Hemodynamic Responses to Oxygen Breathing and the Effect of Pharmacological Blockade

Breathing of 100% oxygen at 1 atmosphere for 20 min in healthy subjects produces consistent cardiac depression and vasoconstriction. These adverse hemodynamic effects abolish the expected rise in general and regional oxygen transport. Pharmacological blockade of various types proved phenoxy‐benzamine and atropine to be the only agents effective in preventing cardiac depression. An increase of total oxygen transport thereby occurred. In contrast vasoconstriction and blood pressure rise followed oxygen breathing irrespective of the type of pharmacological blockade applied. Consequently regional oxygen transport remained unaltered. The study provides evidence that cardiac depression and vasoconstriction as precipitated by oxygen breathing are separate and independent effects and that both are mediated via metabolic pathways.