INTRAVENTRICULAR PRESSURE-DROP AND AORTIC BLOOD ACCELERATION AS INDEXES 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 mech anics to evaluate three inotropic indices of early ejection: the intra ventricular pressure drop (Delta p), the first derivative of aortic fl ow 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. Delta p and df/dt are characteristic of inertia driven flow s and reflect the impulsive nature of the flow inside the ventricle du ring the ejection phase. The study is based on an axisymmetric fluid d ynamics model of the left ventricle, developed according to the finite element approach. The fluid cavity is bounded by a shell containing t wo sets of counter-rotating contractile fibres. Two simulation sets we re performed: the former to investigate the sensitivity of Delta p and df/dt peaks (Delta p(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 Delta p(max) and df/dt(max) on afterload by means of two supravalvular stenoses of 50% and 70%. The model simulates the in ertial features of ventricle behaviour. The calculated values of the i ndices investigated are in close agreement with those reported in the literature. The sensitivities of Delta p(max), df/dt(max) and dp/dt(ma x) are calculated for the two simulation sets. Data are normalised wit h respect to the maximum values reached in the simulation set. The com parison indicates that Delta p(max) has a greater sensitivity (3.4 vs. 3.1) and a more linear pattern than dp/dt(max) for changes in the ino tropic 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 Delta p(max) an d, to a major degree, df/dt(max) decrease when the afterload is increa sed. (C) 1998 IPEM. Published by Elsevier Science Ltd. All rights rese rved.