A Multi-Site, Multi-Wavelength PPG Platform for Continuous Non-Invasive Health Monitoring in Hospital Settings
Stefan Karolcik, Damien Ming, Sophie Yacoub, Alison Holmes, Pantelis Georgiou
Abstract
This paper presents a novel PPG acquisition platform capable of synchronous multi-wavelength signal acquisition from two measurement locations with up to 4 independent wavelengths from each in parallel. The platform is fully configurable and operates at 1ksps, accommodating a wide variety of transmitters and detectors to serve as both a research tool for experimentation and a clinical tool for disease monitoring. The sensing probes presented in this work acquire 4 PPG channels from the wrist and 4 PPG channels from the fingertip, with wavelengths such that surrogates for pulse wave velocity and haematocrit can be extracted. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">For conventional PPG sensing, we have achieved the mean error of 4.08 <inline-formula><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 3.72 bpm for heart-rate and a mean error of 1.54 <inline-formula><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 1.04% for SpO<sub>2</sub> measurement, with the latter lying within the FDA limits for commercial pulse oximeters. We have further evaluated over 700 individual peak-to-peak time differences between wrist and fingertip signals, achieving a normalized weighted average PWV of 5.80 <inline-formula><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 1.58 m/s, matching with values of PWV found for this age group in literature. Lastly, we introduced and computed a haematocrit ratio (<inline-formula><tex-math notation="LaTeX">$R_{hct}$</tex-math></inline-formula>) between the deep IR and deep red wavelength from the fingertip sensor, finding a significant difference between male and female values (median of 1.9 and 2.93 respectively) pointing to devices sensitivity to Hct.