PTT was defined as the time interval between the R-peak of ECG and the characteristic point of the pulse wave. The principle of PTT can be represented as shown in Fig. 2. Fig. 2(a) indicates ECG signal, Fig. 2(b) PPG signal, and Fig. 2(c) pressure pulse wave signal. The measured PTTPPG implies the time interval between the R-peak of ECG and the characteristic point of PPG signal. PTTpressure implies the time interval between the R-peak of ECG and the characteristic point of the pressure pulse wave signal.