Abstract
The present study was undertaken to explore the relationship between various doses of ouabain, myocardial contractility as reflected by the maximal rate of rise of left ventricular pressure and oxygen consumption, in the canine, nonfailing Starling heart-lung preparation modified to measure coronary flow. Concentrations of ouabain, previously found to be within “therapeutic” limits, as tested in the failing preparation, namely those attained 20 min and 30 min from the start of an infusion of ouabain (5μg/min), increased the maximal rate of rise of left ventricular pressure by an average of 13.4% and 24.2%, respectively, with no concomitant measurable increase in myocardial oxygen consumption. Changes in left ventricular work, left ventricular circumference, left ventricular end-diastolic and left atrial pressures were neither significant nor consistent. Concentrations of ouabain which induced ventricular tachycardia increased the maximal rate of rise of left ventricular pressure and myocardial oxygen consumption by an average of 205.2% and 81.4%, respectively. It may therefore be concluded from these results, that at constant aortic pressure and left ventricular dimensions an appropriate dose of ouabain induces in the isolated nonfailing heart an increase in contractility unaccompanied by a measurable increase in myocardial oxygen consumption.
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