Study Of Diastolic Decay Time Constant From Photoplethysmographic Pulse

The photoplethysmogram of a pulse wave (PPG) contains abundant pathophysiological in-formation about human cardiovascular system. Contemporary investigations were almost based on the magnitude with no physiological significance, and overlooked the morphological param-eters associated with cardiovascular system. The decay time constant is a helpful morphological parameter in vascular disease assessment, such as atherosclerosis. However, conventional methods could not achieve a satisfactory estimation for no pressure and/or flow acquisition from PPG, or approach failure easily.Thus, the thesis aims to propose a novel non-iterative method (NSM) for estimating the decay time constant based on the shape of PPG pulse. The main jobs are as follows:1,Choose the one-order Windkessel model to describe PPG for the third-order Windkessel model has great complexity and weak adaptability by simulation study.2,Approve that the decay time constant depends on the morphology of diastolic PPG pulse based on simulation experiment; Compare the previous estimation methods and concluded that only fitting method appeared feasible, but non-optimal out of the concomitant problem of convergence.3,Establish a mathematic expression between RC and a novel morphological parameter called the area difference ratio (ADR) from PPG, and estimate the decay time constant by ap-plying piecewise linear interpolation criterion.4,Verify the accuracy and feasibility of the method on simulation and human experiments. Simulation errors are less than±3%. Compare the behavior of the NSM with that of the fitting method, and discover that the NSM was computationally efficient while maitaining a slightly lower fitting degree than the fitting method which is used as a reference method.NSM is superior to other previous method and not need precaliberation or normalization.