Using the multi-parameter variability of photoplethysmographic signals to evaluate short-term cardiovascular regulation

Transient changes in cardiovascular regulatory activities are valuable for clinical monitoring and pathophysiological research. However, there is a lack of effective methods to evaluate short-term cardiovascular regulation. This study explores a photoplethysmography (PPG)-based multi-parameter analytical approach using the period, amplitude and baseline of PPG signals to quantitatively assess cardiovascular regulation over a 30 s period. PPG data were recorded from 31 young healthy subjects during conditions of spontaneous respiration, paced respiration with 15 breaths/min and breath holding, with each condition lasting 30 s. The three indices (SD1, SD2, SD1/SD2) in Poincaré plot of the normalized parameters and the correlations between the parameters or the first differences of the parameters were analyzed. The results showed that compared with spontaneous respiration, SD1 of PPG amplitude increased significantly but the correlations between any two parameters or between the first differences of any two parameters decreased significantly during paced respiration; SD1 and SD1/SD2 of all PPG parameters as well as the correlations of the first differences between any two PPG parameters reduced significantly during breath holding. The results indicate the respiratory induced alterations in cardiovascular autonomic function could be identified by the variability of various PPG parameters or their correlations over 30 s periods. Moreover, the indicators used to quantify the variability of the PPG parameters in this study may provide a feasible and effective way to evaluate short-term cardiovascular regulation.