Effective length of the arterial circulation determined in the dog by aid of a model of the systemic input impedance

By ´effective length´ it is meant that if the systemic arterial tree is represented by an equivalent tube with one terminal reflection site, the effective length is the distance from the aortic valve to this site. The purpose of the present study was to develop a reliable method to determine this distance. Aortic pressure and flow and aortic radius were measured in seven dogs during steady state. The arterial system was represented by a uniform elastic and frictionless equivalent tube loaded with a complex load. Load parameter and tube inertance and compliance were estimated by fitting pulsatile aortic flow with flow predicted by the model using pressure as input. The fit was good, and parameter estimates compared well to values reported in the literature. The tube length was calculated from estimates of the inertance and the inner aortic radius. The results confirmed that the quarter-wave formula traditionally used significantly overestimates the distance to the effective reflection site.