The influence of limb elevation, examination technique, and outflow system design on venous plethysmography.

The effect of limb elevation and the design of the thigh cuff outflow system on venous capacitance and venous outflow, as determined by strain gauge plethysmography, was reviewed in a group of normal limbs without evidence of deep venous thrombosis. We improved the reliability of plethysmography in evaluating venous outflow, particularly in the early period after cuff deflation, by using uniform leg elevation, large diameter outflow tubing, and single rather than simultaneous limb examinations. Based on this experience, an optimum technique of examination emphasizing precise limb elevation, sequential limb examination and proper design of the cuff outflow system was used to evaluate 21 patients with acute venous thrombosis. The results obtained were compared with previously reported results of strain gauge plethysmography in patients with acute venous thrombosis. This technique significantly reduced the incidence of false-positive results.