Cardiovascular Control of and Responses to Vasoconstrictor Hormones During Hypoxia

摘要

These studies addressed the role of certain factors on the ability to maintain blood pressure (BP), cardiac output (CO) and O2 delivery (O(2)del) during hemorrhage in the conscious goat. We studied the effects of oxygen content of inspired air, the presence of the spleen, roles of arginine vasopressin (AVP), the renin- angiotensin system, and the presence of estrogen. We observed 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% FIO(2) , reduced mean arterial BP by approximately 25, 15, and 5 mmHg respectively. Improved maintenance of BP during hyperoxia was achieved by an earlier rise in systemic vascular resistance, and O(2) consumption was similar in all experiments following hemorrhage. Presence of the spleen did not affect the magnitude of drop in BP, O(2)del, nor hormonal responses to the hemorrhage. In other experiments, i.v. infusions of AVP in goats breathing 11% FIO(2) increased the arterial O(2) concentration, but the AVP-induced decrease in cardiac output prevented an improvement in O(2)del. Neither hypoxia nor the rate of AVP infusion affected whole body AVP clearance. Lastly, we observed that estrogen administration to gonadectomized female or male goats lowered the hypotensive threshold during hemorrhage because of a reduced ability to maintain CO.