Calculation and Validation of Continuous Pulse Transit Time Based on Normalized Pulse Wave Velocity

Typically, the pulse transit time (PTT) is extracted as a discrete value per heartbeat: it is calculated as the time difference between specific points of the pulse waveforms measured at two different sites. However, this is not a perfect representation because a pulse wave propagates continuously. In this study, we propose a method to determine the continuous PTT (CPTT) by calculating consecutive time delays of photoplethysmography (PPG) waveforms measured at the fingers and toes of 14 young, healthy volunteers. The proposed CPTT is calculated as the average time delay determined by moving the segmented PPGs and has a correlation of 0.744 with conventional PTT. In addition, the proposed CPTT showed a −0.712 correlation coefficient (P < 0.001) with the continuous pulse-wave velocity derived from the continuous blood pressure waveform. These results suggest that the proposed CPTT is a promising indicator for pulse-wave velocity estimation.