Unconstrained respiration and heart rate monitoring system based on a PPG pillow during sleep.

In this paper, we have suggested a novel method to monitor respiration and heart rate using a PPG pillow during sleep. The proposed method employs a pillow containing a reflective type PPG sensor and a simple extraction algorithm. The PPG pillow was placed under the back of a neck to acquire PPG signal on the assumption that the subjects hardly change their position. The results showed considerable coincidence between the extracted respiratory rhythm and the reference signal in case of either a medium or a high respiration speed, while it was hard to extract the rhythm based on the trace line formed by linear interpolating the detected valleys under the condition of a low respiration speed. HRV could be alternative to the interpolated trace line in the case. This study shows the proposed method has an advantage of processing simplicity so as to be used easily in unconstrained respiration and heart rate monitoring.