Interaction of heart and arterial system

Abstract

We have studied the interrelation of left ventricle and arterial system in the anesthetized open-thorax cat. The ventricle was characterized by its pump function graph, relating mean ventricular pressure ($\bar P_{lv}$) and mean aortic flow ($\bar F$). The pump function graph was determined by means of an artificial periphery and on a beat-to-beat basis. The periphery was characterized by relating mean aortic pressure ($\bar P_{ao}$) and mean flow. Mean aortic and mean left ventricular pressure could be related over a wide range of values by a proportionality factor$\bar P_{ao} = a \cdot \bar P_{lv}$. In a series of five separate experiments a value of a=1.72±0.14 (mean±SD) was found. This simplified relation allows direct comparison of apparent source resistance (i.e., slope of pump function graph), (R_s), and peripheral resistance (R_p). It was also found experimentally that total external power ($\bar \dot w$) could be calculated from mean aortic pressure and mean flow as well as from mean left ventricular pressure and mean flow (thus from the pump function graph) by$\bar \dot w = c \cdot \bar P_{ao} \cdot \bar F = c \cdot a \cdot \bar P_{lv} \cdot \bar F$. The value of c=1.16±0.12 (mean±SD, n=4). Maximum external power was predicted for$R_p /R_s = \bar P_{ao} /\bar P_{lv} = a$. In six different cats R_p/R_s ratio in the working point (i.e., mean left ventricular pressure and mean flow when the normal periphery loaded the heart) was found to be R_p/R_s=2.63±0.92. This value could not be shown to differ from that in the point where maximal external power was found, i.e., R_p/R_s=1.81±0.08 (n=6).