Effect of cardiac rhythm on vena caval blood flows.

PINKERSON, ALAN I;., MYRON H. LURIA, AND EDWARD D. FREE, Effect of cardim rhythm on vena caval blood j?ows. Am. J, Physiol. 2 I o(3) : 505-508. I g66.-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 atria1 and ventricular activities was studied during both normal and various abnormal cardiac rhythms. In particular, the relationship of increased blood flow recorded during the simultaneous atria1 relaxation and ventricular contraction was assessed. When atria1 relaxation was separated from ventricular contraction, increased atria1 inflow was still recorded during isolated atria1 relaxation but not during an isolated ventricular contraction. When atria1 and ventricular systoles occurred simultaneously, marked regurgitation of blood from the atrium into the venous system was observed. It is concluded that not only atria1 contraction but also atria1 relaxation provide important functions for the ventricle. Atria1 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.