Effects of oxygen on myocardial blood flow and metabolism

The effects of inhalation of oxygen on myocardial blood flow and metabolism were studied in 10 patients with rheumatic or congenital heart disease. Myocardial blood flow was measured by injection of 133Xe into the left ventricle and sampling from the coronary sinus and aorta. Lactate, pyruvate, and oxygen levels were estimated in arterial and coronary venous blood. Intra-arterial pressures, cardiac output, and heart rate were also measured. After oxygen there was a significant fall in heart rate and myocardial blood flow. There were no significant changes in mean arterial blood pressure or cardiac output. Myocardial oxygen uptake was not altered significantly. The effect on lactate extraction and lactate/pyruvate ratios was variable. The results indicate that inhalation of high concentrations of oxygen does not necessarily increase myocardial oxygen availability.