A model approach for calculating the net capillary filtration rate during venous occlusion

The venous occlusion method is commonly used to measure the net capillary filtration rate, calculated from the slope of the increasing volume curve of the limb at a given time. However, this technique does not take variation in the rate of venous filling into account. In the present study, a model of sum of two cumulative exponential functions was developed to describe the venous filling phase and the increase in interstitial fluid volume due to the net capillary filtration rate. The model was tested on 15 normal subjects and eight patients with post-thrombotic venous insufficiency. The cumulative exponential model gave a good description of the changes in volume that occur during venous occlusion. The model also enabled determination of the net CFR at the same phase of the maximal venous capacity.