracting by type index calculation).

Therefore, for example, the LF / H of HRV which can be medically examined from the heartbeat data of the driver during actual road driving.
The F power can be estimated with high accuracy, and an alarm such as an accurate dozing driving can be issued.

[Brief description of drawings]

FIG. 1 is a waveform diagram for explaining the operation principle of a heartbeat fluctuation waveform analysis method and device according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a heartbeat fluctuation waveform analyzing apparatus according to the present invention.

FIG. 3 is a flowchart showing an example of calculation processing in a calculation unit of the heartbeat fluctuation waveform analyzing apparatus according to the present invention.

FIG. 4 is a block diagram showing a power spectrum measuring system as a general heart rate variability waveform analyzer.

FIG. 5 is a waveform diagram showing a conventional heart rate variability waveform generation procedure.

FIG. 6 is a graph diagram in which a power spectrum is estimated by a conventional example.

FIG. 7 is a waveform diagram for explaining the operation principle in the heartbeat fluctuation waveform analysis method and device according to Japanese Patent Application No. 5-189961.

FIG. 8 is a waveform diagram in which a power spectrum is estimated in a heartbeat fluctuation waveform analysis method and device according to Japanese Patent Application No. 5-189961.

FIG. 9 is a waveform diagram for explaining the problems of the conventional example.

[Explanation of symbols]

 20 Human Body 21-23 Biomedical Electrode 24 AC Amplifier 25 AD Converter 26 Arithmetic Unit 8 RAM 9 ROM 10 CPU In the drawings, the same reference numerals indicate the same or corresponding parts.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location A61B 5/04 312 R

Claims (2)

[Claims] 1. A relative heartbeat variability waveform is generated by generating an original heartbeat variability waveform from a heartbeat interval, and determining an adjacent interval difference between the original heartbeat variability waveforms. When exceeding, the relative displacement heartbeat fluctuation waveform portion is replaced with the threshold value, and then the frequency component thereof is estimated. 2. A heartbeat pickup, an amplifier for amplifying an output signal of the pickup in a predetermined frequency band, and an A for converting an output signal of the amplifier into a digital signal.
A D / D converter and an original heartbeat variability waveform are generated from the peak value of the digital signal, and an adjacent interval difference between the original heartbeat variability waveforms is obtained to generate a relative displacement heartbeat variability waveform. When the portion exceeds the threshold value, after replacing the relative displacement heart rate variability waveform portion with the threshold value,
A heartbeat variability waveform analysis device comprising: a calculation unit that estimates the frequency component.