Intraventricular pressure drop and aortic blood acceleration as indices of cardiac inotropy: a comparison with the first derivative of aortic pressure based on computer fluid dynamics.

This paper presents a computational approach to ventricular fluid mechanics to evaluate three inotropic indices of early ejection: the intraventricular pressure drop (deltap). the first derivative of aortic flow rate (df/dt) and the first derivative of aortic pressure dp/dt. dp/dt is one of the most frequently used indices for assessing myocardial inotropy. Deltap and df/dt are characteristic of inertia driven flows and reflect the impulsive nature of the flow inside the ventricle during the ejection phase. The study is based on an axisymmetric fluid dynamics model of the left ventricle, developed according to the finite element approach. The fluid cavity is bounded by a shell containing two sets of counter-rotating contractile fibres. Two simulation sets were performed: the former to investigate the sensitivity of deltap and df/dt peaks (deltap(max) and df/dt(max)) with respect to changes in the inotropic state of the fibre. The latter allows the evaluation of the dependency of deltap(max) and df/dt(max) on afterload by means of two supravalvular stenoses of 50% and 70%. The model simulates the inertial features of ventricle behaviour. The calculated values of the indices investigated are in close agreement with those reported in the literature. The sensitivities of deltap(max) df/dt(max) and dp/dt(max) are calculated for the two simulation sets. Data are normalised with respect to the maximum values reached in the simulation set. The comparison indicates that deltap(max) has a greater sensitivity (3.4 vs. 3.1 ) and a more linear pattern than dp/dt(max) for changes in the inotropic state of the fibre. df/dt(max), shows a sensitivity close to dp/dt(max). Results confirm that the afterload does not affect dp/dt(max), in accordance with experimental observations, while deltap(max) and, to a major degree, df/dt(max) decrease when the afterload is increased.