Determinants of coronary flow and myocardial oxygen consumption

¹ Cardiovascular Department, Medical Research Institute, Michael Reese Hospital and Medical Center, Chicago, Illinois

The effect of altering hemodynamic parameters and blood milieu on myocardial oxygen extraction (O₂E) was observed in an improved preparation of the anesthetized, open-chested dog. O₂E remains at or near its high level for at least 40 min despite shifts in pH and cardiac input and sustained aortic compression. Aortic compression at constant cardiac input is associated with a moderate O₂E decrease. Alternate aortic compression and release accompanied by induced shifts in pH and pCO₂ caused an earlier and accelerated O₂E decline. Coronary flow (CF) ordinarily is at a minimum for a given cardiac effort and rises when O₂E declines. The O₂E fall and CF increase are considered evidence of loss of coronary vascular tone. Despite shifts between CF and O₂E, myocardial O₂ consumption (O₂C) remains closely associated with the cardiac effort index (mean aortic pressure x heart rate—HR·BP). Shifts in cardiac input, pH, and/or pCO₂ have minimal effects on this O₂C/HR·BP relationship. The significance of HR·BP as an energy utilization index is discussed.

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