Patient-Specific FSI Analysis of the Blood Flow in the Thoracic Aorta

The complexity of numerical modeling and simulation of blood flow in patient-specific thoracic aorta geometries leads to a number of major computational challenging issues. For instance, for an adequate simulation of the flow and pressure field, the incompressible Navier-Stokes equations have to be solved with the assumption that the relatively thin blood vessels suffer large displacements and undergo large elastic or visco-elastic deformations caused by the pulsatile blood flow. Subsequently, inaccurate predictions would be obtained for the hemodynamic quantities with the very simplifying rigid-wall assumption (CFD modeling). Moreover, when applying only the CFD modeling approach the essential phenomena of pressure wave propagation in cardiovascular systems are disregarded, however these phenomena are of major relevance for clinical practice. Accordingly, strongly coupled FSI schemes are inevitable for comprehensive blood flow simulations in arterial systems, and as blood and vascular walls have comparable densities, monolithic or at least partitioned strongly coupled FSI schemes are required for solving the multi-physics problem with its inherent significant added-mass effects.

Furthermore, the quality of a patient-specific simulation is also affected by other factors, including both by the accuracy of the model generated from the medical imaging data and by the outlet boundary condition settings. For the former, the key challenges, among others, are to incorporate the varying vessel wall thicknesses and material properties into the solid model and to consider the varying influence of surrounding tissues and organs on the vessel wall deformations (external tissue support). Moreover, of particular importance are the outflow boundary conditions at the thoracic aorta branch outlets, because these boundary conditions have a fundamental impact both on the development of the blood flow and on the pressure field distribution. For the simulation of the hemodynamics in large vessels, standard outlet boundary conditions are inappropriate for reproducing realistic flow results, while enforcing, at the same time, patient-specific outlet volume flow rates at the branch exits of the model. In this context, a well-established approach for imposing boundary conditions is to employ the three-element windkessel model on each outlet, where a model mimics the resistance and capacitance of the downstream arterial network of the respective outlet based on patient-specific calibrated parameters.

Poster Downloads

FSI Aorta Poster: Part 1

FSI Aorta Poster: Part 2