Principle of a noninvasive method of measuring Max(dP/dt) of the left ventricle: theory and experiments.

In early systole, before the effects of reflected waves from the periphery become significant, the following equation applies: PA - PO = rho cu (1) where PA and PO are the instantaneous and end-diastolic pressures in the ascending aorta, rho the density of blood, c the velocity of the pulse wave in the aorta, and u the velocity of blood. Differentiation of Eq. (1) with respect to time t yields: dPA/dt = rho c(du/dt) (2) If there is no aortic stenosis, and if the pressure gradient due to the inertia of the blood during acceleration is neglected, the left ventricular pressure P is nearly equal to PA during the ejection period. Since both dP/dt and dPA/dt take their maximum values at times close to the time of aortic valve opening, the following equation applies: Max(dP/dt) not equal to Max(dPA/dt) (3) where Max signifies the maximum value of a derivative. Equation (2) reduces to: Max(dPA/dt) = rho c Max(du/dt) (4) Substitution of Eq. (4) into Eq. (3) yields: Max(dP/dt) not equal to rho c Max(du/dt) (5) Experiments were performed on seven dogs. Max(dP/dt), Max(du/dt), and c were measured during volume loading, pressure loading and unloading, and before and after administration of positive and negative inotropic agents. There was a good linear correlation (Y = 1.01X-2, r = 0.97) between Max(dP/dt) and rho c Max(du/dt). Therefore, Eq. (5) is a universal equation which holds, irrespective of the dogs and interventions employed to change the hemodynamic state.(ABSTRACT TRUNCATED AT 250 WORDS)