Fig. 1
A typical photoplethysmography (PPG) waveform response during the Valsava maneuver: a Before hemodialysis and b After hemodialysis. Pulse amplitude ratio (PAR) is calculated as the pulse amplitude of the waveform at the end of 10 s of Valsalva (PAV) divided by the average pulse amplitude of several cycles at baseline (PAB). In this example, PAR = 0.81 before hemodialysis and PAR = 0.67 after hemodialysis. The automated algorithm acquiring the data allows a maximum of 3 s for the subject’s expiratory effort to equal or exceed 20 mmHg in order for the data to be accepted and stored