KR101623260B1 - A apparatus for extracting heart sound frequency envelope information and a method thereof - Google Patents

Abstract

The present invention discloses an apparatus and method for extracting heart sound frequency envelope information. The apparatus includes a heart sound measuring unit for receiving a heart sound signal and converting the vibration of the chest wall into an electrical signal and outputting the electrical signal; A sampling unit for receiving the converted electrical signal and sampling the converted electrical signal at a predetermined sampling frequency; And a signal processor for receiving the sampled electrical signal, performing impedance matching and filtering, and extracting an envelope of the cardiac sound signal by adjusting the natural frequency and the attenuation factor. According to the present invention, it is possible to extract the heartbeat frequency envelope curve in which the movement of the maximum frequency and the peak characteristics of the original power spectral density waveform are more accurately reflected. In addition, it is possible to extract more envelope information and more accurate heart sound frequency envelope curve than the method of extracting the envelope of the heart sound signal which is controlled through the adjustment of the conventional AR model coefficient.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for extracting heart sound frequency envelope information,

More particularly, the present invention relates to an apparatus and method for extracting envelope information, and more particularly, to a method and apparatus for extracting envelope information by applying heart sound signals and adjusting a natural frequency and a decay rate using a first- To an apparatus and method for extracting heart sound frequency envelope information capable of extracting envelope curves.

In general, PCG (Phonocardiography) testing is widely used in clinical practice as a primary and basic means of early diagnosis of heart disease.

However, a physician skilled in dealing with a stethoscope needs a long-time listening training of a stethoscope, and a subjective judgment is made when diagnosing a heart disease with a stethoscope, and there is a problem that some heart sounds are not easy to be distinguished by human hearing.

The normal heart sounds consist of S1 and S2, which close the tricuspid plate and the tricuspid, and S1 and S2, respectively. In the case of heart disease, S2 disruption (when the time difference between two meniscus is clear), and heart or systolic or diastolic heart murmurs due to S3 or S4. Therefore, it is important to detect the occurrence of abnormal signals and the location of the murmur in the diagnosis of heart disease.

Meanwhile, existing heart sound analysis methods include energy-based envelope extraction method, envelope extraction method based on sub-band energy, envelope extraction method based on Shannon energy, envelope extraction method based on Hilbert transformation, wavelet based methods, moment based methods, and heart sound model based methods.

However, in the conventional method based on the envelope extraction, it is assumed that S1 and S2 are dominant, and there is a limitation that the noise is determined incorrectly when the energy of the heart murmur is large. The conventional wavelet-based method has a problem in that the low- , The method based on the heart sound model has a limitation in that the performance is degraded due to lack of accuracy of the model.

1 is a block diagram of a signal processing unit in a device for extracting heart sound frequency envelope information according to the related art.

FIG. 2 is a graph showing an experimental result of calculating a heart sound frequency envelope curve using a heart sound frequency envelope information extracting apparatus according to the prior art, wherein (A) is a normal heart sound, (B) is aortic regurgitation heart murmur Experimental results show that the gray part shows the power spectral density (PSD) and the dotted line shows the extracted sound spectrum envelope curve.

The operation of the heart sound frequency envelope information extracting apparatus according to the prior art will be described with reference to FIGS. 1 and 2. FIG.

When the cardiac sound measuring unit 10 receives the heart sound signal and converts the vibration of the chest wall into an electrical signal, the sampling unit 20 receives the converted electrical signal and samples it at a predetermined sampling frequency.

Next, the impedance matching unit 30 receives the sampled electrical signal to match the impedance, and the filter unit 41 receives the impedance-matched electrical signal and band-pass filters the signal of a predetermined frequency band.

When the power spectral density calculation unit 42 receives the band-pass filtered electrical signal and calculates the power spectral density, the envelope extraction unit 43 receives the calculated electrical power spectral density and adjusts the AR model coefficient Extract the envelope of the controlled heart sound signal.

Here, the envelope refers to a curve formed by connecting the maximum values of the electrical signals of the heart sound, and the AR model coefficient is a coefficient of aortic regurgitation. The Akaike information criterion, AIC).

The normalization unit 44 receives the envelope of the extracted heart sound signal and normalizes it, and finally calculates the heart sound frequency envelope curve.

Accordingly, the conventional envelope information extracting apparatus can extract the envelope of the heart sound signal having high sensitivity and specificity.

