Cardiovascular Control of and Responses to Vasoconstrictor Hormones During Hypoxia.

Abstract : The purpose of these studies is to determine factors affecting blood pressure (BP) maintenance during hemorrhage and the consequences on O2 delivery (O2del). The scope covers the cardiovascular, oxygen delivery, and hormonal responses to hemorrhage while breathing hyperoxic, normoxic and hypoxic air mixtures, in conscious goats. Additionally, the role of the hormonal responses, particularly vasopressin (AVP) and angiotensin II, on the cardiovascular and O2del responses is being investigated. We have shown that a controlled hemorrhage at 0.5 ml/kg/min for 30 min conducted in the same goats while exposed to either 11, 21, and 100% FIO2, reduced mean arterial BP by approximately 25, 15, and 5 mmHg respectively. Improved maintenance of BP during hyperoxia was achieved, in part, by an earlier rise in systemic vascular resistance, and O2 consumption was similar in all experiments following hemorrhage. Presence of the spleen did not affect the magnitude of drop in BP, O2del, nor hormonal responses to the hemorrhage during normoxic conditions. Other experiments involved responses to i.v. infusions of AVP during 11 or 21% FIO2. AVP increased the arterial O2 concentration during hypoxia as expected, but the AVP-induced decrease in cardiac output prevented an improvement in O2del. Neither hypoxia nor the rate of AVP infusion affected whole body AVP clearance.