“…• PPG: onset, systolic, notch, and diastolic peaks • VPG: u, v, and w peaks • APG: a, b, c, d, and e peaks Photoplethysmogram is recorded using a pulse oximetry device, which is sensitive to skin structure (color), skin temperature, electrical noise, motion artifacts, and measuring environment (9). PPG is also significantly affected by the physiological variability of aging, hypertension, diabetes, vessel compliance, and apnoeic episodes (10). These have caused the peak detection of PPG to become challenging.…”