This method is based on the demonstration that changes in blood volume in the calves results in changes in electrical resistance of the calves. Blood volume in the calves is altered by maximum respiratory effort or by venous occlusion by pneumatic thigh cuffs. In patients with venous obstruction, changes in electrical resistance are reduced.
This indirect method of detecting thrombosis can be inaccurate, particularly for the detection of calf vein thrombosis. It has now been largely replaced by direct duplex ultrasound scanning.
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