Numeric modeling of the cardiovascular system with a left ventricular assist device.

A numeric model consisting of a lump-parameter cardiovascular system (CVS) model and a model for the Cleveland Clinic Implantable Ventricular Assist System (IVAS), a nonpulsatile rotary pump designed to augment the failing left ventricle, are described in this paper. The purposes of this study were to 1) observe the hemodynamic interactions between CVS and IVAS under various physiologic and pathophysiologic conditions running at different speeds; and 2) allow testing and optimization of various IVAS control algorithms. An existing numeric model of CVS (24 coupled differential equations, representing all cardiac chambers and systemic and pulmonary vasculature) was modified to add the IVAS pump as an auxiliary chamber between the left ventricle and aorta with pressure-flow-speed characteristics derived from in vitro testing. Simulations were conducted for ventricles with normal and abnormal systolic and diastolic dysfunction at different exercise levels with the pump running at various speeds. Computer simulations show that 1) numeric modeling is useful for predicting hemodynamic response of CVS to IVAS in various circumstances; 2) IVAS results in normalization of cardiac output, especially in failing hearts, although with reduced pulse pressure; and 3) various control algorithms allowing adaptation of IVAS to physiologic demands of CVS could be developed based on the simulation study.