Myocardial oxygen consumption:: The quest for its determinants and some clinical fallout (Reprinted from the American Journal of Cardiology, September 1968)

The factors that control the consumption of oxygen and utilization of energy by the heart have been of interest to cardiovascular physiologists and clinicians for many years. The determinants of myocardial oxygen consumption (MVO2) have warranted this careful consideration since, in the presence of steady state conditions and with the obligatory aerobic nature of myocardial metabolism MVO2 serves as a measure of the total energy utilization of the heart. Therefore, since utilization of high energy phosphates, which constitute the immediate energy source for contraction, is not readily determined directly, advantage is taken of the close correlation between energy utilization and MVO2, and the latter is measured experimentally. Further, under clinical conditions that place a restraint on coronary blood flow and, hence, on the availability of oxygen to the myocardium, factors that alter MVO2 become a primary consideration. A major advance in our understanding of the determinants of MVO2 has come from an appreciation that cardiac muscle is subject to the same general principles of control and analysis as is skeletal muscle. Thus, the same factors that govern the conversion of chemical energy into mechanical work in skeletal muscle are important considerations in dealing with heart muscle. In the present discussion the development of an integra integrative concept of the determination of MVO2 will be reviewed and its relation to our present knowledge of muscle mechanics will be assessed briefly. Such a synthesis may offer insight into some of the apparent discrepancies and inconsistencies with which the literature on the subject abounds and may provide a more rational framework for understanding the dynamic control of MVO2 in both physiologic and pathologic states.