Hemodynamics in Hemorrhage: Influences of Sympathetic Nerves and Pentobarbital Anesthesia

Summary

In the unanesthetized splenectomized dogs, hemorrhage causes 1.5% decrease in cardiac output for each 1.0% reduction in blood volume. The posthemorrhage decreases in arterial pressure and cardiac output in these unanesthetized dogs with sympathetics intact are less than those seen in the unanesthetized sympathectomized dogs, but the pressure-output relations are essentially the same in these two groups. Therefore in the unanesthetized state, the sympathetic system aids in the maintenance of the circulation primarily by its cardiac influence with little action on the overall vascular resistance. In contrast, with the use of pentobarbital anesthesia, hemorrhage cannot further increase the discharge of the cardiac sympathetics and the major sympathetic response is to cause constriction of the resistance vessels.