EA039701B1 - Method for adaptive filtering of electrocardiosignal - Google Patents

Abstract

The invention relates to medicine, in particular to cardiology, and can be used for adaptive interference suppression in an electrocardiosignal (ECS). Development of methods and algorithms for filtering the ECS, providing significant interference suppression with minimal distortion of the shape of the useful signal is carried out by expanding the functionality of a method for adaptive filtering of electrocardiosignal, adding additional functions: decomposition of the ECS on harmonics by means of Fourier transformation in the range of from 100 mHz to 1 Hz at a pitch of 100 mHz, from 1 to 10 Hz at a pitch of 1 Hz, from 10 to 100 Hz at a pitch of 10 Hz and from 100 Hz to 1 kHz at a pitch of 100 Hz, measurement of instantaneous values of the bioimpedance Zx(t) by direct measurement of electric dipole parameters on alternating current in the frequency range of from 100 mHz to 1 Hz at a pitch of 100 mHz, from 1 to 10 Hz at a pitch of 1 Hz, from 10 to 100 Hz at a pitch of 10 Hz and from 100 Hz to 1 kHz at a pitch of 100 Hz, measurement of the bioimpedance reference value Z0 by direct measurement of the AC impedance in the range of from 100 mHz to 1 Hz at a pitch of 100 mHz, from 1 to 10 Hz at a pitch of 1 Hz, from 10 to 100 Hz at a pitch of 10 Hz and from 100 Hz to 1 kHz at a pitch of 100 Hz in stationary conditions, namely in conditions of absence of electrical and mechanical interferences, determination of bias of instantaneous values of bioimpedance Zbias(t) by the formula Zbias(t)=Zx(t)-Z0, calculation of the equalization coefficient K for each harmonic determined in the range of from 100 mHz to 1 Hz at a pitch of 100 mHz, from 1 to 10 Hz at a pitch of 1 Hz, from 10 to 100 Hz at a pitch of 10 Hz and from 100 Hz to 1 kHz at a pitch of 100 Hz by the formula equalization of the ECS by multiplying each harmonic by the corresponding equalization coefficient. Electrocardiosignal adaptive filtering makes it possible to minimize the effect of random error component arising from changing the conductivity of tissues of a patient at the moment of registration in conditions of free locomotor activity.

Description

equalization of the EKS by multiplying each harmonic by the equalization coefficient corresponding to it. Adaptive filtering of the electrocardiosignal allows minimizing the influence of the random component of the error that occurs when the conductivity of the patient's tissues changes at the time of registration in conditions of free motor activity.

The invention relates to medicine, in particular to cardiology, and can be used for adaptive interference suppression in an electrocardiosignal (ECS).

Currently, methods of outpatient monitoring of the patient's pacemaker, which provide registration, storage and processing of the pacemaker in conditions of free motor activity (SMA) of the patient, have gained great popularity. Early implementations of these methods in second-generation Holter heart monitoring devices led to problems with high recorded pacemaker noise. Without a direct determination of the nature of interference in the recorded signal, it is customary to speak of their random nature, which does not allow the effective use of traditional methods of filtering digital signals.

If, as a result of interference suppression, distortions of the form of the informative sections of the ECS occur, this can lead to erroneous or inaccurate diagnostic conclusions. In this regard, it is relevant to develop methods and algorithms for filtering the ECS, which provide significant interference suppression with minimal distortion of the useful signal shape [Drozdov D.V. Effect of filtration on the diagnostic properties of biosignals. / Functional diagnostics. 2011, No. 3. S. 75-78]. Thus, the better the filter eliminates interference and the less it distorts the useful signal, the more effective it will be.

A known method of suppressing additive interference [Rangaiyan P.M. Analysis of biomedical signals. // M.: Fizmatlit, 2007. S. 109-111], which consists in the fact that the ECS is filtered with a linear low-pass filter (LPF).