However, as shown in FIG. 2, the conventional envelope information extracting apparatus is different from the conventional power spectral density waveform in that the maximum frequency fmax is shifted and the peaks of the peak frequency characteristics are sufficiently reflected, There is a problem that a mismatching error occurs.

An object of the present invention is to provide a method and apparatus for detecting heart sounds and heart murmurs separately from heart sound signals and simultaneously detecting the movement of the maximum frequency and the characteristics of each peak by adjusting the natural frequency and the decay rate using a first- And a heart sound frequency envelope information extracting device for extracting a heart sound frequency envelope curve.

Another object of the present invention is to provide an envelope information extracting method of an envelope information extracting apparatus for achieving the above object.

In order to achieve the above object, a heart sound frequency envelope information extracting apparatus according to the present invention includes a heart sound measuring unit for receiving a heart sound signal, converting a vibration of a chest wall into an electrical signal, and outputting the electrical signal; A sampling unit for receiving the converted electrical signal and sampling the converted electrical signal at a predetermined sampling frequency; And a signal processor for receiving the sampled electrical signal, performing impedance matching and filtering, and extracting an envelope of the cardiac sound signal by adjusting the natural frequency and the attenuation factor.

In order to achieve the above object, the signal processing unit of the heart sound frequency envelope information extracting apparatus of the present invention includes: an impedance matching unit for receiving the sampled electrical signal to match the impedance; A filter unit receiving the impedance-matched electrical signal and band-pass filtering the signal of a predetermined frequency band; A power spectral density calculation unit for receiving the filtered electrical signal and calculating a power spectral density; An envelope extracting unit for extracting an envelope of the heart sound signal using the first degree of freedom vibration model by receiving the electric signal in which the power spectral density is calculated; A time delay compensator for receiving an envelope of the extracted heart sound signal and compensating for a time delay due to the natural frequency application; And a normalizer for receiving and normalizing the time delayed compensated heart sound signal.

In order to achieve the above object, the impedance matching unit of the heart sound frequency envelope information extracting apparatus of the present invention is an operational amplifier.

In order to achieve the above object, the filter unit of the heart sound frequency envelope information extracting apparatus of the present invention is a band-pass filter.

In order to achieve the above object, the time delay compensation unit of the heart rate frequency envelope information extracting apparatus of the present invention compensates the time delay using a table calculated in advance.

In order to achieve the above object, the normalizing unit of the heart sound frequency envelope information extracting apparatus of the present invention is characterized by square-root processing and normalizing the time-delay compensated heart sound signal.

In order to achieve the above object, the heart sound frequency envelope information extracting apparatus of the present invention comprises a chest piece for receiving and transmitting the heart sound signal due to the vibration of the chest wall caused by contraction and relaxation of the heart; And a condenser microphone for receiving the heart sound signal and converting the vibration of the chest wall into an electric signal.

The apparatus for extracting heart sound frequency envelope information according to the present invention further includes a stethoscope for receiving and transmitting the heart sound signal.

In order to achieve the above object, the apparatus for extracting heart sound frequency envelope information according to the present invention further comprises a storage unit for storing the sampled electrical signals in real time.

According to another aspect of the present invention, there is provided a heart sound frequency envelope information extracting apparatus, further comprising a heart sound frequency curve evaluating unit for receiving the normalized heart sound signal and evaluating the received normal heart sound signal according to a mean square root error, do.

According to another aspect of the present invention, there is provided a method for extracting heart sound frequency envelope information comprising the steps of: (a) measuring a heart sound to which a heart sound signal is applied and a chest wall vibration is converted into an electrical signal; (b) a sampling unit receiving the converted electrical signal and sampling at a predetermined sampling frequency; And (c) extracting an envelope of the heart sound signal through impedance matching and filtering of the sampled electrical signal, and adjusting the natural frequency and the attenuation factor of the signal processing unit.

According to another aspect of the present invention, in the step (c) of extracting the heart sound frequency envelope information according to the present invention, the impedance matching unit receives the sampled electrical signal and matches the impedance. Band-pass filtering a signal of a predetermined frequency band by receiving an electrical signal whose impedance matches the filter unit; The power spectral density calculation unit receiving the filtered electrical signal and calculating a power spectral density; Extracting an envelope of the cardiac sound signal using a first degree of freedom vibration model by receiving an electrical signal in which an envelope extracting unit calculates the power spectral density; Compensating a time delay due to the natural frequency application by receiving an envelope of the extracted heart sound signal; And normalizing the normalized signal by applying a time-lag compensated heart sound signal.

