The effect of rigid external support on vein graft adaptation to the arterial circulation.

In previous experiments vein graft wall thickening stopped when the ratio of lumen radius to wall thickness equaled that of a normal artery. This led us to postulate that wall stress, which this ratio determines, regulates wall structure. To test this hypothesis we studied the effect of decreasing lumen radius and acutely diminishing wall stress with a rigid, external support. Jugular vein grafts were interposed into the carotid artery of rabbits. The proximal half of the grafts was wrapped with a polytetrafluoroethylene graft. Twelve veins received a tight wrap (2.5 or 3 mm diameter) that decreased the graft diameter, and four received a loose wrap (5 mm diameter) that did not. These grafts were fixed by perfusion after 1 day, 11 days, or 12 weeks. Wall thickness was slightly less in all tight-wrap segments. Total cross-sectional wall area, smooth muscle cell volume, and matrix deposition were significantly reduced in tight-wrap segments. These differences were greatest at 11 days. The observation that narrowing and external support of these vein grafts causes reduction of wall area supports the hypothesis that increased wall stress might be an important stimulus for wall thickening.