EFFECT OF MUCUS HYPERSECRETION ON INITIAL TIME COURSE OF INERT PARTICLE CLEARANCE FROM THE LUNG

For radiation hazard estimation it is convenient to characterise retention of inhaled particles in the lung as a sum of exponentials representing clearance from different regions of the normal lung. When mucociliary transport is impaired, this characterisation may work less well. Subjects with impaired mucociliary clearance and mucus hypersecretion clear particles partly by the back-up lung defence mechanism of cough. This study aims to describe and model clearance by cough and also the underlying time-course of "non-cough" clearance of insoluble radiolabelled polystyrene particles over the first 24 h after inhalation. The model chosen was a simplified version of that proposed by the International Commission on Radiological Protection, (ICRP, 1994), with only three exponentially clearing compartments analogous to the bronchial, bronchiolar and alveolar-interstitial compartments of that model. The "alveolar interstitial" compartment was used to accommodate all the slow clearing compartments of the lung since the differences between them are negligible for this study. Most of these are effectively constant over the first 24 h. In addition we considered that a fraction of the other two compartments would be cleared exclusively by cough and could therefore be treated as a separate "cough compartment".