Hydraulic input impedance to aorta and pulmonary artery in dogs

Pressure-flow relationships were studied at the root of the aorta and the pulmonary artery in 18 dogs. The hydraulic input impedance to the vascular bed was calculated as a complex ratio of the corresponding pressure and flow harmonics. Results indicate: a) The predominant features of the load against which the heart is pumping consists of an impedance with a magnitude that initially decreases rapidly with frequency and then increases gradually with frequency. In general, pressure tends to lag behind flow for all harmonics. b) The input impedance versus frequency patterns provided a logical basis for choosing various simple electrical networks which can be used to characterize in a compact manner the general features of the hydraulic load presented to the ventricles. c) The hazards of using such simple networks to define the physical properties of the vascular system are pointed out. Submitted on July 5, 1962 Submitted on July 30, 1962