Simultaneous multi-site measurement system for the assessment of pulse wave delays

A precise, multi-track system for the simultaneous, real-time measurement of electrocardiographic (ECG) and many photopletysmographic (PPG) signals is described. This system allows the calculation of pulse wave delay parameters such as pulse arrival time (PAT) and pulse transit time (PTT). The measurement system was built on a custom, real-time embedded system with multiple specific analogue-front-end devices. Signals were recorded on-line and data were processed off-line in the Matlab software. Testing of human subjects was carried out on a group of 16 volunteers. The system was capable of taking a measurement of one 24-bit ECG and eight 22-bit PPG tracks with high precision (input-referred noise 1.4 mu V for ECG and about 20 pA for PPG). All signals are sampled simultaneously (phase shift between ECG and PPG is only 1.5 ms for 250 Hz frequency sampling). Significant differences in pulse wave delays were found for the 16 subjects studied (e.g. about 100 ms for PAT on a right toe, 40 ms for differential PAT on left-right toes and about 100 ms for PTT calculated for forehead-right toe pulse wave). The proposed system provides a simultaneous and continuous evaluation of pulse wave delays for the entire arterial bed. The proposed measurement methods are comfortable and can be used for a long time. Simultaneous measurements of pulse wave delays at various sites increase the reliability of measurement and create new possibilities for medical diagnosis. (C) 2019 Nalecz Institute of Biocybernetics and Biomedical Engineering of the Polish Academy of Sciences. Published by Elsevier B.V. All rights reserved.