Adaptive Motion Artifact Filter for Photoplethysmogram Extraction

Abstract

Adaptive filters have been used to enable the robust measurement of photoplethysmogram (PPG) under conditions of the motion artifact which causes a high noise to the signal. In this adaptive filter a noise reference and a signal reference are used. The least mean square (LMS) method was applied to extract the actual signal from the noisy one. For the first approximation to generate the reference signal, a low pass filter is used. Based on the resulting signal, an appropriate reference signal is generated. This reference signal is in turn subtracted from the detected signal to generate a noise signal. The generated noise signal is modified to synthesize the noise reference signal. The synthesized reference noise is adjusted by the adaptive algorithm to the real one contained in the measurement, and then subtracted from the detected noisy signal. The filtered signals can be used to determine various physiological parameters such as the fractional oxygen saturation or the other blood components. Calculating the oxygen saturation using the filtered PPGs subjected to artifacts looks promising when compared to the calculated values using PPGs without motion artifacts, for the same case.