Position Dependency in Photoplethysmographic sensor -Comparison of adjoining PPG signals in Light Sources and Measurement Sites-

This study examined position dependency in photoplethysmography (PPG). For transmitted-light PPG, a sensor is usually attached on a fingertip and transmitted light is monitored. Although simple to use, a fingertip sensor and transmitted-light PPG cannot monitor vital signs during exercise and daily activities because the sensor attachment becomes disturbed. Reflected-light PPG can be applied to any part of the body. However, differences in cutaneous blood supply to different regions have been reported, and the accuracy of measurements can vary among neighboring sites. This position dependency can cause the pulse count to fail and necessitate sensor reattachment. The light source can also affect the characteristics of reflected-light PPG. To investigate position dependency in PPG, we compared the reflected light signals obtained from green and infrared PPG sensors at different sites. Eight young healthy subjects were recruited to participate in the study. Green and infrared PPG signals were collected simultaneously from three sites on the left arm of each participant. The correlations among adjoining green PPG signals were higher than those among adjoining infrared signals. Furthermore, the difference in the pulse interval was smaller among adjoining green PPG signals than among infrared signals. These results suggest that green-light PPG has less position dependency and thus may be more suitable for monitoring the pulse rate during daily activities.This study examined position dependency in photoplethysmography (PPG). For transmitted-light PPG, a sensor is usually attached on a fingertip and transmitted light is monitored. Although simple to use, a fingertip sensor and transmitted-light PPG cannot monitor vital signs during exercise and daily activities because the sensor attachment becomes disturbed. Reflected-light PPG can be applied to any part of the body. However, differences in cutaneous blood supply to different regions have been reported, and the accuracy of measurements can vary among neighboring sites. This position dependency can cause the pulse count to fail and necessitate sensor reattachment. The light source can also affect the characteristics of reflected-light PPG. To investigate position dependency in PPG, we compared the reflected light signals obtained from green and infrared PPG sensors at different sites. Eight young healthy subjects were recruited to participate in the study. Green and infrared PPG signals were collected simultaneously from three sites on the left arm of each participant. The correlations among adjoining green PPG signals were higher than those among adjoining infrared signals. Furthermore, the difference in the pulse interval was smaller among adjoining green PPG signals than among infrared signals. These results suggest that green-light PPG has less position dependency and thus may be more suitable for monitoring the pulse rate during daily activities.