Capillary permeability of 131I-albumin in the resting human forearm

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Abstract
Study objective – The aim was to examine capillary permeability of 131I-albumin in the normal, resting human forearm. Design – A bolus injection of 131I-albumin was injected into the brachial artery, and the residue function was measured by external registration over the forearm tissues. The results were analysed by indicator kinetic "black box" theory using the single injection, residue detection method which is based on indicator diffusion principles. Subjects – Seven normal volunteers participated in the study. Measurements and main results – The mean capillary extraction fraction of 131I-albumin was 0.023 (SD 0.0056), n=7, at a mean plasma flow rate of 2.1 (0.34) ml·100 g−1·min−1. At an estimated capillary surface area of 70 cm·g−1 the permeability coefficient was 11·10−8cm·s−1. Conclusions – According to the theories of restricted diffusion and equivalent pores the results are compatible with an equivalent pore radius estimate of 113 Å using additional previously published results from experiments with 51Cr-EDTA.