Determinants of coronary flow and myocardial oxygen consumption

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Abstract
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.