Ventricular performance in acute normovolemic anemia and effects of beta blockade

Abstract

Acute normovolemic anemia was produced in 18 dogs by isovolumic exchange with dextran. Mean hematocrit was reduced from 36.1 to 13.9% and cardiac output increased 91%. Heart rate, stroke volume, and left ventricular transmural end-diastolic pressure increased and residual fraction fell significantly. Systemic vascular resistance and end-systolic force fell, and both mean circumferential shortening rate and systolic ejection rate increased significantly during anemia. Improved performance of the left ventricle in anemia occurred due to the combined effects of increased myocardial contractility and a decrease in afterload. Beta adrenergic-blocking drugs were given to evaluate the contribution of the sympathetic nervous system to the cardiac responses in anemia. Nethalide was unsuited for this purpose because of its side effects. Cardiac output and heart rate decreased and systemic vascular resistance and transmural pressure increased after infusion of propranolol; these results do not necessarily indicate the magnitude of sympathetic activity in anemia, since a direct effect of this drug on the myocardium cannot be excluded.