Background: Duplex ultrasonography has become the optimal non-invasive method of assessing the deep venous system of the leg. The stimuli used to promote reverse flow, subject positioning, and the veins scanned have varied between studies. Reverse flow of less than 0.5 s is accepted as 'normal', however, all published studies have demonstrated 'normal' subjects with deep vein reverse flow exceeding this time. The aim of this study was to establish the duration of reverse flow in all deep vein segments, and to determine the optimal method of eliciting reverse flow in individuals with proven normal deep vein function.
Methods: Duplex scanning was used to detect the presence and duration of reverse flow in the superficial femoral, popliteal and posterior tibial veins of 61 legs with normal venous function. The veins were scanned with each subject inclined at 10 degrees, 45 degrees and standing erect. The abrupt release of distal tourniquet compression and the Valsalva manoeuvre were used as stimuli for reverse flow.
Results: There was significantly less reverse flow in distal veins than in proximal veins when the subject was scanned at 10 degrees and 45 degrees. Median (range) reverse flow in the femoral vein at 10 degrees was 0.21 (0-1.18) s, posterior tibial vein 0.08 (0-0.67) s, (P < 0.0001); in the femoral vein at 45 degrees was 0.14 (0.04-2.14) s, posterior tibial vein 0.07 (0-0.56) s, (P < 0.0001). The duration of reverse flow was significantly less in the superficial femoral and popliteal veins when the subjects were erect than when inclined at 10 degrees and 45 degrees. Median (range) reverse flow in the femoral vein at 10 degrees was 0.21 (0-1.18), and when standing 0.1 (0-1.36) (P < 0.0001); below-knee popliteal vein at 10 degrees was 0.15 (0.04-1.95) s, and when standing 0.10 (0-1.03) (P = 0.0004). Reverse flow of more than 0.5 s was never elicited in the posterior tibial veins if the subject stood, nor did it occur in the popliteal vein during a Valsalva manoeuvre.
Conclusion: The optimal sites to assess deep vein reverse flow are the posterior tibial vein following removal of distal compression with the patient standing, and the popliteal vein during a Valsalva manoeuvre, as retrograde flow more than 0.5 s does not occur in subjects with normal venous function.