The role of elastin in aortic valve mechanics.

Recent morphologic observations of elastin structures in aortic valves suggest that elastin is mechanically coupled to collagen. Since the mechanical stiffness of elastin is considerably lower than that of collagen, and aortic valves contain relatively little elastin, the mechanical importance of elastin in heart valve function is not clear. We have hypothesized that elastin acts to return the collagen fiber structure back to a resting configuration between loading cycles. The objectives of this research were therefore to elucidate the mechanical relationship between elastin and collagen structures within the aortic valve. To isolate elastin in a morphologically intact state, whole porcine aortic valve leaflets were digested in 0.1 N sodium hydroxide solution (NaOH) at a temperature of 75 degrees C for 45 min. Elastin structures from the fibrosa and ventricularis were tested mechanically, and their loading curves compared to those of the original leaflet layers and to whole cusps. The elastin structures generated very low forces, having an elastic modulus only 0.05% that of the whole tissue. The contribution of elastin to tissue mechanics was significant at low strains and differed between the fibrosa and the ventricularis. Elastin tended to dominate the distensibility curves of the radial ventricularis, but participated very little in the fibrosa. The low but significant tensions produced by the elastin structures of the aortic valve, together with previously observed elastin morphology as well as the measurable preload of elastin, suggest that the purpose of elastin in the aortic valve leaflet is to maintain a specific collagen fiber configuration and return the fibers to this state, once external forces have been released.