A model of the systemic arterial bed showing ventricular-systemic arterial coupling.

A multielement model of the systemic arterial bed was implemented on a microcomputer and was used to simulate the transient response of the arterial circulation to a specific driving function: a linearly increasing left ventricular pressure. The elements (compliances and inductances) that simulate the aorta and its branches are determined by the characteristic impedances and time delays in the arterial system. The simulations of pressure and blood velocity signals found in a previous version of the model were improved by making the delays in the system nonuniform, with slow central and rapid peripheral wave speeds. This reduced the impedance into which the heart has to pump and increased the distal impedance, raising the peripheral diastolic pressures. When the reflection coefficient was decreased as the heart rate was increased, normal pressure and velocity signals could be maintained over a range of heart rates up to 150 min-1. Extrapolating this relationship to a heart rate of 200 min-1 indicated that the reflection coefficient could be zero at that heart rate, giving optimal power transmission through the arterial bed.