Patient-specific local and systemic haemodynamics in the presence of a left ventricular assist device

Abstract

The ability to accurately and efficiently simulate cardiovascular dynamics has the opportunity to improve the diagnosis and intervention of vascular disease. Due to a reducing number of donor hearts, left ventricular assist devices (LVAD - mechanical blood pumps) are gaining prevalence in the treatment of severe left ventricular dysfunction. The interaction of the LVAD and native cardiovascular system is the main focus of this thesis. Computational fluid dynamic (CFD) models, of varying complexity and structure, are applied to a patient-specific aorta in the presence of a left ventricular assist device. The downstream boundary conditions of the CFD model are described initially as a simple Windkessel model before embedding the 3D domain in a closed loop 0D description of the entire cardiovascular system, incorporating models of the heart valves, chambers and the blood pump. It is shown that a turbulence model is required to simulate the haemodynamics of the assisted aorta and a compressible fluid, tuned to produce a desired wave speed, gives an accurate and efficient approximation of the wave propagation effects induced by the interaction between the blood and the elastic vessel wall. A series of CFD simulations, employing the complex 0D description of the assisted cardiovascular system, investigated the conditions under which the aortic valve opens during left ventricular support. It is found that, for a patient with moderate heart failure, the aortic valve will open when the Berlin Heart INCOR LVAD is operating at speeds of less than or equal to 5000 rpm.