The disadvantage of this method is that together with the additive interference from the mixture of EKS and interference is removed part of the spectral components of the useful signal. In this case, the sharp teeth Q, R, S and other high-frequency components of the useful signal are smoothed out. When the bandwidth of the LPF is expanded, the frequency spectrum of some of the interference will be in the filter's bandwidth and, accordingly, such interference will not be eliminated.

Another well-known analogue of reducing the influence of the additive component of interference is a method of suppressing the influence of additive interference on the electrocardiogram [RF patent 2428107 C1, publ. 11/20/2015. Bull. No. 32, IPC A61B 5/0402], which consists in the fact that in each cardiocycle from an additive mixture of an electrocardiosignal and interference, a section corresponding to the TR segment of the electrocardiosignal is selected, interference is isolated in this section of the electrocardiosignal and the formation of an electrocardiosignal without interference.

The disadvantage of the known method of suppressing the influence of additive noise on the electrocardiogram is that it allows you to eliminate only the fundamental harmonic of the pickup of the power supply.

To describe the nonlinear dependencies of the effect of tissue bioimpedance on current conductivity, numerous equivalent circuits are proposed that allow measurements of impedance on physical models [Belik D.V. Impedance electrosurgery - Novosibirsk: Nauka, 2000. - 237 p.]. In the proposed schemes R ₁ , R ₂ - active resistance of the measuring electrodes; Rp, C _p - reactive components of the impedance; Ri is the resistance of the cytoplasm; Rm is the resistance of the intercellular fluid.

Differences in the impedance of different tissues in the same organism or in organisms of different species are associated with tissue and cellular structural and functional features. Even if the frequency dependence is close in nature, the absolute values of the polarization resistance _Rp and polarization capacitance _Cp , as will be shown later in this work, can differ by an order of magnitude for different tissues. Larger volume and density of cellular elements correspond to higher impedance values.

On the contrary, an increase in the amount of interstitial fluid, blood supply, etc. reduce tissue impedance.

The shape, size of cells, their electrolyte and biochemical composition are also important [Zhchukov A.V. On the study of the electrical conductivity of biological systems. // Successes of modern biology. 1982. - T. 94. - Issue. 3(6). - S. 404-420; Ibragimov R.Sh. On the ratio of capacitive and resistive properties of biological tissues and liquids. // Bull. SO AMS USSR. - 1990. - No. 2. - S. 84-88]. But the main feature of dense cellular tissues is the presence of semi-permeable cellular and intracellular membranes that create an obstacle to the free flow of current.

It is known that changes in tissue conductivity affect the shape of the pacemaker [link]. If we consider the patient's skin as an active load (resistance), then the error generated by the influence of the skin will have the form of a linear additive error. However, it is known that the skin has not only an active, but also a reactive component. From this it follows that the minimization of the linear additive error without taking into account the change in the conductivity of the skin (bioimpedance of tissues) at the time of registration of the pacemaker can lead to undesirable smoothing of sharp Q, R, S waves and other high-frequency components of the useful signal.

Closest to the proposed method (prototype) is a method of adaptive filtering electrocardiosignal [RF patent №2568817, publ. 09/10/2011. Bull. No. 25, IPC A61V 5/04, A61V 5/0402], which consists in the fact that in each cardiocycle from an additive mixture of registered electrocardiosignal and interference, sections corresponding to the TR segment and

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PQRST-complex of the electrocardiosignal, determining the type of interference for each section, selecting the appropriate filter and filtering the selected sections of the electrocardiosignal in accordance with the type of selected interference.

The disadvantage of this method is the fact that the non-linear effect of interference on the ECS is taken into account by dividing the cardiocycle into low-frequency (TP-segment) and high-frequency (PQRST-complex) components, followed by individual filtering of each component separately, which does not allow to fully reduce the effect of nonlinear errors caused, for example, by a change in the bioimpedance of the patient's tissues in the conditions of free motor activity (SMA) of the patient at the time of registration of the pacemaker.

