Effect of upper arm cuff pressure on pulse morphology using photoplethysmography

Study of Arterial pressure and flow variation when external pressure applied is critical in understanding clinical relevance of pulse. We propose a distributed model of entire human arterial tree to describe the hemodynamic changes due to pressure applied on the brachial artery. Input to this distributed model is from a four element Windkessel model. We measured the blood volume during brachial occlusion in six healthy subjects using finger photoplethysmography (PPG). We analyzed the morphological changes in both the model and the experiment. We found that both the model pressure pulse and the finger volume pulse morphology changing with the applied pressure. We calculated the normalized values of pulse height, maximum systolic slope, maximum diastolic slope and peak to peak interval (PPI) for each beat. Mean values of all the morphological parameters show an initial rise and in the model the maximum occurs at 60-80mmHg while in the experiments it occurs at 40mmHg. The predicted model parameters are positively correlated with measured parameters (for maximum systolic slope r = 0.54; for maximum diastolic slope r = 0.77; for pulse height r = 0.89 when P < 0.05). The PPI variation is different for each subject reflecting the reflex properties of the individual. Variable elastance and reflex system should be incorporated in the model to accurately predict the experimental results.