Evaluation of key design parameters for mitigating motion artefact in the mobile reflectance PPG signal to improve estimation of arterial oxygenation.

Objective: Pulse oximetry, a widely accepted method for non-invasive estimation of arterial oxygen saturation (SpO) and pulse rate (PR), is increasingly being adapted for mobile applications. Previous work in mitigating motion artefact, which corrupts the photoplethysmogram (PPG) used in pulse oximetry, has focused on reducing noise using signal processing algorithms or through sensor design that controlled only one variable at a time. In this work, we have investigated the effect of several variables such as sensor weight, relative motion, placement, and contact force against the skin that can impact motion artefact independently or by interacting with each other.

Approach: We have identified a unique combination of these variables that is most optimal in reducing motion artefacts using a full factorial design of experiments methodology and evaluated the effect of these factors on PPG readings with and without motion.

Main Results: Data collected on 10 diverse subjects showed that placement (p  =  0.03), contact force (p  =  0.004), and sensor-to-skin adhesion or relative motion when combined with force (p  <  0.001) had the most significant effect on reducing the motion artefact signal. Sensor weight (p  =  0.822) by itself had no significant effect, however when combined with sensor adhesion (p  <  0.001) had a significant impact.

Significance: This lays the foundation for future development of more robust sensors that can significantly reduce the effect of motion artefacts in reflectance-based pulse oximetry and could have great clinical value due to significant reduction of SpO errors and false alarms associated with motion artefact, making wearable pulse oximetry more reliable in mobile applications.