EFFECTS OF ARTERIAL HYPOXEMIA AND HYPEROXIA ON OXYGEN AVAILABILITY FOR MYOCARDIAL METABOLISM - PATIENTS WITH AND WITHOUT CORONARY HEART DISEASE

Nineteen patients breathed different gas mixtures to induce arterial hypoxemia and hyperoxia. In 10 patients without heart disease, the level of coronary venous blood oxygen saturation fell during moderate arterial hypoxemia (O2 saturation 64 to 85 per cent) and rose during arterial blood hyperoxia. However, the coronary venous blood lactate/pyruvate concentration ratio ( L Pv) remained nearly constant, thereby providing evidence that the blood O2 changes did not reflect changes in O2 availability for myocardial metabolism. During severe arterial hypoxemia (O2 saturation 47 to 58 per cent), in 1 of 3 patients the myocardium produced lactate, which is a sign of supplementary anaerobic metabolism. In most of the 9 patients with coronary heart disease, the changes in coronary venous blood O2 saturation were similar to those in the control patients. However, exceptions occurred. In 3 patients with coronary heart disease, moderate arterial hypoxemia increased the L Pv, thus suggesting myocardial hypoxia. In 2 of these, the myocardium produced lactate (anaerobic metabolism). L Pv remained constant during hyperoxia; therefore, there is no evidence that the blood hyperoxia augmented myocardial O2 availability or relieved chronic myocardial hypoxia. © 1969.