Monitoring of heart and respiratory signals with PPG in bathing

Bathing is a common custom in Japan. Therefore, physiological measurement during bathing can be useful for monitoring a daily routine. Here, a measurement technique using a photoplethysmograph (PPG) during bathing is presented. A PPG signal was obtained from a waterproofed probe that was attached to the bottom surface of an inner wall of a bathtub. The PPG signals were filtered with a low-pass filter, then the respiration components were extracted. The PPG signals were measured during bathing in 10 healthy male subjects and respiratory signals can be obtained from PPG signals