Modeling of photoplethysmography signal for quantitative analysis of endothelial cells during reactive hyperemia

In this study, at first the cardiovascular system is modeled based on the 1D method and then the simulation of the reactive hyperemia experiment has been applied on the model. In this simulation, by applying a cuff at the brachial artery, the flow downstream of the cuff is occluded. Then with releasing the cuff immediately, a large amount of shear stress, about 4 times the basal amount, is applied downstream of the cuff and consequently to the endothelial cells in a very short moment. Considering a reported experimental transfer function between shear stress and vasodilation, the increase of the artery diameter due to the sudden increase of the shear stress is obtained. Finally, the photoplethysmography (PPG) signal variation after releasing the cuff is calculated. By studying the method of the variation of this signal in the clinical experiment for a group of healthy people and people with hypercholesterolemia disease, it has been clear that a parameter related to the PPG signal variation can be determined, so that this obtained parameter can discrete these two groups. Comparing the caculated parameter obtained from the signal variation from the model, it was found that the current model results are similar to the healthy group.