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. Author manuscript; available in PMC: 2022 Mar 21.
Published in final edited form as: Am J Physiol Heart Circ Physiol. 2021 Dec 24;322(4):H493–H522. doi: 10.1152/ajpheart.00392.2021

Figure 5. Extracting features from photoplethysmogram (PPG) pulse waves.

Figure 5

Features can be extracted from a single PPG pulse wave in two steps: A) identifying fiducial points on the pulse wave, such as systolic (sys) and diastolic (dia) peaks, dicrotic notch (dic), early and late systolic peaks (p1 and p2), the slope of the rising front (ms), and a, c, e peaks and b and d troughs of the 2nd derivative; and B) calculating features from the amplitudes and timings of these points, such as the time from pulse onset to sys (CT), the time from sys to dia (DT), the reflection index (RI), the maximum upslope (ms), and the slope between b and d troughs (slopeb-d). Sources: A: P.H. Charlton, “Photoplethysmogram (PPG) pulse wave fiducial points” (https://commons.wikimedia.org/wiki/File:Photoplethysmogram_(PPG)_pulse_wave_fiducial_points.svg) (CC BY 4.0); B: P.H. Charlton, “Photoplethysmogram (PPG) pulse wave indices (https://commons.wikimedia.org/wiki/File:Photoplethysmogram_(PPG)_pulse_wave_indices.svg)” (CC BY 4.0).