The development of a numerical tool for estimating stenosis functional significance in human diseased coronary arteries -

Abstract

This thesis reports on a new boundary condition formulation to model the total coronary myocardial flow and resistance characteristics of the myocardial vascular bed for any specific patient when considered for noninvasive diagnosis of ischemia. The developed boundary condition model gives an implicit representation of the downstream truncated coronary bed. Further, it is based on incorporating patient-specific physiological parameters that can be noninvasively extracted to account for blood flow demand to the myocardium at rest and hyperemic conditions. Prior to the formulation of the outflow boundary condition model, a coupled 3D arterial-coronary bed impedance model was considered. Unlike other blood flow waveforms in the systemic circulation, coronary flow has a complex morphology and is affected by the contraction and relaxation forces of the heart. To realistically simulate the transient behavior of the coronary flow following the cardiac cycle phases, the heart effects on the coronary arteries have to be included. For that purpose, an electric circuit representation is integrated to model the truncated downstream coronary bed based on the analogy between electric and hydrodynamic methods. Such representation reflects the impedance of the downstream coronary bed and can be viewed as a proximal 3-element Windkessel part combined to a distal part which is dependent on the cardiac contraction phase. The lumped coronary impedance model (representing the truncated downstream coronary arterial network) which is used as an outlet boundary condition to the 3D domain (coronary artery to be diagnosed), allows to simulate normal and pathological conditions such as disease in the microcirculation. Theoretical and computational analysis was performed on the downstream coronary bed model, and results indicated the important role of the resistive elements of the coronary bed in determining FFR. Other terms (including the compliant elements and intramyocardial pressure) were shown to have no impact. Furthermore, a computa