Mechanical Efficiency in Conscious Dogs
نویسندگان
چکیده
Background We studied the effect of exercise (7.2 to 8.0 km/h) on the efficiency of the conversion of metabolic energy to external work or stroke work (SW) by the left ventricle (LV). Methods and Results Energy use was calculated from LV myocardial oxygen consumption per beat (MVo2). LV volume was calculated from orthogonal dimensions and coronary flow measured with ultrasonic flow probes. The total mechanical energy of the LV was calculated as the pressure-volume area (PVA). At rest, the MVo2-PVA point fell on the MVo2-PVA relation determined by steady-state changes in arterial pressure produced by graded infusions of phenylephrine. Exercise increased the slope (Ees) of LV end-systolic pressure-volume (PV) relation by 29%. During exercise, the MVo2-PVA point shifted to the right only slightly above the control MVo2-PVA relation by 0.007±0.005 mL 02 beat` * 100 g LV`1. Despite the increase in ventricular contractility with exercise, the
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