Parameter Estimation of a Simple Model of the Left Ventricle and of the Systemic Vascular Bed, with Particular Attention to the Physical Meaning of the Left Ventricular Parameters

The goal of this study is to estimate the values of the parameters of a simple electrical model of the cardiovascular system and to evaluate whether some physical interpretation can be given to the left ventricular parameters. In this model, the left ventricle is represented by a time varying capacitance C(t) analogous to the instantaneous left ventricular pressure/volume ratio, and the systemic vascular bed by two capacitances (Cl, C2), one inductance (L) and one resistance (r). The parameter values are computed from only two measurements: the instantaneous pressurepao(t) and the mean flow Q¿ao at the root of the aorta during one beat. First, r is calculated as the ratio between P¿ao and Q¿ao. Thereafter, Jazwinski´s nonlinear filter is used to compute L, C1, C2 from the diastolic part of pao (t), and C(t) from the systolic part of pao(t). The shape of ê(t), i.e., 1/¿(t) during one beat, estimated from our experiments on dogs, varies strongly after isoproterenol injection (increase in myocardial contactility) but remains unchanged after neosynephrine and amyl nitrite administration (changes in peripheral vascular resistance). These results suggest that the estimated ê(t), like the actual pressure/volume ratio measured by Suga is related to the contractile state of the left ventricle.