Yu. A. Bulgakov1, A.A. Mikheev2

1,2 Ryazan State Radio Engineering University named after V.F. Utkina (Ryazan, Russia)

The article discusses the issues of isolation and subsequent elimination of the isoline drift of the electrocardiosignal for cases when the width of the frequency spectrum of the isoline drift signal is comparable to the heart rate. To solve this problem, samples of the isoline drift signal are taken at the TP interval of the electrocardiosignal and transformed into complex discrete samples, suppressing the spectral components in their spectrum starting from the first spectral zone while preserving the zeroth spectral zone that contains the components of the isoline drift. The peculiarity of this process is that the sampling rate of the isoline drift signal is determined by the heart rate, which is physiologically exhibits variability, meaning the sampling rate is not constant. This, in turn, violates the suppression conditions of the selected spectral zones, and the spectral components of these zones become non-zero. Thus, the isoline drift signal allocated by the low-pass filter will be distorted by these components.

Based on the analysis of the suppression condition in the spectrum of a sequence of complex discrete samples of the selected spectral zone, it is proposed to adjust the time shifts of additional samples of the isoline drift signal relative to the main reference in proportion to the value of the sampling period, which is determined by the duration of the current heart rate cycle. This maintains a constant ratio between the time shift of additional samples of the isoline drift signal and the sampling period in each heart rate cycle, ensuring that the condition for suppressing the components of the selected spectral zone is not violated.

An algorithm for the formation of complex discrete samples of the electrocardiosignal on the TP interval in the presence of sampling period variability, which provides isolation of the isoline drift signal with an extended frequency range, has been developed. The algorithm includes actions related to measuring the duration of the current heart rate cycle, which is also the duration of the current time interval between adjacent samples of the baseline drift signal (current sampling period), determining the corresponding time shift values of additional samples, memorizing and delaying the current values of the electrocardiosignal by one heart rate cycle.

The algorithm is implemented in a programming language C# using Windows Forms technology and the ScottPlot library to visualize the results.

A program has been developed for the STM32F411 microcontroller in conjunction with the NUCLEO-F411RE debugging board, which implements the algorithm for generating complex discrete samples in real-time mode. The algorithm and program have been verified based on spectral analysis of the data obtained from executing the program, which confirmed the possibility of isoline drift signal isolation with a frequency range whose upper limit exceeds half the sampling frequency.

The proposed algorithms and software tools make it possible to generate complex discrete samples of the isoline drift signal in real time under conditions of variability of the sampling period, which provides more accurate isolation of the isoline drift signal with an extended frequency range.

Bulgakov Yu.A., Mikheev A.A. Real-time formation of complex discrete samples of the isoline drift of the electrocardiosignal under conditions of variability of the sampling period. Biomedicine Radioengineering. 2023. V. 26. № 3. Р. 79-89. DOI: https://doi.org/10.18127/ j15604136-202303-10 (In Russian).

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