Wave reflection and characteristic impedance in the conscious dog as influenced by adrenergic intervention

The combined measurement of aortic root pressure, flow and diameter permits determination of e.g. arterial compliance (C) and characteristic impedance (Zo). These systemic circulatory properties reflect the dynamic load to the left ventricle. Obviously, it is of clinical interest to study possible effects of cardiopharmacologic intervention on C and Zo. Therefore, the specific aims of this study are first to delineate the characteristics of the systemic circulation and second to analyze the influence of adrenergic agonists and blockers on C and Zo. We investigate these questions in the chronically instrumented dog by analyzing in particular effects of alpha- and beta-adrenergic drugs. We found that on average Zo amounts to 0.11 mmHg.s/ml, while medetomidine (by a rise of approximately 70%) causes the largest increase in Zo.