Blunt trauma and acute aortic syndrome: a three-layer finite-element model of the aortic wall.

OBJECTIVE The exact process by which blunt trauma to the aorta produces a typical characteristic lesion set of primary, transverse, intimal injury remains unknown. The likely cause is a combination of intraluminal hypertension and mechanical deformation. We set about creating a three-layer finite-element model of the aorta. We hypothesised that deformation of the aorta through tension, torsion and bending would have differential effects on the constitutive layers of the aorta and this differential stress strain pattern would help to explain the mechanism of this injury. METHODS A finite-element model of the aorta was created with three distinct layers representing tunica intima, media and adventitia. A rubble-like material model in the commercial dynamic finite-element package LS-DYNA was adopted. Numerical methods for considering the interaction between aortic tissue (solid) and blood (fluid) were defined using arbitrary Lagrangian Eulerian methods. Simulations of mechanical deformation including tension, torsion and bending were applied with loading set at 1m/s and intraluminal blood pressure rising from 86.6mmHg to 146mmHg. The simulations were run until material failure. The role of blood within these simulations was explored. RESULT Our initial simulations confirmed the functionality of the three-layer finite-element model of the aorta with behaviour as expected from previously published experimentation. The addition of mechanical loading through torsion, tension and bending resulted in failure of the aorta at significantly lower mean blood pressures than without. Temporal and spatial aspects of failure were distinct for each method of loading. Bending resulted in rapid primary adventitial failure while tension and torsion resulted in a relatively delayed primary intimal failure. Blood flow altered the stress strain characteristics within the model. CONCLUSIONS This work confirms the feasibility of using a three-layer FE model of the aorta. Our data suggest that the relative contribution of intraluminal hypertension to BTAR is lower in the presence of complex loading by tension, torsion and bending. In addition, failure of the aorta is load dependent with bending causing a relatively early primary adventitial failure, while tension and torsion result in a relatively delayed primary intimal failure.