AIM: The aim of this pilot study was to assess the venous hemodynamic changes after deep venous thrombosis (DVT) using air-plethysmography (APG) and to study the rate and magnitude of these changes in relation to those associated with the post-trombotic syndrome.METHODS: Twenty limbs of 19 patients with acute iliofemoral thrombosis have been followed up with APG and Duplex scanning for 24 months. Patients were treated with anticoagulation and elastic stockings. The air-plethysmographic measurements of venous outflow and functional venous volume were measured on admission. These measurements, as well as venous reflux and calf muscle pump ejecting capacity, have been performer after one week, one month and 3, 6, 12, 18 and 24 months. The results were compared with similar measurements of 10 normal limbs and 10 post-thrombotic limbs with chronic venous ulcers. Duplex scanning was performed on admission, in six and 24 months.RESULTS: Plethysmographic parameters showed a dramatic improvement in the first month, fast improvement after three months and slower improvement thereafter, with the exception of the development of marked venous reflux in five of the 20 limbs studied, in the first three months. Popliteal reflux was diagnosed in these limbs. Elastic compression protected the patent veins from overdistention and incompetence and contributed to the relatively good calf muscle pump function during the first year after DVT. By the end of the study no patient had post-thrombotic changes, but four patients needed elastic stockings in order to avoid edema.CONCLUSIONS: The most important hemodynamic alterations occurred during the first three months after DVT. This is the crucial period during which conservative treatment needs to be improved. Further work is required in this field to study the effect of various newly emerging methods. The air-plethysmographic measurements described may become surrogate endpoints for testing different therapies.