Alveolar clearance: its relation to lesions of the respiratory bronchiole.

Abstract

Abstract Alveolar clearance was studied in rats following the imposition of lung dust burdens. Photomicrographs show larger concentrations of dust in the proximal portions of the racemus comprising the respiratory bronchiole and adjoining alveolar ducts, than elsewhere. Initially, this dust is largely represented as a surface coating in the proximal portion of the racemus, caused by preferential deposition at this site; but dust is also found coating the surface of peripheral alveoli. Within 3 to 4 days, most of the dust has disappeared from the surface and increased amounts of dust are now found filling the evaginating alveoli in the proximal regions of the racemus. Simultaneously, the amount of dust in the peripheral alveoli has become reduced. The respiratory bronchiole, representing the small end of a large funnel, is proposed as the critical site at which irritants tend to accumulate when the alveolar clearance mechanism is overtaxed, and this accumulation is considered to be the major reason for the tendency of lesions to begin in the proximal portion of the racemus.