Local effects of stenoses: increased flow velocity inhibits atherogenesis

Thoracic aortic coarctations were produced in cynomolgus monkeys by one of three methods: circumferential banding to produce a symmetric channel with a rigid wall, lateral plication to provide an asymmetric channel with splitting on one side, and lateral plication plus banding to provide a rigid asymmetric channel. The degree of luminal constriction was 58 +/- 12%, with no significant difference among groups. After 3-12 months on an atherogenic diet, the coarctation channels were remarkably free of lesions compared with the aorta immediately proximal to the coarctation (p less than 0.001). Banding resulted in sharp circumferential termination of the lesions just proximal to constriction. Lateral plication resulted in an oblique termination of proximal disease wtih sparing opposite the plication. Lesions distal to coarctations occurred in a pattern related to the configuration of the coarctation channel and tended to form immediately below the plication. Sparing in and immediately beyond the constriction was independent of the rigidity of the aortic wall or of previous disruptive endothelial or medial injury associated with the operative procedure. Endothelium was preserved within the coarctation channel and over all lesions and distal to the constriction. The findings suggest that flow separation and instability tend to favor atherogenesis, whereas increased flow velocity per se may exert a protective effect.