Abstract
Blood flow of the superior (SVC) and inferior venae cavae (IVC) was simultaneously and separately measured with two cannulating type electromagnetic blood flow probes inserted into the SVC and IVC of thirty two dogs during hypotensive and low cardiac output states in hemorrhagic shock and cardiogenic shock. Blood flow ratio of the IVC to total venous return was expressed by IVCF/CO (%). It was 66.3% in normal condition, but was decreased to 54.3% in hemorrhagic shock. In four cardiogenic shock models, however, IVCF/CO changed little from the control to the initial phase of shock state. At least in part, the marked decrease of venous return from the IVC region in hemorrhagic shock was considered due to the increase of sympathetic nerve activity in that region mediated by baroreceptors in the high pressure system. The unchanged blood flow ratio of the SVC and IVC in cardiogenic shock was assumed that the high atrial or high ventricular endodiastolic pressure was an inhibitory factor of the sympathetic nerve activity by activating the stretch receptors existing in the low pressure system including left ventricle. This hypothesis was proved by the experiments in which the renal vascular resistance was suppressed by stretch of the left atrium by either extraatrial mechanical traction or intraatrial balloon inflation in hemorrhagic shock or intracardiac decompression during cardiopulmonary bypass.