According to another aspect of the present invention, there is provided a method for extracting heart sound frequency envelope information, comprising the steps of: The storage unit storing the sampled electrical signal in real time; And a heart rate frequency curve evaluating unit receiving the normalized heart sound signal and evaluating the heart rate signal by an average square root error and outputting the evaluated value.

According to the present invention, it is possible to extract the heartbeat frequency envelope curve in which the movement of the maximum frequency and the peak characteristics of the original power spectral density waveform are more accurately reflected.

In addition, it is possible to extract more envelope information and more accurate heart sound frequency envelope curve than the method of extracting the envelope of the heart sound signal which is controlled through the adjustment of the conventional AR model coefficient.

1 is a block diagram of a signal processing unit in a device for extracting heart sound frequency envelope information according to the related art.
FIG. 2 is a graph showing experimental results of calculating a heart sound frequency envelope curve using a heart sound frequency envelope information extracting apparatus according to the prior art.
3 is a block diagram of an apparatus for extracting heart sound frequency envelope information according to the present invention.
FIG. 4 is a block diagram of a signal processing unit 400 in the envelope information extracting apparatus according to the present invention shown in FIG.
5 is a flowchart illustrating an operation of a method for extracting heart sound frequency envelope information according to the present invention.
FIG. 6 is a block diagram for explaining a first degree-of-freedom vibration model used in step S150 in the method for extracting heart sound frequency envelope information according to the present invention shown in FIG.
FIGS. 7A and 7B are graphs showing results of calculation of heart sound frequency envelope curves for analyzing the effect of eigenfrequency on the method for extracting heart sound frequency envelope information according to the present invention.
8A and 8B are graphs showing experimental results of calculating heartbeat frequency envelope curves for analyzing the influence of the decay rate on the method for extracting heart sound frequency envelope information according to the present invention.
FIG. 9 is a graph showing a result of a mean square root error when the natural frequency is changed to 1-100 Hz and the decay rate is changed 10-500% with respect to the method for extracting heart sound frequency envelope information according to the present invention.
FIGS. 10A and 10B are graphs showing experimental results obtained by calculating the heart sound frequency envelope curve using the apparatus for extracting heart sound frequency envelope information according to the present invention, compared with experimental results of calculating heart sound frequency envelope curves through adjustment of the conventional AR model coefficients Graph.

Hereinafter, an apparatus and method for extracting heart sound frequency envelope information according to the present invention will be described with reference to the accompanying drawings.

3 is a block diagram of a heart sound frequency envelope information extracting apparatus according to the present invention. The heart sound frequency envelope information extracting apparatus 100 includes a heart sound measuring unit 100, a stethoscope unit 200, a sampling unit 300, a signal processing unit 400, a storage unit 500, And a frequency curve evaluation unit 600.

Referring to FIG. 3, the function of each component of the heart sound frequency envelope information extracting apparatus according to the present invention will be described as follows.

The heart sound measuring unit 100 receives a heart sound signal generated by vibrations of the chest wall due to sound generated when the heart is contracted and relaxed through the chest piece 110 and transmits the vibration through the condenser microphone 120 as an electrical signal And outputs it.

The stethoscope unit 200 receives and transmits a heart sound signal through the chest piece 110 in the heart sound measurement unit 100.

The sampling unit 300 receives the electrical signal converted through the condenser microphone 120 in the heart sound measuring unit 100, samples the signal at a predetermined sampling frequency, and stores the sampled signal in the user terminal 500 in real time. Here, the predetermined sampling frequency is preferably set to 16 bits 8 kHz.

The signal processing unit 400 receives an electrical signal sampled from the sampling unit to match the impedance, filters the impedance-matched signal, extracts an envelope through adjustment of a natural frequency and a damping factor, Compensates the delay and normalizes it and outputs it.

The heart sound frequency curve evaluating unit 600 receives the normalized heart sound signal and evaluates it by a root mean square error (RMSE) and outputs it.

