A mathematic model of unilateral iliac vein obstruction was used to establish the theoretic basis for selecting saphenous vein or a larger diameter prosthetic cross-femoral venous bypass graft for relief of obstructive venous hypertension. Common femoral vein resting and postexercise peak flows, and common femoral vein and saphenous vein diameters were measured in 18 healthy individuals and used to estimate the pressure gradient (dP) across 20 cm long cross-femoral venous bypass grafts of saphenous vein or 4, 6, 8, 10, and 12 mm prosthetic conduits, in the presence of a transpelvic venous collateral network of varied cross section. The upper limits of normal for the gradients in our model (dPstd) were set at 4 mm Hg for resting flows and 6 mm Hg after exercise. Mean saphenous vein diameter was 4.3 +/- 0.22 mm, which was 36.5% +/- 1.73% of common femoral vein diameter. When the saphenous veins of two thirds of the individuals in our study were used as theoretic cross-femoral venous bypass conduits, greater than 80% of postobstruction peak cross-femoral venous bypass graft flow had to be carried by collaterals to maintain a gradient less than or equal to dPstd. We demonstrated that 4.5 to 6.0 mm diameter saphenous cross-femoral venous bypass grafts would be hemodynamically efficacious in relieving venous hypertension, but only when implanted in parallel with an existing venous collateral network that limited the preoperative dP to 4.5 to 7.5 mm Hg at resting flows and 7.0 to 11.5 mm Hg after exercise; only 44% of saphenous veins were adequate for cross-femoral venous bypass grafts by these criteria.(ABSTRACT TRUNCATED AT 250 WORDS)