Motion Artifact Cancellation in Wearable Photoplethysmography Using Gyroscope

Wearable reflectance-type photoplethysmography (PPG) sensors, in the form of a band or watch, have recently gained significant attention for real-time heart rate (HR) monitoring applications. To accurately estimate the HR, even during intensive exercise, much effort has focused on simultaneously measured accelerometer signals that cancel out motion artifacts (MAs) from the PPG signal. However, the accelerometer does not always measure true MAs, as it measures not only the acceleration of motion but also gravitational acceleration corresponding to each axis of the accelerometer. In addition, the measured acceleration of the motion itself does not always coincide with the true motion. In this paper, we address the limitations of accelerometers and present an approach using a gyroscope to overcome the issues described. To the best of our knowledge, the limitations of the acceleration signals for MA cancellation have not been addressed in-depth. Here, we describe our developed wearable reflectance-type PPG sensor and compare the HR estimation performance between using a gyroscope and an accelerometer from 24 subjects. Our results showed that the gyroscope-assisted approach exhibited better performance than the accelerometer-assisted approach, especially for an exercise involving walking.