Photoplethysmogram Technique to Characterize the Carotid-to-toe Pulse Duration during Different Human-postures

Photoplethysmogram, including Pulse Transit Time (PTT), technique were used to detect blood volume changes in human carotid-to-toe. The main problem is how to evaluate the PTT values continuously from the subject with accurate readings. Monitoring PTT values of a person is useful in non-invasive, cuff-less estimation of blood pressure measurement. In this study, PTT values of 12 healthy subjects (8 males and 4 females) age 23.8 ± 1.5 years have been estimated using an auto-regressive with exogenous input (ARX) model. We presented autoregressive model for single variant and multi-variant model, using time series model, taken into account exogenous variables, a locally constant autoregressive model, and a radial basis function autoregressive model. We implemented the time domain system identification using an autoregressive with exogenous input (ARX) model. PTT values were estimated for all subjects in three different positions; sit, stand and supine. Results show that the PTT in sit and stand positions are statistically no different (84.5±19.6 ms versus 78±15.9 ms, p = 0.44). However, the PTT in the supine position is significantly higher than the two other positions (145.7±18.4 ms versus 84.5±19.6 ms and 145.7±18.4 ms versus 78±15.9 ms respectively, p < 0.01 for both situations). These results concur with values reported by other researchers (120 ms < PTT < 180 ms) on the effect of posture in estimating PTT.