title: Biomechanical properties of human ascending thoracic aortic aneurysms.
abstract: BACKGROUND
  Surgical management of ascending thoracic aortic aneurysms (aTAAs) relies on maximum diameter, growth rate, and presence of connective tissue disorders. However, dissection and rupture do occur in patients who do not meet criteria for surgical repair. This study investigated the mechanical properties of aTAAs compared with normal human ascending aortas for eventual development of biomechanical aTAA risk models.
  
  
  METHODS
  aTAA specimens (n = 18) were obtained from patients undergoing surgical aneurysm repair, and fresh, healthy ascending aortas (n = 19) as controls were obtained from the transplant donor network. Biaxial stretch testing was performed to obtain tissue mechanical properties. Patient-specific aTAA physiologic stress was calculated based on preoperative computed tomography diameter. aTAA and ascending aorta tissue stiffness at respective physiologic stress were determined.
  
  
  RESULTS
  Physiologic stress of aTAA was significantly greater (241.6 ± 59.4 kPa) than the 74 kPa for normal controls. Tissue stiffness of aTAAs was significantly greater than that of the ascending aortas at their respective physiologic stresses in the circumferential (3041.4 ± 1673.7 vs 905.1 ± 358.9 kPa, respectively; p < 0.001) and longitudinal (3498.2 ± 2456.8 vs 915.3 ± 368.9 kPa, respectively; p < 0.001) directions. Tissue stiffness of aTAAs positively correlated with aTAA diameter but did not correlate with patient age. No correlation was found between aTAA physiologic stress level and maximum aTAA diameter.
  
  
  CONCLUSIONS
  aTAAs are much stiffer than normal ascending aortas at their respective physiologic stress, which was also significantly greater in ATAAs than ascending aortas. Patient-specific physiologic stress did not correlate with maximum aTAA diameter, and patient-specific aTAA wall stress may be a useful variable to predict adverse aTAA events.
authors.affiliation: Department of Surgery, University of California at San Francisco Medical Center, San Francisco, California 94143-0118, USA.
authors.forename: Ali N
authors.initials: AN
authors.lastname: Azadani
authors.forename: Sam
authors.initials: S
authors.lastname: Chitsaz
authors.forename: Alex
authors.initials: A
authors.lastname: Mannion
authors.forename: Aart
authors.initials: A
authors.lastname: Mookhoek
authors.forename: Andrew
authors.initials: A
authors.lastname: Wisneski
authors.forename: Julius M
authors.initials: JM
authors.lastname: Guccione
authors.forename: Michael D
authors.initials: MD
authors.lastname: Hope
authors.forename: Liang
authors.initials: L
authors.lastname: Ge
authors.forename: Elaine E
authors.initials: EE
authors.lastname: Tseng
mesh_terms: D001013:Aorta, Thoracic / Q000503:physiopathology*; D017545:Aortic Aneurysm, Thoracic / Q000503:physiopathology*; D004548:Elasticity; D006801:Humans; D008875:Middle Aged; D008962:Models, Theoretical; D013314:Stress, Mechanical; D013718:Tensile Strength