The relative permeabilities of human conducting and terminal airways to 99mTcDTPA.

The anatomy and physiology of the pulmonary epithelial barrier are briefly described, and methods of measuring permeability of the barrier to solutes are outlined, including findings on alveolar barrier permeability to 99mTcDTPA. A method for measuring permeability to 99mTcDTPA of the conducting airways is described in which the effect of mucociliary clearance can be quantified using radio-labelled polystyrene microspheres 5 mum in diameter. When the 99mTcDTPA clearance rates from inner, intermediate and outer zones of the lungs are corrected fro the effect of mucociliary clearance, there is a significantly slower clearance from the conducting airways than from the alveoli.