As follows from the analysis of the description of the prototype, adaptive filtering of the pacemaker, the effect of changes in tissue conductivity at the time of registration of the pacemaker is taken into account as a random component, the minimization of which is carried out by one of the proposed known filters that are not designed to effectively reduce the random component of the error.

The invention is aimed at expanding the functionality of the method for adaptive filtering of an electrocardiosignal.

Adaptive filtering of the electrocardiosignal allows minimizing the influence of the random component of the error that occurs when the conductivity of the patient's tissues changes at the time of registration in conditions of free motor activity.

The technical result is achieved by selecting sections corresponding to the TR-segment and PQRST-complex of the electrocardiosignal, determining the type of interference for each section, selecting the appropriate filter and filtering the selected sections of the electrocardiosignal in accordance with the type of selected interference, characterized in that the ECS is additionally decomposed into harmonics with Fourier transform from 100 MHz to 1 Hz in 100 MHz steps, 1 to 10 Hz in 1 Hz steps, 10 to 100 Hz in 10 Hz steps, and 100 Hz to 1 kHz in 100 Hz steps, measurement of instantaneous values bioimpedance Zx(t) by direct measurement of the electrical parameters of two-terminal alternating current in the frequency range from 100 mHz to 1 Hz in steps of 100 mHz, from 1 to 10 Hz in steps of 1 Hz, from 10 to 100 Hz in steps of 10 Hz and from 100 Hz to 1 kHz in 100 Hz steps, bioimpedance reference Z ₀ measurement by direct AC impedance measurement from 100 mHz to 1 Hz in 100 mHz steps, 1 to 10 Hz in steps 1 Hz, from 10 to 100 Hz in steps of 10 Hz and from 100 Hz to 1 kHz in steps of 100 Hz in stationary conditions, namely in the absence of electrical and mechanical interference, determining the offset of instantaneous bioimpedance values Z _shift (t) using the formula ^ offset CO ^{= ζ} χ^ calculation of the equalization factor K for each harmonic defined in the range from 100 MHz to 1 Hz in 100 MHz steps, from 1 to 10 Hz in 1 Hz steps, from 10 to 100 Hz in 10 Hz steps and from 100 Hz up to 1 _kHz with a _step of _{100 Hz} according to the formula -------I=----------------------,

Zq y y ζ ₀ ζ _ϋ equalization of the EKS by multiplying each harmonic by the equalization coefficient corresponding to it.

The method is illustrated by the figures.

In FIG. 1 shows a diagram of the proposed method for adaptive filtering of the electrocardiosignal.

In FIG. 2 shows an extended scheme of additional steps of the method for adaptive filtering of the electrocardiosignal.

In FIG. 3 shows a measuring circuit for indirect measurement of bioimpedance on alternating current.

In FIG. 4 is a graphical representation illustrating the change in skin bioimpedance over time.

In FIG. Figure 5 shows a graphic image illustrating the effect of changes in the bioimpedance of the skin on the amplitudes of informative sections (P-wave, QRS complex and ST-segment) of the ECS cardiocycle.

The method of adaptive filtering EX is as follows. EKS registration is the process of measuring potentials on the patient's torso. These potentials characterize the electrical activity in various parts of the heart and make it possible to determine conduction disturbances in certain parts of the heart (endocardium, myocardium, etc.). In the stationary conditions of registration of the EKS, the patient is either completely motionless or with minimal body movement (thoracic contraction during breathing) during the recording process. Since there is no physical activity and the body is motionless, the bioimpedance of the skin does not change significantly. In each cardiocycle, from the additive mixture of the registered electrocardiosignal and interference, sections corresponding to the TP-segment and PQRST-complex of the electrocardiosignal are selected, the type of interference for each section is determined, the corresponding filter is selected, and the selected sections of the electrocardiosignal are filtered in accordance with the type of selected interference, characterized in that additionally, the ECS is decomposed into harmonics using the Fourier transform in the range from 100 MHz to 1 Hz in 100 MHz steps, from 1 to 10 Hz in 1 Hz steps, from 10 to 100 Hz in 10 Hz steps and from 100 Hz to 1 kHz with step

