Aortic valve cusp vessel density: relationship with tissue thickness.
OBJECTIVE
The presence of a microvasculature within aortic cusps implies that tissue oxygen requirements exceed the amount deliverable by diffusion from the tissue surfaces alone. For the design of a successful tissue-engineered valve replacement, the effect of diffusion distance (tissue thickness) on oxygen delivery must be considered. We therefore examined in normal aortic valve cusps the relationship between the presence of microvessels and the tissue thickness.


METHODS
Thirty porcine aortic valve cusps were excised and examined after cusp microvessels were pressure filled with a carbon particle solution. Cusp images were captured for stereographic vessel density analysis, and cusp thickness was determined with a radiographic technique. Histologic cross-sections were evaluated to determine vessel depth from the cusp surface.


RESULTS
Cusp basal regions measured 0.69 to 0.86 mm in thickness, significantly thicker (P =.001) than the rest of the cusp, which measured 0.36 to 0.48 mm. In general a vascular bed was present when cusp thickness exceeded 0.5 mm, with a median value of 5.16 vessels/mm(3).


CONCLUSIONS
From published values of arterial wall oxygen consumption and diffusivity, we predicted that the probable maximum oxygen diffusion distance for valve tissue would be about 0.2 mm. This was consistent with our physical findings, which implies that central tissue anoxia is avoided by the capillary bed. An avascular tissue-engineered valve metabolically similar to an aortic valve should therefore not exceed a thickness of approximately 0.40 mm.
Weind
K L
KL
Heart Valve Laboratory, The John P. Robarts Research Institute, University of Western Ontario, London, Ontario, Canada.
Ellis
C G
CG
Boughner
D R
DR
D000818:Animals; D001021:Aortic Valve / Q000033:anatomy & histology / Q000378:metabolism; D001705:Bioprosthesis; D006350:Heart Valve Prosthesis; D008833:Microcirculation; D010101:Oxygen Consumption; D011474:Prosthesis Design; D013552:Swine