THE EFFECTS OF ACUTE HYPOXIA ON THE SYSTEMIC VENOUS AND ARTERIAL SYSTEMS AND ON MYOCARDIAL CONTRACTILE FORCE

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Abstract
Generalized systemic hypoxia produced an increase in venous return and a decrease in systemic blood volume (20%) in dogs studied during cardiopulmonary bypass. These effects interpreted as indicating systemic venoconstriction were abolished by aortic and carotid chemo-receptor stimulation. Hypoxia localized to the carotid arterial system produced an elevation in systemic vascular resistance, while a decline occurred when systemic hypoxia was produced while the carotid system was perfused with well oxygenated blood. Generalized hypoxia resulted in no mean change in systemic vascular resistance. A marked fall in systemic vascular resistance occurred shortly after reoxygenation only in animals with intact chemoreceptors. Myocardial contractile force increased to a similar degree during systemic hypoxia in the presence or absence of the adrenal glands, but decreased following chemoreceptor denervation or when the heart was perfused with poorly oxygenated blood while the carotid system was perfused with well oxygenated blood. These studies assessed the effects of hypoxia on isolated portions of the circulatory system and indicate the complex relationship between the direct and reflex effects of hypoxia.