The effect of altering hemodynamic parameters and blood milieu on myocardial oxygen extraction (O 2 E) was observed in an improved preparation of the anesthetized, open-chested dog. O 2 E 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 O 2 E decrease. Alternate aortic compression and release accompanied by induced shifts in pH and pCO 2 caused an earlier and accelerated O 2 E decline. Coronary flow (CF) ordinarily is at a minimum for a given cardiac effort and rises when O 2 E declines. The O 2 E fall and CF increase are considered evidence of loss of coronary vascular tone. Despite shifts between CF and O 2 E, myocardial O 2 consumption (O 2 C) remains closely associated with the cardiac effort index (mean aortic pressure x heart rate—HR·BP). Shifts in cardiac input, pH, and/or pCO 2 have minimal effects on this O 2 C/HR·BP relationship. The significance of HR·BP as an energy utilization index is discussed.
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Feinberg et al. (1962) studied this question.