Orthostatic stress and area under the curve of photoplethysmography waveform

Background. Recent studies have shown that shape and morphology of photoplethysmography (PPG) waveform can provide useful information about cardiovascular system. These parameters namely pulse amplitude, pulse width, pulse rise time and pulse reflected delay have been studied independently and there is information about the interaction of these parameters. There is no detailed description of calculating these parameters. We have described a detailed algorithm for calculating these parameters. We also investigated a new parameter calculated using area under the curve of PPG waveform (AUCPPG). All parameter were calculated using finger probe oximeter sensor from 22 subjects before and after orthostatic stress. Changes in AUCPPG were compared against pulse interval, amplitude, width, rise time of PPG pulse and pulse reflection delay (PRD). Results. We found that all parameters showed a decrease with orthostatic stress. PPG pulse width parameter was very inconsistent and changed significantly based on small change in shape of PPG waveform. AUCPPG showed strong correlation with pulse amplitude ( r 0.85) in supine position, but that relationship decreased in upright position ( r 0.64) as reflected peaks became more distinct and separated. Multivariable regression showed that PRD and rise had negative influence on AUCPPG. Male subjects showed higher AUCPPG values. Conclusion. We conclude that all PPG based parameters are effected by subject’s position. Although AUCPPG is correlated with PAP width, it is an independent parameter that can be calculated more consistently than pulse width. From the results of our sample population we conclude AUCPPG is a better indicator of change in vascular tone than PAP amplitude or PAP width. Unlike other parameters AUCPPG incorporates the influence of both PAP and reflected waves.