JP2003190110A - Autonomic nervous system function indicator based on phonocardiogram - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an autonomic nervous system condition evaluating means inexpensive and easy to use. <P>SOLUTION: In a method and a device for measuring the heart rate variation (HRV), computer processing is applied to recorded cardiac sound and this is analyzed to acquire various components characterizing the HRV. The HRV is measured on the basis of cardiac sound signals easily collectable by a microphone easy to attach on a patient or a stethoscopical apparatus to be used for stethoscopy so that speedy diagnosis and information transmission can be performed. The diagnosed result possible to occur is reduced and therefore the rate of survival of the patient is improved. <P>COPYRIGHT: (C)2003,JPO

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 monitoring the autonomic nervous system, and more particularly, heart sound recording (cardiogram).
And apparatus for measuring heart rate variability (HRV) based on

[0002]

2. Description of the Related Art The Autonomic Nervous System (ANS) controls the function of each organ and the biological homeostasis such as heartbeat, digestive absorption, respiration and blood flow, and in many cases, these are voluntarily controlled. Not not. Such involuntary movements are controlled by the reciprocal action of two parts of the autonomic nervous system, namely the sympathetic and parasympathetic parts. In the normal environment, many organs are stimulated by both of these departments to perform proper organ functions and meet the demands of life. The imbalance of the autonomic nervous system causes problems such as coronary heart disease, hypertension, dyspepsia, and sudden death.

A number of techniques have been developed for the assessment of the state of the autonomic nervous system and have shown good results. These include changes in heart rate associated with deep breathing, response to the Valsava test, sweating motor function, orthostatic blood pressure recording, cold pressure test and biochemical test. However, these techniques are mostly invasive and use expensive diagnostic equipment. Therefore, these techniques are generally not suitable for application.

It is believed that the heartbeat modulation pattern is closely related to the modulation of the autonomic nervous system. Heart rate modulation (HR
V) has been developed as a functional index of the autonomic nervous system. H
RV is associated with changes in beating intervals in heartbeat. H as the heart accelerates or decelerates with each precordial breath.
RV is a measure to measure changes in beating time intervals. Among various autonomic nervous system evaluation techniques, HRV is one of the important developments because it is non-invasive, and it is a groundbreaking development. Moreover, since the equipment used for this technique is inexpensive, it can be widely applied. Furthermore, animal and clinical studies have shown that HRV
Accurately reflects the behavior and balance of the sympathetic and parasympathetic nerves.

Adults at rest have about 70 heart beats per minute. This rhythmic beat is caused by the coupling of electrical events between cardiomyocytes, including myocardial cells, nodule cells and conducting cells. The heart is stimulated by both the sympathetic and parasympathetic parts of the autonomic nervous system, and they work together to perform appropriate functions under normal conditions. However, when the body is stressed, the sympathetic nervous system becomes dominant and the heart rate and blood pressure rise. When an emergency passes by, the parasympathetic nervous system controls and reduces the heart rate. Heart rate is maintained by frequent and detailed nervous system control with complex dynamic feedback. Therefore, the heart rate of a healthy individual has very little periodic fluctuation that occurs every 10 seconds or every 3 seconds.

Recent advances in electrical engineering have made it possible to assess changes in heart rate by frequency domain analysis based on mathematical processing of data obtained from an electrocardiogram (ECG). FIG. 1 is a flow diagram illustrating a conventional method for evaluating the change in heart rate. As shown in FIG. 1, first, an electrocardiogram (ECG) is taken from a subject.
The ECG signal is then amplified, filtered and digitized. Then, the ECG signal is processed using the computer program for HRV analysis. The computer first detects the peaks of all digital ECG signals and predicts the spacing between the two peaks. The frequency domain measurements are further quantified using the Fast Fourier Transform (FFT) non-variable method.

Researchers have found that based on frequency analysis, HRV can be characterized as two main components, a high frequency (HF) component and a low frequency (LF) component.
The high frequency components are equivalent to respiratory sinus arrhythmias and are thought to represent the effects of vagal control on heart rate. Although the exact origin of the low frequency component is unknown, it is thought to be related to the action of blood vessels or the baroreflex. Further, some researchers divide this low frequency component into a low frequency component and an extremely low frequency component.

