title: Differential tensile strength and collagen composition in ascending aortic aneurysms by aortic valve phenotype.
abstract: BACKGROUND
  Ascending thoracic aortic aneurysm (ATAA) predisposes patients to aortic dissection and has been associated with diminished tensile strength and disruption of collagen. Ascending thoracic aortic aneurysms arising in patients with bicuspid aortic valve (BAV) develop earlier than in those with tricuspid aortic valves (TAV) and have a different risk of dissection. The purpose of this study was to compare aortic wall tensile strength between BAV and TAV ATAAs and determine whether the collagen content of the ATAA wall is associated with tensile strength and valve phenotype.
  
  
  METHODS
  Longitudinally and circumferentially oriented strips of ATAA tissue obtained during elective surgery were stretched to failure, and collagen content was estimated by hydroxyproline assay. Experimental stress-strain data were analyzed for failure strength and elastic mechanical variables: α, β, and maximal tangential stiffness.
  
  
  RESULTS
  The circumferential and longitudinal tensile strengths were higher for BAV ATAAs when compared with TAV ATAAs. The α and β were lower for BAV ATAAs when compared with TAV ATAAs. The maximal tangential stiffness was higher for circumferential when compared with longitudinal orientation in both BAV and TAV ATAAs. The amount of hydroxyproline was equivalent in BAV and TAV ATAA specimens. Although there was a moderate correlation between the collagen content and tensile strength for TAV, this correlation is not present in BAV.
  
  
  CONCLUSIONS
  The increased tensile strength and decreased values of α and β in BAV ATAAs despite uniform collagen content between groups indicate that microstructural changes in collagen contribute to BAV-associated aortopathy.
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania; Center for Vascular Remodeling and Regeneration, University of Pittsburgh, Pittsburgh, Pennsylvania.
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Pichamuthu
authors.forename: Julie A
authors.initials: JA
authors.lastname: Phillippi
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Cleary
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Chew
authors.forename: John
authors.initials: J
authors.lastname: Hempel
authors.forename: David A
authors.initials: DA
authors.lastname: Vorp
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Gleason
mesh_terms: D000368:Aged; D001013:Aorta, Thoracic / Q000737:chemistry* / Q000503:physiopathology*; D017545:Aortic Aneurysm, Thoracic / Q000378:metabolism / Q000503:physiopathology*; D003094:Collagen / Q000378:metabolism*; D006801:Humans; D008875:Middle Aged; D010641:Phenotype; D013718:Tensile Strength / Q000502:physiology*
chemical_list: D003094:Collagen
keywords: 26; ATAA; BAV; CIRC; ECM; HYP; LONG; MTS; TAV; ascending thoracic aortic aneurysm; bicuspid aortic valve; circumferential; extracellular matrix; hydroxyproline; longitudinal; maximal tangential stiffness; tricuspid aortic valve
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