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SUMMARY Autologous femoral veins grafted between the external iliac arteries in 18 dogs provided a model for studying the hemodynamics and histopathology of vein graft bypasses. The angle of proximal anastomosis was varied by groups (<90°, 90°, >90°) to produce a wide range of flow conditions within the grafts. Four months after implantation, point velocity measurements of blood flow and histological examination of the superior and inferior walls were made at proximal, middle, and distal locations in each graft. Hot-film velocity measurements revealed outwardly skewed velocity profiles in the proximal locations in all grafts, and flow visualization models showed secondary fluid motions and separation zones at those regions. Velocity profiles in the middle and distal regions of the grafts were more symmetrical and showed no flow separation. Histological examination of wall sections along the graft length showed that intimal proliferation occurred focally and ranged from 1 to 100 fita in thickness. No signficant correlation between graft angle and degree of intimal proliferation was found. However, there was a weak inverse correlation between the apparent fluid shear rate and the corresponding degree of intimal proliferation, with the greatest proliferation occurring in the regions experiencing the lowest shearing forces. Regions of low shear rate should be avoided by maintaining adequate flow rates through the grafts and thus minimising losses of patency due to both thrombus formation and intimal proliferation.

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The effects of the number of stenoses and the distance between consecutive stenoses on the total pressure drop across a series of noncritical stenoses with 50 percent area reduction were determined experimentally. The mean flow rate was varied to correspond to a Reynolds number range of 30–280 and both in vitro and in vivo measurements of the pressure drop were carried out. Flow visualization studies also were performed. The pressure drop across a series of stenoses was found to increase linearly with the number of stenoses. Comparable results were obtained from the steady and pulsatile flow in vitro experiments as well as from the in vivo experiments. The results indicate that the total effect of a series of noncritical stenoses is approximately equal to the sum of their individual effects and that the combined effect of a series of noncritical stenoses thus can be critical.

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