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 S ystem (IVAS), a nonpulsatile rotary pump designed to augment the failing le ft ventricle, are described in this paper. The purposes of this study were to 1) observe the hemodynamic interactions between CVS and IVAS under vario us 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, repres enting all cardiac chambers and systemic and pulmonary vasculature) was mod ified to add the IVAS pump as an auxiliary chamber between the left ventric le and aorta with pressure-flow-speed characteristics derived from in vitro testing. Simulations were conducted for ventricles with normal and abnorma l systolic and diastolic dysfunction at different exercise levels with the pump running at various speeds. Computer simulations show that 1) numeric m odeling is useful for predicting hemodynamic response of CVS to IVAS in var ious circumstances; 2) IVAS results in normalization of cardiac output, esp ecially in failing hearts, although with reduced pulse pressure; and 3) var ious control algorithms allowing adaptation of IVAS to physiologic demands of CVS could be developed based on the simulation study.