| The functional properties of the proximal arterial system involve storage and dissipation of the energy associated with pulsatile outflow from the left ventricle. A method to characterize both these properties is presented. Real power (AC), based on the product of aortic pressure and flow, measures pulsatile energy dissipation. It is demonstrated in this report that reactive power, which measures pulsatile energy storage, can be obtained using the area of the aortic pressure-flow (PQ) loop. Employing a representative model of the arterial system, it is shown that both the reactive power and the PQ loop area are proportional to the average amount of pulsatile energy that was transiently held by the capacitive element in the model when aortic flow and pressure served as the inputs.;An experimental protocol was then developed to test these latter observations in the dog. In eight experiments, direct measurements of properties representing the proximal and distal arteries, and the ventricular input were made, and the PQ/AC ratio was computed from aortic root pressure and flow. Using multiple regression, the conclusion was reached that the PQ/AC ratio was more sensitive to the proximal arteries than to the distal arteries, and that it also had an appreciable sensitivity to the heart rate. With stated qualifications, the PQ/AC ratio was proposed to serve as an index of those properties of the proximal arterial system which affect the development of pulsatile pressure and flow.;The ratio of the PQ loop area to the average pulsatile input power (PQ/AC ratio) was then proposed to serve as an index for functional changes in the proximal arteries. The sensitivity of this ratio to properties of the proximal arteries, the distal arteries, and the ventricular input was examined using computer simulation of the arterial system. It was found to be primarily sensitive to the proximal arteries, virtually insensitive to the distal arteries, and moderately sensitive to the heart rate. |
