A simple method for Emax evaluation: In vitro results

E(max) is an important parameter to evaluate the state of the heart and of its contractile capability. Its determination is not easy and rather inaccurate: However, it can be clinically relevant during mechanical and/or pharmacological heart assistance as it can suggest how to modify pharmacological therapy or the control strategy of the device. Aim of this study is to develop a method based on ventricular energetics to evaluate E(max). If arterial elastance line slope is modified, for example by a slight peripheral resistance increase, E(max) (assuming that it is constant) can be evaluated computing the energy transferred to the arterial elastance before and after the change. The corresponding equation contains known or easily computable variables and the difference delta between end diastolic volume and ventricular rest volume. If the ratio of deltas before and after the disturbance is near to 1, the equation returns a fair estimation of E(max). The method was tested in vitro, in different circulatory conditions, using an open loop numerical model of the circulation built out of a variable elastance model of the ventricle connected to a modified windkessel representing the systemic arterial tree. The results obtained in in vitro experiments suggest clinically testing this method.