Fluid–structure interaction study for biomechanics and risk factors in Stanford type A aortic dissection

Abstract

Aortic dissection is a life-threatening condition with a rising prevalence in the elderly population, possibly as a consequence of the increasing population life expectancy. Untreated aortic dissection can lead to myocardial infarction, aortic branch malperfusion or occlusion, rupture, aneurysm formation and death. This study aims to assess the potential of a biomechanical model in predicting the risks of a non-dilated thoracic aorta with Stanford type A dissection. To achieve this, a fully coupled fluid-structure interaction model was developed under realistic blood flow conditions. This model of the aorta was developed by considering threedimensional artery geometry, multiple artery layers, hyperelastic artery wall, in vivo-based physiological time-varying blood velocity profiles, and non-Newtonian blood behaviours. The results demonstrate that in a thoracic aorta with Stanford type A dissection, the wall shear stress (WSS) is significantly low in the ascending aorta and false lumen, leading to potential aortic dilation and thrombus formation.The results also reveal that the WSS is highly related to blood flow patterns. The aortic arch region near the brachiocephalic and left common carotid artery is prone to rupture, showing a good agreement with the clinical reports. The results have been translated into their potential clinical relevance by revealing the role of the stress state, WSS and flow characteristics as the main parameters affecting lesion progression, including rupture and aneurysm. The developed model can be tailored for patient-specific studies and utilised as a predictive tool to estimate aneurysm growth and initiation of wall rupture inside the human thoracic aorta.

On the role of tissue mechanics in fluid–structure interaction simulations of patient‐specific aortic dissection

“…To fully exploit the model complexity when postprocessing the stresses, the anisotropic material properties were taken into account in tissue stress measures. Related works are based on the von Mises stress 20,21 or the maximum principal stress, 34,80 but none of these works relate the Cauchy stress directly to the microstructure orientation of the vessel. In this work, we investigated the spatio‐temporal distribution of the latter stress measure, but also included the normal and tangential traction components of the tissue.…”

“…The generalized Newtonian fluid models employed in this work are characterized by a variable viscosity $$$ {\mu}_f={\mu}_f\left(\dot{\gamma}\right) $$$, which is a function of the shear rate $$$ \dot{\gamma} $$$, that is, $$$$ \dot{\gamma}:= 1/2\sqrt{\nabla^s\boldsymbol{u}:{\nabla}^s\boldsymbol{u}},\kern2em \mathrm{with}\kern2em {\nabla}^s\boldsymbol{u}:= 1/2\left(\nabla \boldsymbol{u}+\nabla {\boldsymbol{u}}^{\mathrm{T}}\right), $$$$ such that the Cauchy stress tensor can be expressed as $$$$ {\boldsymbol{\sigma}}_f:= -p\boldsymbol{I}+2{\mu}_f{\nabla}^s\boldsymbol{u}. $$$$ In the context of vascular flow, prominent choices are the Quemada, 21 Carreau‐Yasuda, 13,16,18,42 or the Carreau 31 model, capturing the shear‐thinning behavior of blood. The latter rheological law can be expressed as …”

“…Continuum mechanics approaches can be fruitfully used to study stresses and strains in tissue, as demonstrated by Wang et al 21 Based on a case with a nondilated thoracic aorta with type A dissection, a two‐layered (intima and adventitia) patient‐specific model was constructed that coupled the Holzapfel–Gasser–Ogden model for the tissue and a non‐Newtonian fluid including a turbulence model. WSSs in the false lumen were found low in the false lumen and promoted thrombus growth and aortic dilatation, while the maximum von Mises stress in the tissue was found near the bracchiocephalic artery and the stresses in the intima were, on average, higher than those in the adventitia.…”

Modeling Dynamics of the Cardiovascular System Using Fluid-Structure Interaction Methods

“…The predictive capabilities of a biomechanical model in evaluating the risks associated with a non-dilated thoracic aorta affected by Stanford type A dissection, a life-threatening condition, are assessed in [52]. A comprehensive FSI model was developed, considering realistic blood flow conditions, three-dimensional artery geometry, multiple artery layers, and in vivo-based physiological factors.…”