Effect of cardiac rhythm on vena caval blood flows

Abstract

Cannulating electromagnetic flow probes were inserted into superior and inferior venae cavae of anesthetized mongrel dogs. The relationship between instantaneous venous blood flow and right atrial and ventricular activities were studied during both normal and various abnormal cardiac rhythms. In particular, the relationship of increased bloodflow recorded during the simultaneous atrial relaxation and ventricular contraction was assessed. When atrial relaxationwasseparatedfromventricular contraction, increased atrial inflow was still recorded during isolated atrial relaxation but not during an isolated ventricular contraction. When atrial and ventricular systoles occurred simultaneously, marked regurgitation of blood from the atrium into the venous system was observed. It is concluded that not only atrial contraction but also atrial relaxation provide important functions for the ventricle. Atrial relaxation is associated with a rapid inflow of blood from the venae cavae into the atrium. This provides a reservoir of blood immediately available for rapid filling of the ventricle at the beginning of its diastole.