Effects of Acute Valvular Regurgitation on the Oxygen Consumption of the Canine Heart

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Abstract
The effects on myocardial oxygen consumption and mechanics of acute, simulated aortic and mitral regurgitation were studied in open-chest, anesthetized dogs to determine how changes in the mechanical performance of the ventricle alter oxygen consumption. When regurgitation was induced acutely with effective stroke volume (total stroke volume less regurgitant volume) and heart rate held constant, left ventricular end-diastolic volume, total stroke volume, the ejection fraction, left ventricular wall tension, and the extent of shortening of the contractile element and the circumferential fibers all increased. With volumes of regurgitation approaching effective systemic blood flow, oxygen consumption increased only moderately, despite the increases in tension and shortening. When valvular regurgitation was induced while peak ventricular wall tension was held relatively constant, stroke volume doubled and the extent of both contractile element and circumferential fiber shortening increased. Contractile element work in generating tension was unchanged; that which led to fiber shortening increased substantially. Myocardial oxygen consumption did not increase significantly. Thus, marked increases in the efficiency of the contractile elements and myocardial fibers occurred. The low energy cost per unit of work expended in shortening as opposed to that used for tension development therefore allows the excess stroke volume of valvular regurgitation to be maintained at only a small added oxygen cost to the ventricle.