It has been well documented that HRV is clinically effective and meaningful in reflecting many physiological functions. Many researchers have shown that high frequency components or total output (TP) represent control of heart rate by the paraautonomic nervous system, and LF / H
It is considered that the F ratio reflects the balance of the autonomic vagus nervous system or the autonomic nervous system modulation. Low HRV values are considered as indicators of increased intracranial pressure and are associated with aging. HF levels are diminished in diabetic neuropathy, while the LF / HF ratio is sensitive to postural changes and distress. Studies on the human body have shown that LF disappears in the state of brain death, and thus can be used as a prognostic means for predicting the condition of a patient in an intensive care unit. Framingh
According to a recent study by Am, assuming that the HRV value of the aging person is reduced by one standard deviation value, the HRV value of the dying individual is about 1.7 times lower than that of the normal person.

Although HRV holds promise for the prediction of all pathological conditions, it remains an unsolved measurement technique. Although the periodical change of the heart rate determined by frequency analysis of the ECG signal can indirectly evaluate the autonomic nervous system, it is not easy to acquire the ECG signal. To obtain information on HRV, ask the patient for an ECG.
It is necessary to wear the module to obtain the heartbeat interval and measure the change in heart rate from this value. To obtain an electrocardiographic signal, it is also necessary to attach a large number of electrodes to various parts of the body.

HRV changes respond to many common but fatal illnesses, such as those with coronary heart disease and hypertension, with methods and devices readily applicable to the patient. At the same time, rapid diagnosis and transmission of information reduce the possibility of possible diagnosis results, resulting in improvement of the survival rate of patients.

[Means for Solving the Problems]

Therefore, the present invention is based on the change of heart rate (HRV).
The present invention provides a method and apparatus for monitoring the autonomic nervous system by measuring the above, and can evaluate the heartbeat signal of the heart more easily and easily.

Therefore, the present invention provides a heart rate change monitoring device which is easy to operate, portable, and easy for the user to use. The HRV measuring device of the present invention includes a microphone for collecting a voice signal of the heart, and further includes an amplifier,
It is equipped with a filter and an A / D converter for processing and digitizing audio signals. The device is also equipped with a computer that analyzes the audio signal and produces meaningful physiological and clinical results. The analysis results can be viewed online by the user during the test or can be transmitted to another computer system for offline verification after the test is complete.

The present invention provides a method of measuring HRV of a subject, in which a heart sound is collected for 3 to 5 minutes by placing a microphone near the heart of the subject. The heart sound signal is amplified, filtered, and transmitted to the A / D converter.

The beating interval is determined by analyzing the digital audio signal using a computer. Parameters such as amplitude and duration of all peak values are obtained, and their average value and standard deviation are calculated, and these are used as standard patterns (plurality), and compared with the standard individually for the subsequent heart rate. Further, the spectral intensity density is estimated based on the fast Fourier transform (FFT), and subsequently, the low frequency (LF) and the high frequency (H
F), total output value and integral value in standard frequency domain including LF / HF. The obtained parameters are index-transformed.

Since the HRV of the present invention is based on the phonocardiogram easily obtained by mounting a microphone on the patient, the pathological condition of the patient can be easily evaluated and diagnosed. Further, the HRV values corresponding to the phonocardiogram can be transmitted to the computer system for off-line verification after the examination, even if collected at the patient's home.
The rapid diagnosis and transmission of information reduces possible diagnostic results and improves patient survival.

It is to be understood that the foregoing general description as well as the following detailed description are for purposes of illustration and are intended to further describe the invention as claimed.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows the change in heart rate (HRV) according to the present invention.
4 is a flow diagram showing a method for evaluating The HRV of this invention is obtained from the recording of heart sounds (cardiogram). As shown in FIG. 2, use a microphone for 3 minutes or 5
Collect heart sound signal for minutes. The microphone is attached to, for example, the left chest of the individual to be measured. A hearing device used for auscultation can also be used to collect the heart sound signal. The heart sound signal is amplified, bandpass filtered, and the processed signal is further A / D converted at a sampling rate of 1024 Hz or 2048 Hz. Data acquisition and subsequent analysis are performed by a computer device including a microchip used for a portable computer, a personal digital device, a mobile phone, a wristwatch and the like. The computer system must also have a microprocessor and suitable storage. The digitized heart sound signal is
Online analysis is possible during the inspection and at the same time it can be stored in a removable hard disk for offline verification after the inspection.

Still referring to FIG. 2, the digitized heart sound signal is analyzed to predict beat intervals. A spike detection algorithm is applied to detect all digital echogram peaks. The peak time of each beat is defined as the beat occurrence time point, and the time interval between the two peaks is calculated as the beat interval time between the current beat and the next beat. Parameters such as amplitude and duration of all peaks are measured, and their average value and standard deviation value are calculated as a standard pattern. Determine each beat by comparing it to the standard. If any of the peak interval values is three times or more the standard deviation value, the measured value is regarded as an error and is excluded. FIG. 3 is a diagram showing a phonocardiogram and corresponding heart beat intervals when a subject is examined for 5 minutes according to the method of the present invention.
The dotted line on the phonocardiogram is automatically identified by the computer system and indicates the peak of the heartbeat. Figure 4
FIG. 3 shows a phonocardiogram and corresponding heart beat intervals when a subject is examined for 5 minutes according to the method of the present invention. The dotted line on the phonocardiogram is automatically identified by the computer system and indicates the peak of the heartbeat.

