The fractional rate of change of ventricular power during isovolumic contraction. Derivation of haemodynamic terms and studies in dogs.
Power and the rate of change of power generated by the ventricle during isovolumic contraction can be calculated on the basis of the energy expended upon compression of the blood within the ventricle during this phase of systole. The ratio of the instantaneous rate of change of power, normalized to instantaneous power, appears to be an expression of particular physiological significance and practical value. This ratio, termed the isovolumic fractional rate of change of ventricular power, describes the capability of the ventricle to sustain an acceleration of energy production relative to instantaneous rates of energy production during isovolumic contraction. In dogs, the fractional rate of change of power changed insignificantly with changes of the preload and afterload; yet its magnitude varied prominently with drug-induced alterations of the contractile state. Although the isovolumic fractional rate of change of power takes a form that in some ways is similar to some previously derived indices of performance, it is independent of assumptions of ventricular geometry, fibre orientation, symmetry of contraction, or elasticity of muscle fibres. The isovolumic fractional rate of change of power is both meaningful and theoretically valid. For these reasons, it appears preferable to empirically-derived indices of performance or indices based upon assumptions which are approximations.
D000818:Animals; D002306:Cardiac Volume; D004285:Dogs; D004734:Energy Metabolism; D006321:Heart / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D011433:Propranolol / Q000494:pharmacology; D013268:Stimulation, Chemical; D016276:Ventricular Function
D011433:Propranolol; D007545:Isoproterenol