Chavdar Levkov

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Subtraction Method for Powerline Interference Removing from Ecg

This paper presents the subtraction method for interference cancellation in ECG. In contrast to t... more This paper presents the subtraction method for interference cancellation in ECG. In contrast to the well-known hardware and software filters, the method does not affect the signal frequency components around the rated powerline frequency. The method searches for linear segments in the ECG signal. Then a digital filter is used to remove the interference from these segments. The samples of the interference signal are computed in these segments and later on these samples are used to remove by subtraction the interference from the signal where non-linear segments are encountered. A theoretical generalised approach of the method is developed in the paper.

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Removal of power-line interference from the ECG: a review of the subtraction procedure

Biomedical Engineering Online, Aug 23, 2005

Background: Modern biomedical amplifiers have a very high common mode rejection ratio. Neverthele... more Background: Modern biomedical amplifiers have a very high common mode rejection ratio. Nevertheless, recordings are often contaminated by residual power-line interference. Traditional analogue and digital filters are known to suppress ECG components near to the power-line frequency. Different types of digital notch filters are widely used despite their inherent contradiction: tolerable signal distortion needs a narrow frequency band, which leads to ineffective filtering in cases of larger frequency deviation of the interference. Adaptive filtering introduces unacceptable transient response time, especially after steep and large QRS complexes. Other available techniques such as Fourier transform do not work in real time. The subtraction procedure is found to cope better with this problem. The subtraction procedure was developed some two decades ago, and almost totally eliminates power-line interference from the ECG signal. This procedure does not affect the signal frequency components around the interfering frequency. Digital filtering is applied on linear segments of the signal to remove the interference components. These interference components are stored and further subtracted from the signal wherever non-linear segments are encountered. Results: Modifications of the subtraction procedure have been used in thousands of ECG instruments and computer-aided systems. Other work has extended this procedure to almost all possible cases of sampling rate and interference frequency variation. Improved structure of the online procedure has worked successfully regardless of the multiplicity between the sampling rate and the interference frequency. Such flexibility is due to the use of specific filter modules. The subtraction procedure has largely proved advantageous over other methods for power-line interference cancellation in ECG signals.

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Ecg Holter Systems - Development and Perspectives

A company profile of a very small hi-tech company is presented along with the description of thei... more A company profile of a very small hi-tech company is presented along with the description of their successful product 'Ambulatory digital ECG recording and analyzing system (Holter method)'. Future trends of the field are discussed. Some observation in creating and developing a successful small hi-tech company are presented.

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BioMedical Engineering OnLine BioMed Central

Removal of power-line interference from the ECG: a review of the subtraction procedure

Generalised Subtraction Procedure for Removing PowerLine Interference from ECG : Case of Powerline Frequency Deviation

The present work continues the generalisation of the subtraction procedure, which removes the pow... more The present work continues the generalisation of the subtraction procedure, which removes the power-line interference without affecting the components intrinsic to the ECG. It is based on previous investigations, dealing separately with the cases of odd and even multiplicity/non-multiplicity between the sampling rate and the power-line frequency. The study proposes a common equations and algorithm for the cases of power-line frequency deviation. The theoretical conclusions are implemented in a program written in MATLAB environment. The algorithm and the program are tested by many particular cases and the introduced errors are evaluated. The work represents a suitable platform for accurate investigation, analysis and development of the subtraction procedure.

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Experimental Comparison of Small Wideband Magnetic Loops

In previous article “Wideband Active Small Magnetic Loop Antenna” [1] it was pointed out that the... more In previous article “Wideband Active Small Magnetic Loop Antenna” [1] it was pointed out that the wideband loop sensitivity can be increased if the short circuit current of the loop is increased, since the wideband loop is loaded with amplifier with low input resistance Rin where ωL >> Rin. Further analysis show that this current depends only from the loop factor M = A / L (see Appendix I and II) where A is the loop equivalent area and L is the loop inductance. The quantity M in some sense is an equivalent to what is the effective height quantity h for dipole antennas. In order to decrease the loop inductance and to increase the loop area, parallel loop connection was considered. It can be achieved in 2 ways with parallel loops e.g. forming a rectangular prism as shown on Fig.2 & 3 and coplanar crossed 1 (CC) loops (Fig.1 & 5) connected in way to add the loop currents into the load (cross connection [1,2] ). There might be also mixed approach –coplanar and parallel as shown in...

