SIMPLE AND ACCURATE WAY FOR ESTIMATING TOTAL AND SEGMENTAL ARTERIAL COMPLIANCE - THE PULSE PRESSURE METHOD

We derived and tested a new, simple, and accurate method to estimate t he compliance of the entire arterial tree and parts thereof. The metho d requires the measurements of pressure and flow and is based on fitti ng the pulse pressure (systolic minus diastolic pressure) predicted by the two-element windkessel model to the measured pulse pressure. We s how that the two-element windkessel model accurately describes the mod ulus of the input impedance at low harmonics (0-4th) of the heart rate so that the gross features of the arterial pressure wave, including p ulse pressure, are accounted for. The method was tested using a distri buted nonlinear model of the human systemic arterial tree. Pressure an d flow were calculated in the ascending aorta, thoracic aorta, common carotid, and iliac artery. In a linear version of the systemic model t he estimated compliance was within 1% of the compliance at the first t hree locations. In the iliac artery an error of 7% was found. In a non linear version, we compared the estimates of compliance with the avera ge compliance over the cardiac cycle and the compliance at the mean wo rking pressure. At the first three locations we found the estimated an d ''actual'' compliance to be within 12% of each other. In the iliac a rtery the error was larger. We also investigated an increase and decre ase in heart rate, a decrease in wall elasticity and exercise conditio ns. In all cases the estimated total arterial compliance was within 10 % of mean compliance. Thus, the errors result mainly from the nonlinea rity of the arterial system. Segmental compliance can be obtained by s ubtraction of compliance determined at two locations.