A simple method for E-max trend evaluation: in vitro and in vivo results

The aim of this study is the evaluation of end systolic ventricular elastan ce trend (as a measure of heart contractility) by hemodynamic variables ava ilable in intensive care units or during heart surgery: heart rate, cardiac output, left atrial, mean and diastolic arterial pressure. Its basic assum ption is the description of ejection as the interaction between variable le ft ventricular and arterial compliances (reciprocal of the corresponding el astances) connected in parallel. As pressure is the same in each compliance at systole beginning and ending, ventricular elastance can be estimated by assuming that energy variation is the same on both compliances. The algori thm has been tested on a numerical simulator of the circulatory system and on six sheep at basal conditions and during drug infusion. Correlation func tion in numerical simulation, between true and computed ventricular elastan ce (range 0.45 divided by 5 mm Hg-cm(-3)), yields 0.985. In vivo comparison between computed ventricular elastance trend and ventricular dp/dt trend y ields a correlation function ranging between 0.87 and 0.99. The result of the algorithm cannot be assumed to be E-max value. However, i t can be considered a contractility index as it closely follows any change in dp/dt. It can be computed by simple calculations and needs no variables of her than those usually measured in intensive care. It allows the extrapo lation of useful information for evaluating the trend in heart contractilit y and for setting up a control strategy for mechanical or pharmacological a ssistance during heart recovery.