Fig. 1.

Key features of blood pressure estimation using PPG and other physiological signals. (i) Using PPG signal and its derivative, (ii) using ECG and PPG signals, (iii) using BCG signals and PPG signals, and (iv) using PCG and PPG signals. Here, PPG photoplethysmogram, APG acceleration photoplethysmogram, BCG ballistocardiogram, PCG phonocardiogram, STT slope transit time, PTT pulse transit time, PEP pre-ejection period, PAT pulse arrival time, TD time interval between the J peak in the BCG signal and the systolic peak in the PPG signal, VTT vascular time interval between the first heart sound S1 and the systolic peak in the PPG signal, S1 first heart sound, S2 second heart sound