title: Age-related changes in the aortic valve affect leaflet stress distributions: implications for aortic valve degeneration.
abstract: OBJECTIVE
  The degeneration of aortic valve leaflets occurs primarily due to high mechanical stresses in zones of leaflet flexion. Aging, which has been identified as a risk factor for degenerative aortic stenosis, is associated with reductions in stretch and in compliance, and an increase in tissue thickness of the leaflet and root. The study aim was to investigate the effects of age-related tissue changes on valve opening dynamics and leaflet stress patterns, and its implications for valve degeneration.
  
  
  METHODS
  A three-dimensional finite element model of the aortic valve and root was developed in Ansys. A transient, non-linear analysis was carried out of the valve opening phase. Three age groups were identified based on leaflet and root tissue properties: group I age <35 years; group II aged 33-55 years; and group III aged >55 years. The valve opening dynamics was studied and von Mises stresses in various regions of the leaflet were computed.
  
  
  RESULTS
  Maximum leaflet stresses occurred along the leaflet-root attachment, analogous to the spatial distribution of calcific deposits in the aortic valve. With increasing age, the rate of valve opening decreased, and the magnitude of leaflet tip displacement in both radial and axial directions reduced progressively. At the leaflet-root attachment, groups II and III showed 19% and 32.7% increases in average stress over group I, respectively. At the free edge, the stresses in group III increased 2.7% over group I; however, the average stress at the free edge in group II decreased 3.5% over group I. In the leaflet belly, groups II and III showed 27.6% and 60.9% increases in stresses over group I, respectively.
  
  
  CONCLUSIONS
  Changes in leaflet and root tissue properties lead to altered leaflet dynamics and increased stresses. This not only emphasizes the role of aging on the development and progression of degenerative aortic valve disease, but also has implications in the design of bioprosthetic heart valves.
authors.affiliation: Department of Chemical Engineering, University of South Florida, Tampa, Florida 33620, USA.
authors.forename: Reetu
authors.initials: R
authors.lastname: Singh
authors.forename: Joel A
authors.initials: JA
authors.lastname: Strom
authors.forename: Leo
authors.initials: L
authors.lastname: Ondrovic
authors.forename: Babu
authors.initials: B
authors.lastname: Joseph
authors.forename: Michael D
authors.initials: MD
authors.lastname: VanAuker
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology / Q000502:physiology*; D001021:Aortic Valve / Q000473:pathology / Q000503:physiopathology*; D001024:Aortic Valve Stenosis / Q000453:epidemiology* / Q000473:pathology / Q000503:physiopathology; D001696:Biomechanical Phenomena; D018450:Disease Progression; D004548:Elasticity; D020342:Finite Element Analysis; D006350:Heart Valve Prosthesis; D006801:Humans; D008875:Middle Aged; D008955:Models, Cardiovascular; D011474:Prosthesis Design; D012307:Risk Factors; D013314:Stress, Mechanical