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Purpose. It has been reported clinically that rupture or dissections inthoracic aortic aneurysms (TAA) often occur due to hypertension which may bemodelled with sudden increase of peripheral resistance, inducing acute changesof blood volumes in the aorta. There is clinical evidence that more compliantaneurysms are less prone to rupture as they can sustain such changes of volume.The aim of the current paper is to verify this paradigm by evaluatingcomputationally the role played by the variation of peripheral resistance andthe impact of aortic stiffness onto peak wall stress in ascending TAA. Methods.Fluid-Structure Interaction (FSI) analyses were performed usingpatient-specific geometries and boundary conditions derived from 4D MRIdatasets acquired on a patient. Blood was assumed incompressible and wastreated as a non-Newtonian fluid using the Carreau model while the wallmechanical properties were obtained from the bulge inflation tests carried outin vitro after surgical repair. The Navier Stokes equations were solved inANSYS Fluent. The Arbitrary Lagrangian Eulerian formulation was used to accountfor the wall deformations. At the interface between the solid domain and thefluid domain, the fluid pressure was transferred to the wall and thedisplacement of the wall was transferred to the fluid. The two systems wereconnected by the System Coupling component which controls the solver executionof fluid and solid simulations in ANSYS. Fluid and solid domains were solvedsequentially starting from the fluid simulations. Results. Distributions ofblood flow, wall shear stress and wall stress were evaluated in the ascendingthoracic aorta using the FSI analyses. We always observed a significant floweccentricity in the simulations, in very good agreement with velocity profilesmeasured using 4D MRI. The results also showed significant increase of peakwall stress due to the increase of peripheral resistance and aortic stiffness.In the worst case scenario, the largest peripheral resistance (10 10 kg.s.m-4)and stiffness (10 MPa) resulted in a maximal principal stress equal to 702 kPa,whereas it was only 77 kPa in normal conditions. Conclusions. This is the firsttime that the risk of rupture of an aTAA is quantified in case of the combinedeffects of hypertension and aortic stiffness increase. Our findings suggestthat a stiffer TAA may have the most altered distribution of wall stress and anacute change of peripheral vascular resistance could significantly increase therisk of rupture for a stiffer aneurysm.

Evaluation of Peak Wall Stress in an Ascending Thoracic Aortic Aneurysm Using FSI Simulations: Effects of Aortic Stiffness and Peripheral Resistance