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100 Hz, measurement of instantaneous values of bioimpedance Z _x (t) by direct measurement of the electrical parameters of two-terminal networks on alternating current in the frequency range from 100 mHz to 1 Hz in steps of 100 mHz, from 1 to 10 Hz in steps of 1 Hz, from 10 to 100 Hz in steps of 10 Hz and from 100 Hz to 1 kHz in steps of 100 Hz, measurement of the bioimpedance reference value Z ₀ by direct measurement of the impedance on AC in the range from 100 mHz to 1 Hz in steps of 100 mHz, from 1 to 10 Hz in steps of 1 Hz, from 10 to 100 Hz in steps of 10 Hz and from 100 Hz to 1 kHz in steps of 100 Hz in stationary conditions, namely in the absence of electrical and mechanical interference, determining the offset of instantaneous bioimpedance values _Zshift (t) using the formula ^shift (0 “ Zq, calculation of the equalization factor K for each harmonic, defined in the range from 100 MHz to 1 Hz in 100 MHz steps, from 1 to 10 Hz in 1 Hz steps, from 10 to 100 Hz in 10 Hz steps, and from 100 Hz up to 1 kHz with a step of 100 Hz according to the formula „ E / (z ₀ ± Z _CMeU j (t)) \ (^ o ± ^ shift C)) (Z ₀ ± (ZZ ₀ )) to ~ - I- ----------I=-----------=----------,

Zq y E y Zq Zq equalization of the ECS by multiplying each harmonic by the equalization coefficient corresponding to it.

Thus, the change in bioimpedance with time AZ _x (t) under stationary conditions is negligibly small:

AZ _x (t) = Z _x (t)-Z _o -+O (1)

It follows from this that = (2)

In contrast to inpatient conditions, in outpatient conditions for registration of the pacemaker, the patient's motor activity is not limited in any way, secretion (sweat secretions) is possible, which causes a change in the skin's own bioimpedance and, as shown in Fig. 4, negatively affects the form of the registered EX.

From this it follows that the change in the bioimpedance of the skin is described by the following formula:

(3)

Since Z _x (t) ^ Z ₀ , then the influence exerted by a parasitic change in skin bioimpedance over time will have the following form:

(4) ιΛίω^ where ^υ χ is a parasitic voltage caused by AZ _x (t) in the outpatient setting of EKS registration.

Consider the implementation of the proposed method for adaptive filtering of the electrocardiogram (see Fig. 2).

Taking into account the change in the conductivity of the skin over time will make it possible to transfer the interference, the main component of which is a parasitic voltage drop caused by a change in tissue bioimpedance, from the category of random to the category of systematic. This will allow more efficient use of known filters of the prototype, designed to work with systematic noise.

Stage measurement of bioimpedance. At the frequency of the i-th harmonic, which is in the range from 100 MHz to 1 Hz in steps of 100 MHz, from 1 to 10 Hz in steps of 1 Hz, from 10 to 100 Hz in steps of 10 Hz and from 100 Hz to 1 kHz in steps of 100 Hz, a bioimpedance measurement is performed, which is a measurement of the voltage drop across the reference resistor R ₀ , which is part of the measuring circuit shown in FIG. 3.

The measuring circuit is a sinusoidal voltage generator, which is fed to the measuring circuit formed by the measurement object with the impedance Z and the reference resistor R ₀ forming a voltage divider.

