Peripheral circulatory control of preload-afterload mismatch with angiotensin in dogs

To determine whether changes in the venous circulation were responsible for preload-afterload mismatch with angiotensin, we examined the changes in the heart and the peripheral circulation in six splenectomized dogs after ganglion blockade during an angiotensin infusion to increase mean aortic pressure 25 and then 50%. The peripheral circulation was evaluated by measuring mean circulatory filling pressure (MCFP), arterial compliance, and venous compliance. A 25% increase in mean aortic pressure increased MCFP from 6.2 ± 0.3 to 7.6 ± 0.3 mmHg (P < 0.001) but did not change cardiac output, heart rate, or stroke volume. Systemic vascular resistance increased (P < 0.01) from 0.50 ± 0.02 to 0.59 ± 0.03 mmHg·min·kg·ml^-1. Arterial and venous compliances decreased (P < 0.01) from 0.08 ± 0.03 to 0.06 ± 0.03 ml·mmHg^-1·kg^-1 and from 2.1 ± 0.1 to 1.6 ± 0.1 ml·mmHg^-1·kg^-1, respectively. A 50% elevation in mean aortic pressure increased MCFP from 7.1 ± 0.4 to 9.5 ± 0.9 mmHg (P < 0.001) but did not change heart rate. At this level of aortic pressure, cardiac output and stroke volume decreased (P < 0.01) 12 and 19%, respectively, whereas systemic vascular resistance increased (P < 0.001) from 0.48 ± 0.03 to 0.83 ± 0.05 mmHg·min·kg·ml^-1. Arterial and venous compliances decreased (P < 0.01) from 0.08 ± 0.01 to 0.05 ± 0.01 ml·mmHg^-1·kg^-1 and from 2.1 ± 0.1 to 1.4 ± 0.1 ml·mmHg^-1·kg^-1, respectively. Total blood volume was unchanged but central blood volume increased (P < 0.001) 25% with each infusion. The decrease in cardiac output with high doses of angiotensin resulted from inadequate venous return and limited volume mobilization.