Taylor-Fourier Analysis of Photoplethysmography Signals for Heart Rate Measurement

Photoplethysmography (PPG) is gaining increasing attention for the measurement of heart rate (HR) and heart rate variability (HRV), but the accuracy and reliability of measurement results remain questionable when obtained from wearable devices, prone to recording movement artifacts and other disturbances caused by poor sensor-skin contact. HR and HRV information is typically extracted in the time domain, from the estimation of inter-beat intervals, which can be confidently identified only when the signal is very clean. This paper proposes an alternative time-frequency approach to the HR estimation and to the signal quality assessment, based on the Taylor-Fourier Transform, capable of retrieving time-varying amplitudes and phases of the spectral components in non-sinusoidal, quasi-periodic signals. Preliminary results from a healthy subject show good promise for this method in the identification of disturbances within the signal and in the estimation of the instantaneous HR, at least in clean parts of the signal. A full validation of the proposed method remains outside the scope of this paper, but directions for future research are discussed.