Flow Characteristics in an Anatomically Realistic Compliant Carotid Artery Bifurcation Model

A numerical model for the pulsatile blood flow in an anatomically realistic compliant model of the human carotid artery bifurcation has been developed. The geometric model has been generated on the basis of an optically digitized arterial cast. The effects of the geometrically realistic flow domain and of the wall distensibility on the flow characteristics are investigated. The description of the blood flow uses the time-dependent, three-dimensional, incompressible Navier-Stokes equations for non-Newtonian inelastic fluids. The calculation of the wall displacement uses geometrically non-linear shell theory. In an iteratively coupled approach the flow equations and the shell equations are numerically solved using the finite element method. The results show strongly skewed velocity profiles with high gradients at the internal and external divider walls downstream of the bifurcation. Flow separation and recirculation occur in the regions at the outer walls of the branching during systolic flow deceleration and at the diastolic flow minimum. Further the results show complex non-symmetric secondary motion in the carotid sinus due to the slightly non-planar branching of the geometrically realistic model. At the internal divider wall high shear stress can be observed, whereas at the outer internal wall low and oscillating shear stress occurs. The comparison of the results in the realistic model with results in a geometrically idealized model primarily points out differences concerning the flow recirculation and the secondary flow pattern. Comparing the results with results of a corresponding rigid wall model demonstrates a decrease of wall shear stress magnitude and a slight reduction of flow separation and recirculation at the outer sinus wall in the distensible model. The relative decrease of the axial wall shear stress maximum is 17% at the internal divider wall. At the outer sinus wall where the shear stress is low the decrease is in the range of up to 50%.