Near-infrared iPPG body motion compensation using head Euler angles during sleep

Image photoplethysmography (iPPG) is a non-invasive and non-contact method that can measure the heart rate (HR) of a person while sleeping without causing discomfort. However, the iPPG signal can be contaminated by body motion, making HR measurement difficult. Therefore, body motion noise caused by tossing and turning during sleep can cause sections where HR cannot be measured. Thus, we propose a method of recovering the iPPG signal contaminated by body motion using the x and y coordinates of the region of interest in the face and the Euler angle of the head. The proposed system reduces the influence of tossing and turning during sleep and improves the accuracy of HR measurement. In our experiment, subjects were instructed to sleep at stationary and mixed body movement positions (turning every 15 s) in an environment designed for sleeping. The experimental results confirmed that the HR measurement accuracy was improved over conventional methods both at rest and when body motions occurred.