FIG. 4 is a block diagram of a signal processing unit in the envelope information extracting apparatus according to the present invention shown in FIG. 3 and includes an impedance matching unit 410 and a control unit 420. The control unit 420 includes a filter unit 421, A power spectrum density calculation unit 422, an envelope extraction unit 423, a time delay compensation unit 424, and a normalization unit 425.

3 and 4, the functions of the respective components of the signal processing unit in the apparatus for extracting heart sound frequency envelope information according to the present invention will now be described.

The impedance matching unit 410 is composed of an operational amplifier (OP AMP), receives an electrical signal sampled from the sampling unit, and matches the impedance.

The filter unit 421 is composed of a band-pass filter, and receives an electrical signal whose impedance is matched from the impedance matching unit 410, and band-pass filters the signal of a predetermined frequency band. Here, the predetermined frequency band is preferably set to 5 to 700 Hz.

The power spectral density calculation unit 422 receives a band-pass filtered electrical signal from the filter unit 421 and calculates power spectral density.

The envelope extractor 423 receives an electrical signal from which the power spectral density is calculated from the power spectral density calculator 422, and extracts the envelope of the signal using the first degree of freedom vibration model.

The time delay compensator 424 compensates for the time delay due to the low eigenfrequency application using a precomputed table instead of cross-correlation in software to increase the computation speed.

For convenience of calculation, the normalizing unit 425 receives the time-lag compensated heartbeat signal from the time delay compensating unit 424, performs square-root processing, and normalizes the signal.

5 is a flowchart illustrating an operation of a method for extracting heart sound frequency envelope information according to the present invention.

FIG. 6 is a block diagram for explaining a first degree-of-freedom vibration model used in step S150 in the method for extracting heart sound frequency envelope information according to the present invention shown in FIG.

The operation of the embodiment of the envelope information extracting method using the syringe pump according to the present invention will be described with reference to FIGS. 3 to 6 as follows.

First, a signal that occurs when a chest wall vibrates due to the sound generated when the heart contracts and relaxes is called a cardiac signal.

The cardiac sound measuring unit 100 includes a chestpiece 110 and a condenser microphone 120. The cardiac sound measuring unit 100 receives a heart sound signal through the chest piece 110 and transmits the vibration of the chest wall through the condenser microphone 120 electrically And outputs the converted signal (S110).

The sampling unit 300 receives the converted electrical signal through the condenser microphone 120 in the cardiac sound measuring unit 100 and samples it at a predetermined sampling frequency, for example, 16 bits 8 kHz (S120). The sampled and collected data is stored in the storage unit 500 such as a PC in real time.

The impedance matching unit 410 in the signal processing unit receives the sampled electrical signal from the sampling unit and matches the impedance of the signal.

The filter unit 421 applies an electrical signal whose impedance is matched from the impedance matching unit 410 and band-pass filters the signal of a predetermined frequency band, for example, 5 to 700 Hz (S130). Here, the predetermined frequency band is preferably set to 5 to 700 Hz.

At this time, pre-processing is performed using wavelet transform. In order to remove unnecessary signals from the original signal, a frequency component of 700 Hz or more and a frequency component of 5 Hz or less are removed.

The power spectral density calculation unit 422 receives the band-pass filtered electrical signal from the filter unit 421 and calculates a power spectral density (S140). Here, the term "power spectral density" refers to a distribution of energy per unit frequency obtained through Fourier transform when the analysis section is infinite in the waveform analysis.

That is, in the random processor data x (t) having the autocorrelation function R _x (t), the power spectral density of x (t) is calculated by the Fourier transform of the autocorrelation function R _x (tau) Calculate by conversion.

The envelope extractor 423 receives the electrical signal from which the power spectral density is calculated from the power spectral density calculator 422 and controls it by the natural frequency p and the decay rate z using the first degree of freedom vibration model The envelope of the extracted heart sound signal is extracted (S150).

The primary degree of freedom vibration model is shown in Figure 6 as a first degree of freedom with input S _x (f) and output response S _y (f) in a primary spring-mass-damper system The analytical model is given by the following equation (2).

Where m is the mass, c is the damping coefficient, and k is the spring coefficient.

Assuming that r (f) in FIG. 6 has a value of 0 as the displacement of the rack, Equation (2) can be written as Equation (3).

를 나타내고, ζ는 감쇠율(damping factor)로서

를 나타내며,

를 나타낸다.Here, p is a natural frequency

, And ζ is a damping factor

Lt; / RTI >

.

