A two step Gaussian modelling to assess ppg morphological variability induced by psychological stress

Abstract

In the present work, we analyse characteristic features of the pulses photoplethysmographic (PPG) signal and their changes and evolution during various psycologically stressed conditions. Acute psychological stress was induced to subjects using a modified version of Trier Social Stress Test. It was revealed that the morphology of the PPG pulses is different during the streneous sessions from that of the relaxed one and possibly reflect arterial stiffness variations which can be a marker for differentiation of the stressed stages from the relaxed stage of the protocol. Since, the PPG pulse formation is due to the superimposition of a systolic and a reflected wave, a novel two step Gaussian mixture modelling technique was used to extract their relative arrival time and width. Position (B1,B2) and width (C1,C2) of the systolic and reflected wave are the relevant features studied along with the time to reflection (T12). Significant statistical differences were observed in B1(p < 0.001), B2(p < 0.05), C1(p < 0.001), C2(p < 0.05) in the relaxed and stressed session. These results suggest changes in the morphology of PPG pulses possibly revealing marks of arterial stiffness occurring due to psychological stress.