Non-invasive measurement of arterial pressure-dependent compliance

Pressure-dependent compliance is able to better reflect the degree of the arterial tree stiffness. Many researchers apply Windkessel model to evaluate compliance of the arterial tree. However, this model assumes that the compliance is not related to the blood pressure, which is not valid for the high pressure situation, thus this paper proposed an improved nonlinear model for analyzing the pressure waveform obtained from human radial artery with a precise pressure waveform acquisition device. The electrical model for analysis in this study mainly contains a nonlinear capacitor that simulates the nonlinear pressure-dependent compliance of the whole human arterial tree and a resistor that simulates flow resistances of the small arteries and arterioles. Since the nonlinear pressure-dependent compliance C(p) is determined by blood pressure p(l), the relation between compliance and blood pressure of human arterial tree is expressed as C(p)=a center dot exp(-b center dot p(t)), where the parameters a and b are constants determined from curve fitting of experimentally measured radial artery pressure waveform. Besides localization and data collection, the acquisition device can also provide a preset pressure on the radial artery before measurement and hold this pressure during measurement. The pressure waveform obtained from the device, then, is calibrated by blood pressure measured using clinical sphygmomanometer. The pressure waveform after calibration is segmented into a series of single-cycle waveforms using a threshold algorithm. For each single-cycle waveform, the dicrotic notch is identified, which indicates the start of the diastolic period. After diastolic waveform identification of each single-cycle waveform, the optimal a and b are determined by curve fitting of each diastolic waveform. The nonlinear compliance C(p) shows the relationship between arterial tree compliance and blood pressure, which is very useful for physicians to diagnose arteriosclerosis and hypertension, and provides a new perspective to the understanding of cardiovascular diseases. Experiment has been carried out to evaluate the pressure-dependent compliance. The results have been provided.