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Abstract
This study was designed to investigate the early stages of particle deposition on
airway and alveolar surfaces. To do this we used morphometric studies of aerosol deposition,
in situ measurements of surface tension, and in vitro assays of particle displacement
and mathematical modelling. We observed that latex particles, equal or less than 6
microns in diameter deposited in hamster lungs were submerged in the subphase of the
alveolar lining layer and became completely coated with an osmiophilic film. Similar
results were obtained for particles deposited in the conductive airways which were
also covered with a surface active film, having a surface tension of 32 +/- 2 dyn.cm-1.
In vitro experiments showed that pulmonary surfactant promotes the displacement of
particles from air to the aqueous phase and that the extent of particle immersion
depends on the surface tension of the surface active film. The lower the surface tension
the greater is the immersion of the particles into the aqueous subphase. Mathematical
analysis of the forces acting on a particle deposited on an air-fluid interface show
that for small particles (less than 100 microns) the surface tension force is several
orders of magnitude greater than forces related to gravity. Thus, even at the relatively
high surface tension obtained in the airways (32 +/- 2 dyn.cm-1) particles will still
be displaced into the aqueous subphase. Particles in peripheral airways and alveoli
likely are below the surfactant film and submerged in the subphase. This may promote
clearance by macrophages. In addition, particle displacement into the subphase is
likely to increase the contact between the epithelial cell and particle. Toxic or
allergenic particles would be available to interact with epithelial cells and this
may be important in the pathophysiology of airway disease.