RU2436502C2 - Method for eliminating drift of isoelectric line of electrocardiosignal, and device for its implementation - Google Patents

Abstract

FIELD: measurement equipment. ^ SUBSTANCE: group of inventions refers to medicine. The method consists in extraction in each cycle of heart beats on TP-segment of electrocardiosignal (ECS) counts. Amplitude of each ECS count extracted on TP-segment is recorded till the beginning of the next count. The obtained signal is supplied to low-pass filter inlet. Signal at low-pass filter outlet is subtracted from reference signal of ECS mixture with normal-mode interference, which is pre-delayed for the period of delay of low-pass filter. Device includes extraction unit of ECS counts on TP-segment, filter, delay unit and subtracting unit the outlet of which is the device outlet. Count amplitude recording unit is introduced. Inlet of extraction unit of ECS counts on TP-segment is connected to delay unit inlet, thus forming the device inlet. Outlet of extraction unit of ECS counts on TP-segment is connected to inlet of counts amplitude recording unit the outlet of which is connected to inlet of low-pass filter. Low-pass filter outlet is connected to the first inlet of subtracting unit the second inlet of which is connected to delay unit outlet. Subtracting unit outlet is the device outlet. ^ EFFECT: use of these inventions allows eliminating the drift of isoelectric ECS line without distorting the components of the signal itself, which provides more reliable transfer of ECS shape and contributes to more qualitative ECS analysis. ^ 2 cl, 4 dwg

Description

The invention relates to medicine, in particular to electrocardiography, and can be used in the processing of electrocardiograms.

The isoelectric line drift is caused by the action of additive low-frequency interference on the cardio signal (EX) (polarization of the electrodes, the influence of respiratory waves, the transition process when the contact of the electrode with the body disappears and then restores it, etc.).

Currently, the most common methods for eliminating the contour drift, based on filtering and interpolation.

In the first case, the low-frequency additive interference is eliminated using a high-pass filter [1].

The disadvantage of this method is that along with the drift of the contour from the mixture of EX and interference, a part of the spectral components of the electrocardiogram signal is removed. The suppression of the components in the low-frequency part of the EX spectrum leads, in turn, to the distortion of the shape of the EX at the output of the high-pass filter, which can affect the results of the analysis of the EX.

A possible way to eliminate the drift of the isoelectric line of the electrocardiogram is that reference points on the PQ segment are allocated on the electrocardiogram in each heartbeat cycle and approximating polynomials are drawn through them. The received signal is subtracted from the original signal. The most common at present is the spline approximation [2].

The disadvantage of this method is that the approximation error is methodological. In addition, the PQ segment, which is clearly expressed and lying on the isoline, is not always present in the electrocardiogram, which makes it difficult to select reference points.

Closest to the proposed method (prototype) is a method for eliminating the drift of the isoline [3], which consists in the fact that on the electrocardio signal in each heartbeat cycle, ECS samples are allocated on the TP segment, pulse signals of a complex shape (ISSF) are formed on their basis and they are carried out filtering the latter with a low pass filter.

The disadvantage of this method is the need for additional amplification of the selected signal drift contour, since the signal at the output of the low-pass filter is attenuated by T / τ times. The use of ISSCF cannot fully compensate for the attenuation of the initial signal at the output of the low-pass filter due to the limited duration of the TP segment [4]. With an additional amplification of the signal of the drift of the contour, the high-frequency noise inherent in the amplifier is amplified. This worsens the conditions for further processing of EX.

The essence of the proposed method is as follows.

On the electrocardiogram in each heartbeat cycle, ECS samples are allocated on the TP segment and the amplitude of each of them is stored until the beginning of the next reference. Next, the received signal is fed to the input of a low-pass filter. The signal from the output of the low-pass filter is subtracted from the initial signal of the ECM mixture with additive noise, which is previously delayed by the delay time of the low-pass filter.

The proposed method allows to eliminate the disadvantages of the known method, namely to obtain a drift signal of the contour with an amplitude almost equal to the amplitude of the original continuous signal without additional amplification.

Let us explain the principle of achieving a technical result by performing the above actions with an electrocardiogram.

In figure 1, a shows "clean", i.e. interference-free electrocardiogram.

The TP segment of the electrocardiogram corresponds to the electrical diastole of the heart and, in the absence of interference, lies on the zero line. The difference between the signal on the TP segment from the zero line is due to the action of additive interference (Fig. 1, b). Selecting the ECS samples on the TP segment, we form a sequence of rectangular pulses, which in this case are discrete samples of the isoline drift signal (Fig. 1, c). The signal amplitude at the filter output is weakened by T / τ times, where τ is the duration of the selected sample, T is the pulse repetition period. The amplitude of the selected sample is stored until the start of the next sample, obtaining a sequence of pulses with a duration approximately equal to the pulse repetition period (Fig. 1, d). Filtering the received signal with a low-pass filter allows you to get the restored signal drift of the contour with an amplitude almost equal to the amplitude of the original continuous signal without additional amplification.

When filtering a signal, it delays, so the original signal must also be delayed by a time equal to the delay time of the filter. Subtraction of the selected isoline drift signal from the initial delayed mixture of the ECS and the interference signal allows the latter to be eliminated by freeing the cardiac signal from its effect.

Figure 3 shows the structural diagram of a device for implementing the proposed method for eliminating the drift of the contour, and figure 1 and 2 are diagrams explaining the operation of the device.

