A New Look at the Essence of the Array Photoplethysmograph

Photoplethysmography (PPG) has been widely used to investigate various cardiovascular conditions. Previous studies have demonstrated the effects of temperature of the measurement environment. However, an integrated evaluation has not been established in environments with gradual air temperature variations. This study was conducted to determine the correlation between the activity frequency (AF) of array PPG image and the changes in skin surface temperature (SST) by environment temperature control. The study participants were 13 company employees aged between 27 and 48 years (mean age: 35.6 years) who were treated with an IR heater to increase the skin temperature for approximately 15 min. Measurements of finger array PPG and finger SST were obtained before infrared heating as baseline, and the intervention of 15-min infrared heating was continued in the left hand as the experiment group. The right hand was not subjected to heating, which served as the control group. The results showed that the local fingertip SST increase affected the local AF of the array PPG image, which could be related to the biphasic skin blood flow response. The array PPG image could be used for monitoring the activity control of microcirculation or endothelial function.