Circulatory and metabolic effects of oxygen in myocardial infarction

The circulatory and metabolic effects of inhalation of oxygen in high concentration were investigated in 50 patients with acute myocardial infarction. The heart rate, arterial blood pressure, cardiac out-put, blood gas tensions, pH, and lactate and pyruvate levels were measured. In general, oxygen inhalation produced a fall in cardiac output and stroke volume and a rise in blood pressure and systemic vascular resistance. In a small number of patients with very low cardiac out-puts there was a rise in output. A substantial rise in arterial oxygen tension was obtained even in patients with low initial values. The raised arterial blood lactate levels which were frequently present were reduced after oxygen. The therapeutic implications of these effects are discussed.