Myocardial coefficient of oxygen utilization.

THE COEFFICIENT of oxygen utilization is defined as the arteriovenous difference in oxygen concentration divided by the concentration of oxygen in the arterial blood. Multiplication of the ratio by 100 converts the coefficient into the per cent of arterial oxygen which is removed by the tissue. The term "oxygen extraction ratio" is frequently used as a synonym. Conflicting reports have appeared in the literature concerning the relationship between the arterial oxygen content and the myocardial coefficient of oxygen utilization. Feinberg et al. have reported a positive relationship, while Hackel and co-workers found a consistent inverse relationship between arterial oxygen content and the coefficient of oxygen utilization during hypoxemia. Both groups used dogs as the experimental animal, but different methods of measuring coronary flow were employed. In the normal range of arterial oxygen values no correlation appeared to exist. Some investigators, however, have been impressed with the constancy of the coefficient under certain experimental conditions and have used this value as an index of coronary flow. Since the published reports disagree on the relationship of arterial oxygen content to the coefficient of utilization, it may be unwise to use the latter value as an index of coronary flow. In view of the discrepancies found in the literature, a re-examination of the pertinent factors, particularly coronary flow, blood oxygen values, and estimated myocardial oxygen consumption, has been undertaken.