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The Journal of Thoracic and Cardiovascular Surgery, Vol 92, 29-36, Copyright © 1986 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association

ARTICLES

Comparison of the in vivo and in vitro mechanical properties of aortic valve leaflets

MJ Thubrikar, J Aouad and SP Nolan

The mechanical properties of aortic valve leaflets are responsible for the efficiency and longevity of the valve. These properties in the radial direction were investigated in vivo in dogs. During cardiopulmonary bypass, radiopaque markers were placed on the leaflets. Later, from a normally functioning valve, the marker positions were recorded on videotape during fluoroscopy, and the leaflet length was determined. Leaflet length in the radial direction increased 31% from systole to diastole. During diastole, leaflet length increased by 3.9% as the pressure gradient increased from 60 to 200 mm Hg. During systole, the leaflet had a low elastic modulus. In vitro, the stress- strain properties of the leaflets were studied. For an increase in stress in vitro that corresponded to an increase in pressure gradient from 60 to 200 mm Hg, the leaflet length increased 8.7%. This increase was more than twice that measured in vivo, which indicates that during diastole the leaflet is much stiffer in vivo than in vitro. This stiffening appears to be due to stress in the circumferentially oriented collagen fibers of the leaflet, which prevents stretching in the radial direction. In systole, the lower elastic modulus reduces the flexion stresses, and in diastole, stiffening prevents the leaflet from prolapsing under pressure.

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