As shown in Equation (3), the first degree of freedom vibration model used in the step S150 in the method for extracting the heart sound frequency envelope information according to the present invention is based on the two analysis parameters, the natural frequency p and the decay rate? .

That is, since the time lag is generated by applying the low natural frequency in the envelope extraction of the heart sound signal in step S150, the time delay compensation unit 424 compensates A cross-correlation function is used.

Here, CC (f) denotes a cross-correlation function between the input spectrum and the output response.

Alternatively, instead of cross-correlation in software, the time delay compensator 424 may use a pre-computed table to compensate for the time delay due to hardware low natural frequency application (S160).

The normalizing unit 425 receives the time-lag compensated heartbeat signal from the time delay compensating unit 424, performs a square-root processing as shown in Equation (8), and normalizes it (S170).

The cardiac frequency curve evaluating unit 600 receives the normalized heartbeat signal from the normalizing unit 425 and evaluates it according to RMSE as shown in Equation (9), and outputs it (S180).

Here, the mean square error is a measure commonly used when dealing with the difference between the estimated value or the value predicted by the model and the observed value in the actual environment, where the input S _x (f) is the input heart sound signal and P (f) Means a normalized heart sound signal.

In this embodiment, a value of an appropriate natural frequency is selected as a value when the differential value of Equation (9) is smaller than 0.3, and a proper attenuation rate is obtained when all the spectra have positive values and the differential value of Equation (9) Of the total.

7A and 7B are graphs showing results of calculation of a heart rate frequency envelope curve for analyzing the influence of a natural frequency on a method for extracting heart sound frequency envelope information according to the present invention. The aortic regurgitation is the experimental result of the murmur, the gray part is the PSD, and the red curve is the extracted heart sound frequency envelope curve.

8A and 8B are graphs showing results of calculation of a heart rate frequency envelope curve for analyzing the influence of a decay rate on a method for extracting heart sound frequency envelope information according to the present invention. (aortic regurgitation) is the experimental result of the murmur, the gray part is the PSD, and the red curve is the extracted heart sound frequency envelope curve.

9 is a graph showing a result of the mean square root error when the natural frequency is changed to 1-100 Hz and the decay rate is changed 10-500% with respect to the method for extracting heart sound frequency envelope information according to the present invention, , And the dotted line represents the experimental result of the aortic regurgitation murmur.

FIGS. 10A and 10B are graphs showing experimental results obtained by calculating the heart sound frequency envelope curve using the apparatus for extracting heart sound frequency envelope information according to the present invention, and comparing the experimental results obtained by calculating the heart sound frequency envelope curve by adjusting the conventional AR model coefficient 10A and 10B are experimental results of the aortic regurgitation murmur, the gray part is the power spectral density, the dotted line is the heart sound frequency envelope curve extracted by the conventional AR model coefficient control, The curve represents the heart sound frequency envelope curve extracted according to the present invention.

7A and 7B, when the decay rate ζ is defined as 70.7% and the natural frequency is changed from 1 Hz to 100 Hz, the aortic regurgitation heart murmur has a higher maximum frequency fmax than the normal heart sound It has been found that the frequency components are high in the 200 to 500 Hz band, which is presumably due to the presence of diastolic murmur.

8A and 8B, when the natural frequency is defined as 35 Hz and the decay rate (ζ) is changed from 10% to 500%, as in FIGS. 7A and 7B, the aortic regurgitation heart murmur is normal It has been found that it has a higher maximum frequency (fmax) than the heart sound and a higher frequency component in the band of 200 to 500 Hz.

Also, as shown in FIG. 9, it can be seen that the mean square error value has a larger mean square error value in the case of the aortic regurgitation heart murmur than in the case of the normal heart sound as the natural frequency or the decay rate (?) Increases.

As shown in FIGS. 10A and 10B, the envelope information extracting apparatus according to the present invention, when compared with the experimental result of calculating the conventional heart sound frequency envelope curve shown in FIG. 2, (fmax) and the heart sound frequency envelope curve in which each peak characteristic is more accurately reflected.

Through this, it is possible to extract more envelope information and more accurate heart sound frequency envelope curve than the method of extracting the envelope of the heart sound signal which is controlled through the adjustment of the conventional AR model coefficient.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. It will be understood that the present invention can be changed.

