A computational model to predict aortic wall stresses in patients with systolic arterial hypertension

Computational cardiovascular mechanics has allowed scientists to create complex 3D models for the simulation of cardiovascular problems. Mechanical stress plays a crucial role in the function of the cardiovascular system; stress analysis is a useful tool for the understanding of vascular pathophysiology. By using the spiral CT imaging and computational structural analysis, we present a noninvasive method of wall stress analysis in the normal aorta. The aortic segment was extended from the origin of the inferior mesenteric artery to the aortic bifurcation. The length of this segment was 12 cm, while the maximum transverse diameter was 2.075+/-0.129 cm. A 3D aortic model was constructed based on the CT scan images. The aorta was assumed to have a uniform wall thickness of 1.5mm. The generated unstructured grid, which was used for the structural analysis, consisted of 14,440 hexahedral elements. The wall material was assumed to be hyperelastic, homogeneous, isotropic and nearly incompressible (Poisson ratio=0.45). According to experimental studies, the Young modulus of aortic wall was set equal to 4.66 MPa. The shear stress induced by the blood flow was neglected. A finite-element static structural analysis was performed. Three different cases were examined applying constant intraluminal systolic blood pressures of 120, 180 and 240 mmHg, respectively. The von Mises stress distribution and the displacements of the aortic wall were calculated. Peak wall stress for the normal load case of 120 mmHg was 22.5 N/cm2, while the max displacement was 0.44 mm. The case with the intraluminal pressure of 180 mmHg resulted into peak wall stress of 32 N/cm2 with max displacement 0.59 mm, while for 240 mmHg was 40.6N/cm2, max displacement 0.72 mm. The rise in blood pressure caused all stresses to increase. The pattern of stress distribution and the orientation of the stress were similar for all test cases. A quantitative evaluation of the aortic wall stresses under systolic hypertension is presented. The calculated values of peak wall stress are far lower to those of failure strength of healthy aortic wall specimens estimated by ex vivo mechanical testing (121.0 N/cm2). Our values are consistent with prior stress values predicted by experimental studies. The described methodology offers a significant advancement in incorporating biomechanical principles in the clinical assessment of hypertensive patients with normal or aneurysmatic aortas and can be applied in a patient-specific basis in both conditions in order to detect the vulnerable high stressed regions and the resultant risk of aortic dissection or rupture. We hypothesize that this could assist in deciding the timing of surgical intervention, especially in high-risk patients with abdominal aortic aneurysms.