Age-dependent changes in the radial stretch of human aortic valve leaflets determined by biaxial testing.

The maximum radial elastic extensibility (stretch) of human aortic valve leaflets was measured as a function of the donor age using biaxial testing techniques. The 36 leaflets tested were removed from 18 unimplanted cryopreserved aortic allograft valves retrieved from donors aged 15 to 58 years. The stretch was measured at a traction of 60 Nm-1 and analyzed as a function of the age of the donor. It was found that at 15 years, the radial stretch is about 80% but declines rapidly (linearized rate of 4% per year) to be 40% by the age of 25 years. The stretch stays approximately constant until the age of 40 years and then undergoes a steady decline at the rate of about 1% per year at least until the age of 58 years. These results demonstrate that stretch, which is important for the maintenance of adequate coaptation area, is not permanent but may be lost at a relatively rapid rate for reasons that are not yet understood. Stretch loss in the leaflets also must be a contributing factor to the development of aortic incompetence. The probability of postoperative stretch loss needs to be allowed for in sizing protocols for aortic allografts.