To achieve a technical result, which consists in eliminating the drift of the isoelectric line of an electrocardiogram signal, a device for storing the amplitude is stored in a device containing an extraction unit for extracting ECS samples on a TP segment, the input of which is the input of the device, a filter, a delay unit and a subtracting unit, the output of which is the output of the device counts. The input of the ECS sample allocation unit on the TP segment is connected to the input of the delay unit, forming the input of the device, the output of the ECS sample allocation unit on the TP segment is connected to the input of the sample amplitude memory unit, the output of which is connected to the low-pass filter input. The output of the low-pass filter is connected to the first input of the subtracting unit, the second input of which is connected to the output of the delay unit, the output of the subtracting unit is the output of the device.

A device for implementing the proposed method for eliminating drift of an isoelectric line of an electrocardiogram contains a block for extracting 1 ECS samples on the TP segment, a delay unit 2 for the original signal, which is an additive mixture of ECS and interference, a memory unit 3 for the amplitude of the samples, a low-pass filter 4, a subtracting unit 5.

The input of the allocation unit of 1 samples of the EX-samples on the TP segment is connected to the input of the delay unit 2, forming the input of the device, the output of the allocation unit of 1 samples of the EX-samples on the TP segment is connected to the input of the memory unit 3 of the amplitude of the samples, the output of which is connected to the input of the low-pass filter 4, the output of the low-pass filter is connected to the first input of the subtracting unit 5, the second input of which is connected to the output of the delay unit 2, the output of the subtracting unit 5 is the output of the device.

The device operates as follows. The original signal (a mixture of EX and additive interference, Fig. 1, b) is input to the extraction unit 1 of the EX samples in the TP segment and to the input of the delay unit 2. The input signal to this device is an additive mixture of the EX and the interference signal (Fig. 1, b) The output signal is a sequence of rectangular pulses, which are discrete samples of the signal drift of the contour (Fig.1, c). This sequence is fed to the input of the memory block 3 amplitude samples. The output signal of the memory unit 3 is a sequence of rectangular pulses, the duration of which is approximately equal to the period of the pulses (Fig. 1, d), and the amplitude is the amplitude of the corresponding reference. The spectrum of this signal is shown in FIG. 4 (solid vertical lines). The spectrum of this sequence contains components that determine the initial continuous signal of the drift of the isoline, which can be distinguished using a low-pass filter, the amplitude-frequency characteristic of which is shown in Fig. 4 by a dashed line. Thus, when passing the signal generated at the output of the memory unit 3 through the low-pass filter, only the isoline drift signal will be allocated at the filter output. The selected signal of the isoline drift (Fig.2, b) is fed to one of the inputs of the subtracting unit 5. The second input of the subtracting unit 5 receives a signal from the output of the delay unit 2, which is the initial signal delayed by the delay of the low-pass filter from the mixture of the isoline drift and EX. The output of the subtraction unit 5 there is an electrocardiogram (figure 2, c), freed from the influence of additive interference (drift of the contour).

The technical and economic effect of the proposed method and device for its implementation is that the drift of the isoelectric line of the cardiac signal is eliminated without additional amplification. This allows you to get a greater signal to noise ratio, which improves the conditions for further processing of the EX.

Decoding of the notation to figure 3:

1 - block allocation of samples of the EX on the TP segment;

2 - delay unit;

3 - block storing the amplitude of the samples;

4 - low pass filter;

5 - subtracting block.

Literature

1. Kravchenko V.F., Popov A.Yu. Discretization and digital filtering of the electrocardiogram. // Foreign radio electronics. 1996. No1. S.38-44.

2. Cardiomonitors. Equipment for continuous monitoring of the ECG / A.L. Baranovsky, A.N. Kalinichenko, L.A. Manilo et al.: Ed. A.L. Baranovsky and A.P. Nemirko. M .: Radio and communications, 1993.248 s. (S.195-200).

3. RF patent №2251968, АВВ 5/0402. The way to eliminate the drift of the isoline of the electrocardiogram and a device for its implementation / Mikheev A.A., Nechaev G.I.// Discovery. Inventions 2005. No. 14.

4. Melnik OV, Mikheev A.A., Nechaev G.I. Highlighting the drift of the contour of the electrocardiogram. // Biomedical technologies and radio electronics. 2005. No. 1-2. S.26-30.

Claims (2)

1. The way to eliminate the drift of the isoelectric line of the electrocardiogram, which consists in the fact that on the electrocardiogram (EX) in each heartbeat cycle, ECS readings are allocated on the TR segment, characterized in that the amplitude of each ECS readout allocated on the TR segment is remembered before the start of the next readout , then the received signal is fed to the input of the low-pass filter, the signal from the output of the low-pass filter is subtracted from the initial signal of the ECM mixture with additive noise, which is previously delayed by the delay time f low frequency filter. 2. A device for implementing a method of eliminating the drift of an isoelectric line of an electrocardiogram, comprising an ECS sample extraction unit on the TR segment, a filter, a delay unit and a subtracting unit, the output of which is the output of the device, characterized in that a unit for storing the amplitude of the samples is inserted into it, while the input of the ECS samples allocation block on the TR segment is connected to the input of the delay unit, forming the input of the device, the output of the ECS samples allocation block on the TR segment is connected to the input of the sample amplitude storage unit otorrhea connected to the input of a lowpass filter, a lowpass filter output is connected to the first input of the subtractor unit, the second input of which is connected to the output of the delay block, the output of the subtractor unit is an output device.

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