Inotropic effect of carotid occlusion in intact anesthetized dog. Effects of dextran infusion and subsequent carotid occlusion on ventricular function.

Abstract

The effects of dextran infusion and subsequent bilateral carotid occlusion on left and right ventricular function were studied in 10 chloraloseurethane-anesthetized intact dogs. Volumes of both ventricles were measured by the thermodilution method during the control period, 10 min. after infusion of isotonic 6% dextran (40ml./Kg.), and after carotid occlusion. Dextran infusion increased cardiac output, stroke volume, and ventricular end-diastolic pressures (EDP) and volumes. Left ventricular end-diastolic volume (EDV) was greater than that on the right both before and after infusion. Bilateral carotid occlusion increased heart rate further, but a slight decrease in stroke volume resulted in no significant increase from infusion values in cardiac output. Left ventricular systolic pressure increased after occlusion, reflecting the increase in total systemic resistance; no significant change occurred in left or right ventricular end-diastolic or end-systolic volume. Right ventricular EDP decreased significantly and although left ventricular EDP also decreased the change was not significant. Plots of stroke work against left ventricular EDV after carotid occlusion lay significantly (P<0.005) above the regression line (r=0.75, P<0.01) for control and infusion points. Derived force-velocity relationships, expressed in terms of normalized mean circumferential shortening rate and peak ventricular force, showed an upward shift after carotid occlusion. We interpret these data as evidence of an increased inotropic effect of the myocardium following carotid occlusion.