Baseline ultrasound Patients lay in bed, the back supported at approximately 45 degrees, legs lying horizontal with their knees extended. Duplex ultrasound was then performed on the superficial femoral vein (Acuson S2000, Siemens). Baseline bilateral venous assessments of peak velocity, mean velocity, volume flow and vessel diameter were taken in triplicate. All scans were performed by the same ultrasonographer for consistency. Gate size was adjusted to just within the vessel wall.