EFFECTS OF HYPERBARIC HYPEROXIA ON CARDIAC AND REGIONAL HEMODYNAMICS IN CONSCIOUS DOGS

Background: Although evidence of systemic vasoconstriction has been re ported both in animal models and in humans, the regional hemodynamic e ffects of hyperbaric hyperoxia have not been well characterized. Metho ds: In the present study, we report the effects of hyperoxia (normobar ic and hyperbaric) on simultaneous measurements of cardiac and regiona l hemodynamics in the chronically instrumented conscious dog. Results: Hyperbaric hyperoxia (202 kPa) produced significant decreases in hear t rate (12%) and cardiac output (20%) and a significant increase in sy stemic vascular resistance (30%). Carotid artery blood flow decreased significantly (18%) whereas coronary, hepatic, renal and mesenteric fl ows remained unchanged. Conclusions: Our data show that the hyperoxic vasoconstriction is limited to the cerebral and peripheral vascular be ds. Additionally, blood flow to major organs is well preserved in the face of hyperoxia-induced decreases in cardiac output. Consequently, w e postulate that a redistribution of blood flow from peripheral vascul ar beds (e.g., skin, muscle, bone) to major organs occurs during hyper baric hyperoxia.