Pre-processing of the photoplethysmography (PPG) signal plays an important role in the analysis of the pulse wave signal. The task of pre-processing is to remove noise from the PPG signal, as well as to transmit the signal without any distortions for further analysis. The integrity of the pulse waveform is essential since many cardiovascular parameters are calculated from it using morphological analysis. Digital filters with infinite impulse response (IIR) are widely used in the processing of PPG signals. However, such filters tend to change the pulse waveform. The aim of this work is to quantify the PPG signal distortions that occur during IIR filtering in order to select a most suitable filter and its parameters. To do this, we collected raw finger PPG signals from 20 healthy volunteers and processed them by 5 main digital IIR filters (Butterworth, Bessel, Elliptic, Chebyshev type I and type II) with varying parameters. The upper cutoff frequency varied from 2 to 10 Hz and the filter order—from 2nd to 6th. To assess distortions of the pulse waveform, we used the following indices: skewness signal quality index (S_SQI), reflection index (RI) and ejection time compensated (ETc). It was found that a decrease in the upper cutoff frequency leads to damping of the dicrotic notch and a phase shift of the pulse wave signal. The minimal distortions of a PPG signal are observed when using Butterworth, Bessel and Elliptic filters of the 2nd order. Therefore, we can recommend these filters for use in applications aimed at morphological analysis of finger PPG waveforms of healthy subjects.

ФУНКЦИОНАЛЬНЫЕ ИССЛЕДОВАНИЯ СИСТЕМЫ МИКРОЦИРКУЛЯЦИИ КРОВИ МЕТОДОМ ЛАЗЕРНОЙ ДОПЛЕРОВСКОЙ ФЛОУМЕТРИИ В КЛИНИЧЕСКОЙ МЕДИЦИНЕ: ПРОБЛЕМЫ И ПЕРСПЕКТИВЫ

Noncoherent fluctuation spectroscopy (NFS) is described as an optical method for measuring the tissue blood perfusion. This method is based on the registration of low-frequency fluctuations of a...

Разработан первый в мире прототип автоматизированного прибора-тонометра с выносными оптическими датчиками для комплексной оценки параметров центральной и периферической гемодинамики у пациентов с сахарным диабетом. Вместе с процедурой измерения артериального давления стандартным осциллометрическим методом, за счет сочетанных оптических неинвазивных технологий с использованием окклюзионного и теплового функциональных нагрузочных тестов на систему микроциркуляции, прибор позволяет регистрировать и оценивать индекс эластичности сосудов, интегральную скорость распространения пульсовой волны, базовый тонус сосудов микроциркуляторного русла, эндотелиальную регуляцию тонуса и реактивность сосудистого...

As applied to the problems of medical laser Doppler flowmetry and based on a modified Kubelka–Munk two-flow model, analytic expressions have been obtained for the radiation power backscattered by biological tissue, taking into account the variable hyperemia of its microvasculature. An estimate is made of the power contribution of the Doppler component of the flow to the overall backscattered-radiation signal recorded by the device, which appears when light is scattered at moving erythrocytes. It is shown that the power contribution of the Doppler component to the overall backscattered radiation flux is no greater than 5% on average. The variable hyperemia that results from various physiological processes causes the radiation flux recorded by the Doppler flowmeter to be amplitude modulated. The power of the amplitude-modulated component can be of the same order of magnitude as, and in certain cases even greater than, the power of the useful Doppler signal, creating noise in the input signal of the device.