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Ecg Holter Systems - Development and Perspectives

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Subtraction Method for Power-Line Interferences Removal from ECG Signals: Creation and Development

Engineering Sciences, 2019

Резюме. Настоящата статия представя създаването и развитието на субтракционния метод, отстраняваш... more Резюме. Настоящата статия представя създаването и развитието на субтракционния метод, отстраняваш смущения на захранващата мрежа от електрокардиографски (ЕКГ) сигнали. Методът се състои от три основни етапа: (i) ЕКГ сигналът се разделя на линейни и нелинейни участъци; (ii) върху линейните участъци се прилага осредняващ цифров филтър, който отстранява мрежовото смущение от тях, а смущението се запомня във временен буфер; (iii) за нелинейните участъци се извършва изчисляване на смущението от временния буфер и се изважда от сигнала. Усъвършенстването на субтракционния метод се състои в несинхронизирано прилагане при произволни честоти на дискретизация и на мрежово смущение, в компенсиране на честотни и амплитудни промени в смущението, както и прилагането му при високочестотно дискретизиран ЕКГ сигнал. Ключови думи: ЕКГ сигнал, мрежово смущение, цифрово филтриране.

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Algorithm For Optimal Linear Transformation of 4 Holter Leads for Emphasizing Difference Between Typical and Atypical QRS Complexes

An optimal lead is derived by linear transformation of the available primary lead signals, which ... more An optimal lead is derived by linear transformation of the available primary lead signals, which maximizes certain criteria for distinction of an atypical beat from the typical ones. In this new ECG lead the atypical beats are enhanced and can be distinguished easily from the typical ones. A new fast algorithm for calculation of the optimal transformation is suggested which reduces substantially the number of transformation iterations. The method is compared to the original 'full combination set' method and similar results are obtained. This algorithm reduces drastically the calculation time and now standard 12-leads ECG preprocessing can be performed in reasonable time. Some preliminary results with standard 12-lead preprocesing are given.

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Removal of power-line interference from the ECG: a review of the subtraction procedure

Biomedical engineering online, 2005

Modern biomedical amplifiers have a very high common mode rejection ratio. Nevertheless, recordin... more Modern biomedical amplifiers have a very high common mode rejection ratio. Nevertheless, recordings are often contaminated by residual power-line interference. Traditional analogue and digital filters are known to suppress ECG components near to the power-line frequency. Different types of digital notch filters are widely used despite their inherent contradiction: tolerable signal distortion needs a narrow frequency band, which leads to ineffective filtering in cases of larger frequency deviation of the interference. Adaptive filtering introduces unacceptable transient response time, especially after steep and large QRS complexes. Other available techniques such as Fourier transform do not work in real time. The subtraction procedure is found to cope better with this problem. The subtraction procedure was developed some two decades ago, and almost totally eliminates power-line interference from the ECG signal. This procedure does not affect the signal frequency components around the...

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A Quantitative Estimation of Proximity between ECG Waveforms

Advances in Biomedical Measurement, 1988

Two quantities are used most often to compare the proximity (or similarity) of digitised ECG wave... more Two quantities are used most often to compare the proximity (or similarity) of digitised ECG waveforms: the correlation coefficient r and the normalised mean-square distance D. This latter quantity will be referred to as “distance”. The formulae for r and D are shown in Fig. 1. The same figure shows two ECG waveforms, A(i), B(i), and the values r and D calculated for them. Further on we shall assume that the waveforms we compare are aligned so that there is no time shift between them. That means that the corresponding points i from A(i) and B(i) belong to the same phase of the cardiac cycle.

A microprocessor-electrocardiograph

Medical & Biological Engineering & Computing, 1985

ABSTRACT

Amplification of biosignals by body potential driving

Medical & Biological Engineering & Computing, 1982

Without Abstract

Subtraction of 50 Hz interference from the electrocardiogram

Medical & Biological Engineering & Computing, 1984

Without Abstract

A Quantitative Estimation of Proximity between ECG Waveforms

Receiving Phased Array with Small Electric or Magnetic Active Wideband Elements. Experimental Performance Evaluation

The phased directional antennas have been used for years for transmitting and receiving. Active r... more The phased directional antennas have been used for years for transmitting and receiving. Active receiving phased arrays have been used in large arrays projects for scientific [25, 26] and military purposes. There are numerous scientific, commercial and amateur publications on these topics [6 to 25]. The demand in the amateur community for small sized directive antennas on lower frequencies is obvious. Here I am trying to answer several questions whose answer I could not find in the papers or in commercial documentation to which I have access. What are the practical limitations for very small sized phased arrays with active elements and can we predict and calculate their parameters ? I am not a professional in this field and instead of trying to find the proper paper, book or document which might exist somewhere in the information space I tried, with the help of some fundamental books [1, 2], simple reasoning and simple experiments to answer quantitatively some of these questions.

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