Bilateral impedance rheography with a respiratory maneuver has proven useful in the diagnosis of limb deep venous thrombosis. However, both false positive and false negative results have occurred with this method.
Using an inspiratory maneuver, 22 of 50 "normal" volunteer limbs had false positive results. When the Valsalva maneuver was used, all limb impedance responses reverted to normal. In 64 patients 23 had false positive tests with the inspiratory maneuver but were normal when the Valsalva maneuver was used. Eight patients with phlebographic proof of deep venous thrombosis had positive results with either respiratory maneuver. False negative results in five patients were reverted by placing tourniquets snugly around the thigh. Impedance rheography remains a useful screening procedure for the detection of limb deep venous thrombosis.