Local mechanical and structural properties of healthy and diseased human ascending aorta tissue

Objective: This study investigates the mechanics and histology of healthy and dilated human ascending aortas (AA). The regional variation in mechanical response and tissue structure were compared. Methods: Rings of human AA From healthy (n=5), dilated tricuspid aortic valve (TAV, n=5), and dilated bicuspid aortic valve (BAV, n=6) patients were mechanically tested. Each aortic ring was sectioned into quadrants-anterior, posterior, medial (inner Curvature) and lateral (Outer curvature). Low- and high-stress elastic moduli Were calculated from the equibiaxial stress strain curve to determine the local mechanical properties. Histological analysis was used to quantify the percent composition of elastin. collagen, and smooth muscle cells. Results: BAV tissue was thinnest and contained the far est percent composition of collagen. Both TAV and BAV tissue had significantly less elastin than healthy tissue. At low strain in the circumferential direction, TAV tissue was oil average the least stiff. The elastic modulus was dependent oil quadrant and tissue type but not direction (isotropic). Generally the lateral quadrant tissue was the stiffest and the medial quadrant the least stiff. There were no apparent local variations in the tissue histology. Conclusions: Local variations in tissue thickness and mechanical properties were evident in all samples analyzed and may be linked to the type of aortic valve present. (C) 2009 Elsevier Inc. All rights reserved.