Optical flow sensor as a reference for reduction of motion artefacts in photoplethysmographic measurements

Methods commonly used for reduction of motion artefacts in photoplethysmography employ accelerometry as a reference for adaptive filtering and signal processing. In this paper, we propose the use of an optical flow sensor to measure the relative displacement between a photoplethysmographic sensor and the measurement site. In order to evaluate the performances of this novel method, a wrist-worn device that enables simultaneous acquisition of physiological information and relative motion has been developed. The optical flow sensor provides a two-dimensional information source correlated with artefacts contained in the cardiac frequency band. Preliminary results show a clear correlation between motion recorded by the sensor and artefacts contained in the photoplethysmographic signal. In association with adaptive filtering, the proposed technique shows efficient reduction of motion artefacts during physical activity.