COMPUTERIZED IMPEDANCE PLETHYSMOGRAPHY, A NEW PLETHYSMOGRAPHIC METHOD TO DETECT DEEP VEIN THROMBOSIS

Since the clinical diagnosis of deep vein thrombosis (DVT) is unreliable, several invasive and non-invasive methods have been developed recently. Of these, impedance plethysmography (IPG) is a widely employed technique based on measurement of changes in blood volume produced by temporary obstruction. IPG has been shovn in large prospective studies in symptomatic patients to be a safe and effective alternative to contrast venography, if used either in combination with 1251-fibrinogen legscanning or serially as a single test. Currently available impedance plethysmographs are limited by several technical and operational problems. Therefore, a new computerized impedance plethysmograph (CIP) was developed, having the following characteristics: portability, battery operated and fully automated. A prospective two-center study in 299 consecutive outpatients was done to compare the efficacy of CIP vs. venography in patients with symptomatic DVT. Using a blind design i.e. care was taken to insure that CIP and venography were performed and interpreted independently. The results in patients without venography proven thrombosis and those with proximal vein thrombosis were subjected to a discriminant analysis producing a line of best discrimination between normal and proximal vein thrombosis. In 14 patients it was not possible to obtain an adequate CIP tracing. 12 patients were not entered because of refusal to undergo venography and 15 patients were excluded from analysis because of poor opacification of the proximal veins. On the basis of discriminant analysis 138 of the CIP results were classified as normal and 120 as abnormal. 175 patients were normal on venography and 83 had proximal thrombosis. The sensitivity of CIP for proximal vein thrombosis was thus 95% while the speci-+ ficity was 77%. It is concluded that computerized impedance plethysmography is a potentially sensitive method to detect proximal vein thrombosis in patients with clinically suspected deep vein thrombosis.