Heart rate as a determinant of cardiac output in dogs with arteriovenous fistula

Abstract

The importance of heart rate in the control of cardiac output under conditions of a high level of venous return was studied in a series of 17 anesthetized open chest dogs with the atrioventricular bundle cut. The results show that high heart rates do not increase cardiac output under conditions of normal venous return. On the other hand, when venous return is markedly increased above normal by opening large arteriovenous fistulas, maximal cardiac output is achieved only at very high heart rates. As venous return increases, the heart rates at which maximal values of cardiac output are obtained are progressively increased. Norepinephrine or sympathetic stimulation further elevates the heart rate required for maximal cardiac output. These observations help to explain why tachycardia and the other cardiostimulant actions of the sympathetic nervous system play an important role in the regulation of cardiac output.