Acute effects of arterio-venous shunt on cardiovascular hemodynamics in rat.

The cardiovascular effects of an acute high cardiac output state (Acute HCO) were determined in rats 24 h after opening an abdominal aorta-caval shunt equal to 50% of total cardiac output (CO). Heart rate (HR), left ventricular peak (LVP), end diastolic (LVEDP), and arterial (AP) pressures, CO, stroke volume (SV), total systemic and regional vascular resistance (VR), regional blood flow (BF) (radioactive microspheres), and tissue fluid content data were collected. In Acute HCO, AP and LVP were reduced while LVEDP was elevated, total CO was increased and total VR was decreased while systemic CO and VR were unchanged. In Acute HCO, HR did not change significantly and SV was significantly increased. Lung water in Acute HCO was significantly greater than control. Regional BF changes in Acute HCO include skeletal muscle reflex vasoconstriction and splanchnic and cerebral dilation. The results in conjunction with previous data on chronic HCO indicate that in the rat (1) increased lung water which is absent after cardiovascular compensation is an acute result of HCO, and (2) the acute phase of cardiac compensation to HCO occurs in the absence of a tachycardia response.