Comment on 'Pulse rate variability in cardiovascular health: a review on its applications and relationship with heart rate variability'.

Precise beat-to-beat fiducial point detection in the photoplethysmogram signal is essential for reliable pulse rate variability (PRV) analysis, which is considered an integral part of health monitoring devices in the evolving era of mobile health. Several studies have aimed to compare PRV to the well-investigated, gold standard heart rate variability (HRV) analysis, to see if they are interchangeable. The agreement between PRV and HRV is not unequivocal, as we learn from the commented metaanalysis. Technical factors like low sampling rate of photoplethysmography (PPG) or imprecise fiducial point detection are more important in this difference than physiological factors corresponding to pulse arrival time. Standardization of the PPG acquisition and reference point detection is necessary for comparable studies and correct measurement.