Fig. 1
From: Photoplethysmography parameters in monitoring nociception during general anesthesia
Waveform characteristics of a PPG and parameter diagram
T: the trough of a PPG. P: the peak of a PPG. T’: the next trough. O: the vertical projection of point P on the TT line
TP: the anacrotic phase. PT’: the catacrotic phase. TT’: the overall phase. t0-t1: the interval of anacrotic phase. t1-t2: the interval of the catacrotic phase. t0-t2: the interval of the overall phase
PPGA: the amplitude of OP; PBI: the interval of TT’; SPI was computed as a combination of the normalized PPGA and heart beat interval (HBI), SPI = 100-(0.7*PPGAnorm+ HBInorm)