______ ._____ ... .. ... ___________, In the measuring circuit, a current appears ( ^z + "o) where UГ is the generator voltage, Z is the impedance of the measurement object, and R0 is the resistance of the reference resistor. Using an AC voltmeter, the effective value of the voltage across the resistor R0 (UR0) is measured, determined by the formula C - ^fio (Z + Roy

Thus, the bioimpedance of the skin at the frequency of the i-th mode is determined by the following formula:

(u _r -u _RQ ) (5)

Stage calculation of the parameters of the equalization filter. To correct each ECS mode in accordance with the change in the skin bioimpedance, the authors propose to calculate the equalization coefficient for the i-th mode as follows. Let us assume that the heart can be represented as a generator with an EMF equal to E. Then a current will flow on the skin surface equal to the ratio of the generator EMF_ (4oj ” 7 ), torus and bioimpedance of the skin where Z _skin is the impedance of the skin. As mentioned above, in stationary conditions, the impedance Z of the _skin is taken as the reference value of the impedance in stationary conditions Z ₀ . On an outpatient basis, due to changes in skin bioimpedance, the effect is described

- 3 ⁰³⁹⁷⁰¹ earlier reasons, the following is true: the skin bioimpedance value is defined as the value of the reference skin bioimpedance Z ₀ plus or minus the bioimpedance shift from the norm Z _cm e _w (t), defined as the difference between the instantaneous value of the bioimpedance at the frequency of the i-th mode (Z) and the reference impedance value in stationary conditions Zq. Thus, the real current arising on the surface of the ^skin obeys ^the formula

To minimize the effect of Z _cm e _w (t), it is necessary to multiply the right side of formula (6) by the dimensionless coefficient K, which takes into account the change in Z _shift (t) (). Formula ( ₆ ) shows the output of the desired coefficient _K , called _{the equalization coefficient} ' y E ) ” ζ ~ Tq '

EQ stage. This stage includes the multiplication of each ECS mode by the equalization coefficient corresponding to it, followed by signal synthesis using the inverse Fourier transform. The form of the EKS obtained after synthesis will be changed taking into account the influence of the patient's skin bioimpedance changing over time and is suitable for further processing and analysis.

CLAIM

Claims (1)

CLAIM A method for adaptive filtering of an electrocardiosignal (ECS), which consists in the fact that in each cardiocycle, from an additive mixture of registered electrocardiosignal and interference, sections corresponding to the TP-segment and PQRST-complex of the electrocardiosignal are selected, the type of interference for each section is determined, the corresponding filter is selected, and the selected sections of the electrocardiosignal in accordance with the type of isolated interference, characterized in that the ECS is additionally decomposed into harmonics using the Fourier transform in the range from 100 MHz to 1 Hz in 100 MHz steps, from 1 to 10 Hz in 1 Hz steps, from 10 to 100 Hz in 10 Hz steps and from 100 Hz to 1 kHz in 100 Hz steps, measurement of instantaneous values of bioimpedance Z _x (t) by direct measurement of the electrical parameters of two-terminal AC networks in the frequency range from 100 MHz to 1 Hz in 100 MHz steps, from 1 to 10 Hz in 1 Hz steps, 10 to 100 Hz in 10 Hz steps, and 100 Hz to 1 kHz in 100 Hz steps, reference measurement Z0 bioimpedance readings by direct AC impedance measurement from 100 mHz to 1 Hz in 100 mHz steps, from 1 to 10 Hz in 1 Hz steps, from 10 to 100 Hz in 10 Hz steps, and from 100 Hz to 1 kHz with in steps of 100 Hz in stationary conditions, namely in the absence of electrical and mechanical interference, determining the offset of instantaneous bioimpedance values Z _shift (t) using the formula Z _shift (t)=Z _x (t)-Z _Q , calculation of the equalization coefficient K for each harmonics defined in the range from 100 MHz to 1 Hz in 100 MHz steps, from 1 to 10 Hz in 1 Hz steps, from 10 to 100 Hz in 10 Hz steps and from 100 Hz to 1 kHz in 100 Hz steps using the formula