Returning to FIG. 2, the description will be continued. Effective peak interval time values are subsequently sampled again at a rate of 7.11 Hz and inserted to provide continuity in the time domain. After that, the analysis in the frequency domain is performed using the fast Fourier transform (FFT). Hamming by eliminating the DC component of the signal
Attenuate the leakage effect using windows. 288
Calculate the signal output spectral distribution based on the Fast Fourier Transform every second or every 2048 data points. For the obtained signal output spectrum, sampling and Ha
The attenuation component due to the mming window is corrected.

The heart sound signal output spectrum has a low frequency (L
F 0.04 to 0.15 Hz) and high frequency (H
F 0.15-0.40 Hz), full power (TP), and standard frequency domain parameters including ratio of low frequency to high frequency (LF / HF ratio). LF, HF, TP and LF
The / HF ratio corrects the skewness of the distribution by exponential conversion.
FIG. 5 shows various frequency domain parameters characteristic of HRV obtained based on the analysis of the information shown in FIG. As shown in FIG. 5, the clinical subject's 5-minute phonocardiographic compression locus, corresponding beat interval time, signal output density, H
F, LF, HF / LF are illustrated. FIG. 6 is a diagram showing the correlation between various frequency domain parameters characteristic of HRV obtained by the method of the present invention and by the conventional method for 10 clinical subjects. All parameters show favorable correlations, with correlation coefficient (r) greater than 0.93.

[0021]

The HRV of the present invention can be easily evaluated and diagnosed because the HRV of the present invention is obtained from the phonocardiogram easily obtained by mounting the microphone on the patient. Further, the phonocardiogram and its corresponding HRV values can be transmitted to the computer system for off-line verification after the examination, even if collected at the patient's home.
The rapid diagnosis and transmission of information reduces possible diagnostic results and improves patient survival.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the focus and spirit of the invention. From the above viewpoint, the present invention covers the modifications and alterations of the present invention within the scope of the claims described below and the scope equivalent thereto.

[0023]

[Brief description of drawings]

The drawings attached herewith are for a better understanding of the invention and form and are part of the specification. These drawings illustrate aspects of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a flow diagram showing a conventional method for evaluating changes in heart rate.

FIG. 2 is a flow diagram showing an evaluation method of heart rate change according to the present invention.

FIG. 3 shows a phonocardiogram and the corresponding beating intervals when a subject is examined for 5 minutes according to the method of the present invention. In the figure, the heartbeat peak automatically identified by the computer is shown by a dotted line.

FIG. 4 shows a phonocardiogram and the corresponding beating intervals when a subject is examined for 5 minutes according to the method of the present invention. In the figure, the heartbeat peak automatically identified by the computer is shown by a dotted line.

5 is an HR based on the analysis of the information shown in FIG.
It is a figure which shows the various frequency domain parameters used as the characteristic of V.

FIG. 6 is a diagram showing the correlation between various frequency domain parameters characteristic of HRV obtained by the method of the present invention and by the conventional method for 10 control individuals. .

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Claims (3)

[Claims] 1. A hearing device for collecting a heart sound signal and converting a high frequency sound wave and a low frequency vibration of the heart sound signal into an electric signal, and a frequency domain parameter relating to the electric signal by analyzing the electric signal of the heart sound signal. And a computer system for characterizing changes in heart rate, a heart rate change (HRV) measuring device. 2. A heart sound signal resulting from the contraction of the heart is collected, the collected heart sound signal is digitized, a beat interval is calculated based on the digitized heart sound signal, and the beat interval is converted into a frequency spectrum, And a method for monitoring an autonomic nervous system, which comprises measuring a frequency distribution component relating to a change in heart rate. 3. The step of calculating a beating interval based on the digitized heart sound signal comprises measuring amplitudes and durations of all spikes of the digitized heart sound signal spectrum waveform. , A step of calculating an average value and a standard deviation value of the measured amplitude and duration and using them as a reference of the frequency spectrum waveform, comparing the amplitude and duration of each spike of the digitized heart sound signal with the reference value The autonomic nerve monitoring method according to claim 2, further comprising the steps of: and, when the amplitude and the duration of the compared spikes exceed three times the reference value, the spikes are excluded.