title: Aneurysm wall stress and tendency to rupture are features of physical wall properties: an experimental study.
abstract: OBJECTIVE
  To use bench top techniques to examine the biophysical phenomena affecting the risk of abdominal aortic aneurysm (AAA) rupture relative to the physical properties of the aneurysm sac.
  
  
  METHODS
  Three latex AAAs with different wall elasticities were tested in a validated pulsatile flow model (PFM). Strain gauges were wired to each AAA model at the neck, inflection point, and at the maximum diameter. In initial studies, the influence of pressurization and the mechanical properties of AAA wall stress were evaluated. In subsequent studies, the latex AAAs were excluded with a tube graft and retested in the PFM. After creation of either a type I or II endoleak of known size and pressure, the systemic/intrasac pressure and the AAA wall stress were measured.
  
  
  RESULTS
  Each model had a complex wall-stress pattern comprising radial, longitudinal, and shear components. The peak wall stress at any point, in the presence of systemic pressurization or endoleak pressure, only reached 1% of the failure strength. In an AAA with a reinforced wall, the peak stress was significantly greater. Statistical analysis showed that wall strength contributed more significantly to wall stress than increasing pressurization within the AAA sac.
  
  
  CONCLUSIONS
  AAA wall mechanics contribute more significantly to peak wall stress than pressure variations within the system. In particular, increased stiffness (analogous to collagen deposition) significantly increased peak wall stress, which was located at the inflection point rather than at the maximum diameter. Techniques to measure the AAA wall mechanics and the rate of deterioration may predict AAA rupture in the untreated state or in the presence of an endoleak following endovascular repair.
authors.affiliation: Vascular/Endovascular Unit, University College, London Hospitals NHS Trust, London, England, UK.
authors.forename: Harpaul S
authors.initials: HS
authors.lastname: Flora
authors.forename: Bijan
authors.initials: B
authors.lastname: Talei-Faz
authors.forename: Leslie
authors.initials: L
authors.lastname: Ansdell
authors.forename: Edmund J
authors.initials: EJ
authors.lastname: Chaloner
authors.forename: Aaron
authors.initials: A
authors.lastname: Sweeny
authors.forename: Anthony
authors.initials: A
authors.lastname: Grass
authors.forename: Mohan
authors.initials: M
authors.lastname: Adiseshiah
mesh_terms: D017544:Aortic Aneurysm, Abdominal / Q000150:complications* / Q000503:physiopathology*; D001019:Aortic Rupture / Q000209:etiology* / Q000503:physiopathology*; D004548:Elasticity; D006801:Humans; D066298:In Vitro Techniques; D008955:Models, Cardiovascular; D011312:Pressure; D011673:Pulsatile Flow / Q000502:physiology; D012307:Risk Factors; D013314:Stress, Mechanical