Influence of Carotid Baroreceptors and Vasoactive Drugs on Systemic Vascular Volume and Venous Distensibility

Abstract

Changes in systemic vascular volume, in venous return, and in the distensibility of the venous system were studied in an experimental canine preparation. The use of an extracorporeal circulation permitted complete exclusion of the heart and lungs and allowed continuous measurement of alterations of intravascular blood volume and of venous return to the oxygenator. Brief occlusion of the venous outflow line permitted the inscription of venous pressure-volume curves. Hypotension in the isolated carotid sinuses, the administration of catecholamines or of acetylcholine resulted in venoconstriction, evidenced by a decrease in vascular volume, an increase in venous return, and flattening of the venous occlusiou curves. Conversely, carotid sinus hypertension or the administration of trimethaphan produced venodilatation, a decline in venous return, and an increase in vascular volume. The significance of these observations in the regulation of cardiac output is discussed.