Evaluation of wavelets for reduction of motion artifacts in photoplethysmographic signals

Photoplethysmographic (PPG) signals obtained at Red and Infrared wavelengths are utilized in pulse oximetry for estimation of arterial blood oxygen saturation (SpO₂). Mostly inaccurate readings in a pulse oximeter arise when PPG signals are contaminated with motion artifacts (MA) due to the movement of patient and hence MA are a common cause of oximeter failure and loss of accuracy. This paper presents performance evaluation of different wavelets for the reduction of MA. Test results on the PPG signals recorded with frequently encountered artifacts (viz., horizontal, vertical and bending motions of finger) reveal that the estimated Spo₂ values from MA reduced PPGs using different wavelets are very close to each other. In addition, the Daubechies wavelet interestingly kept the respiratory information intact while effectively removing the MA from PPG signals. Hence, the work establishes that the Daubechies wavelet is the most preferred wavelet for pulse oximetry applications.