100: heart sound measuring unit
200: Stethoscope department
300: Sampling unit
400: Signal processor
410: Impedance matching unit
420:
421:
422: power spectral density calculation unit
423: envelope extracting unit
424: Time delay compensator
425: normalization unit
500:
600: heart sound frequency curve evaluation unit

Claims (13)

A heart sound measuring unit for receiving the heart sound signal and converting the vibration of the chest wall into an electrical signal and outputting the electrical signal;
A sampling unit for receiving the converted electrical signal and sampling the converted electrical signal at a predetermined sampling frequency; And
A signal processor for receiving the sampled electrical signal, performing impedance matching and filtering, and extracting an envelope of the cardiac sound signal by adjusting a natural frequency and a decay rate; And,
The signal processing unit
An impedance matching unit for receiving the sampled electrical signal and matching the impedance;
A filter unit receiving the impedance-matched electrical signal and band-pass filtering the signal of a predetermined frequency band;
A power spectral density calculation unit for receiving the filtered electrical signal and calculating a power spectral density;
An envelope extracting unit for extracting an envelope of the heart sound signal using the first degree of freedom vibration model by receiving the electric signal in which the power spectral density is calculated;
A time delay compensator for receiving an envelope of the extracted heart sound signal and compensating for a time delay due to the natural frequency application; And
A normalizer for receiving and normalizing the time delayed compensated heart sound signal;
And a control unit
Heart sound frequency envelope information extraction device.
delete The method according to claim 1,
The impedance matching unit
An amplifier,
Heart sound frequency envelope information extraction device.
The method according to claim 1,
The filter unit
Band pass filter.
Heart sound frequency envelope information extraction device.
The method according to claim 1,
The time delay compensation unit
And the time delay is compensated using a pre-calculated table.
Heart sound frequency envelope information extraction device.
The method according to claim 1,
The normalization unit
Characterized in that said time delay compensated cardiac signal is squared-root processed to normalize.
Heart sound frequency envelope information extraction device.
The method according to claim 1,
The heart sound measuring unit
A chest piece for receiving and transmitting the heart sound signal due to vibration of the chest wall caused by contraction and relaxation of the heart; And
A condenser microphone for receiving the heart sound signal and converting the vibration of the chest wall into an electrical signal;
And a control unit
Heart sound frequency envelope information extraction device.
The method according to claim 1,
The envelope information extracting apparatus
A stethoscope for receiving and transmitting the heart sound signal;
Further comprising:
Heart sound frequency envelope information extraction device.
The method according to claim 1,
The envelope information extracting apparatus
A storage unit for storing the sampled electrical signals in real time;
Further comprising:
Heart sound frequency envelope information extraction device.
The method according to claim 1,
The envelope information extracting apparatus
A heart sound frequency curve evaluator for receiving the normalized heart sound signal and evaluating and outputting the normal heart sound signal according to an average square root error;
Further comprising:
Heart sound frequency envelope information extraction device.
(a) measuring a heart sound to which a heart sound measuring unit receives a heart sound signal and converts the vibration of the chest wall into an electrical signal and outputs the electrical sound;
(b) a sampling unit receiving the converted electrical signal and sampling at a predetermined sampling frequency; And
(c) extracting an envelope of the heart sound signal through impedance matching and filtering of the sampled electrical signal, and adjusting the natural frequency and the attenuation factor; / RTI >
The step (c)
The impedance matching unit receiving the sampled electrical signal to match the impedance;
Band-pass filtering a signal of a predetermined frequency band by receiving an electrical signal whose impedance matches the filter unit;
The power spectral density calculation unit receiving the filtered electrical signal and calculating a power spectral density;
Extracting an envelope of the cardiac sound signal using a first degree of freedom vibration model by receiving an electrical signal in which an envelope extracting unit calculates the power spectral density;
Compensating a time delay due to the natural frequency application by receiving an envelope of the extracted heart sound signal; And
Wherein the normalization unit receives and normalizes the time-lag compensated heart sound signal; ≪ / RTI >
Extraction method of heart sound frequency envelope information.
delete 12. The method of claim 11,
The envelope information extraction method
Transmitting a heart sound signal to the stethoscope;
The storage unit storing the sampled electrical signal in real time; And
Evaluating and outputting the normalized heart sound signal according to a mean square root error;
Lt; RTI ID = 0.0 > 1, < / RTI &
Extraction method of heart sound frequency envelope information.

Images