IDENTIFICATION OF LEFT VENTICULAR MODEL PARAMETERS Herman

Simulations with a model of left ventricular pressure generation consisting of time varying Elastance, Resistance, Series-Elastance and Deactivation were fitted to pressure curves measured in the isolated rabbit ventricle. For constant ejection flows a fit with a RMS error of 2.78 mmHg was obtained provided that deactivation was actually incorporated in the model. Deactivation was assumed to depend linearly on end ejection pressure. Resistance was found t o be independent of volume. INTRODUCTION It has been shown that for constant ejection flow the left ventricle can be described by an Elastance E t ) [l], a Resistance R(t) [2], a Series-Elastance Es(t) [3\ and a Deactivation [4], interpreted as a time varying parallel elastance Ed(t). The time variances in the parameters appear to obey: Thus a common time function f(t) is involved, which corresponds to the time course of isovolumic pressure. The validity of this model has been derived from different and restricting experiments specifically adapted to measurement of the respective parameters. In this paper we address the question whether the complete model can accurately and non-redundantly describe ventricular pressure before, during and after constant flow ejection. Thus model simulations are fitted to experimental pressure curves, and model parameters are collectively identified. THEORY The abovef ive lement model is sinulakd.by numerically solving the finite difference equation Ve( t )-Ve( t -A t ) +re + rs V e ( t ) . A t = y 7s [V(t)-Vd].At P r (1) Where V(t) is ventricular volume, Ve(t) the volume of the elastance compartment and At is the time difference used. Vd is residual volume. Ftesistance p is admittedly volume dependent: where t m is time of end ejection. Ventricular pressure is given by d t l V ) ?sy,.f(t). [V(t)-Ve(t) -vd] (3) At end ejection Elastance is deactivated by a factor a (51) which has been shown [4] to be equal to