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An estimate of changes in body or limb volume may be made using a strain gauge around the chest or limb. The usual transducer for this is a silicon-rubber tube containing a thin thread of mercury. As volume changes occur the strain gauge will exhibit changes in resistance which can be detected in a suitable bridge circuit. The best known application of this device is the venous occlusion plethysmograph in which pulsation in the limb may be detected, or more commonly the blood perfusion rate may be estimated by restricting the venous return from the limb for a short period (by a pressure cuff at say 50 mmHg) and recording the rate of rise of volume of the limb or limb segment. Similar information may be gained using inflated cuffs around the limb coupled to air flow or pressure transducers.
Such devices might be used by vascular or orthopaedic surgeons to assess the quality of blood perfusion in diseased limbs.
Content and Design Copyright 2000 Dr. Malcolm C Brown. See Title Page for more details