Influence of Light Intensity on a Motion Artifact Signal in a Photoplethysmographic Signal

Abstract

A photoplethygraphic (PPG) signal acquired from a commercial pulse oximeter is habitually disfigured by a motion artifact (MA) signal while any motion takes place. Inherently, the MA signal can either be additive or multiplicative, By having the MA signal intertwined with the PPG signal, the estimate of the oxygen saturation (SpO2) value is unreliable. The computation of SO2 value is based on proper red and infrared (IR) PPG signals measured by the pulse oximeter. Generally, the frequency components of the red and IR PPG signals as well as the MA signal are in the same range. To overwhelm this problem, the frequency components of the red and IR PPG signals are severed from the frequency band of the MA signal. To implement the separation, a legacy source of driving red and IR LEDs in the pulse oximeter is replaced by two alternating current sources having different frequencies. With this solution, the additive MA signal is no longer involved but the multiplicative MA signal is yet not concluded. In this work, change in light intensity fed to both red and IR LEDs is studied whether the changed light intensity has any impact on the multiplicative MA signal. According to the study, it is found that change in light intensity does not affect the multiplicative MA signal. The multiplicative MA signal still exists since the overall calculated SpO2 values have some error up to 1 %. Besides, change in light intensity does not improve the quality of the estimated SpO2 values while resting.