Deposition pattern of inorganic particles at the alveolar level in the lungs of rats and mice.

The early pathogenesis of particle-induced lung disease is likely to be determined in large part by the initial pattern of dust deposition at the alveolar level. We have studied the deposition pattern of 5 aerosolized dusts (chrysotile and crocidolite asbestos, fiber glass, alpha-quartz, and ash from Mt. St. Helens) in the lungs of rats. Mice were exposed to chrysotile asbestos. Quantitative electron microscopy was carried out on tissues fixed by vascular perfusion. Immediately after a brief exposure, significantly (p less than or equal to 0.01) greater numbers of particulates had deposited on alveolar duct bifurcations when compared with the number of particles on duct surfaces adjacent to the bifurcations. Few particles were counted at midpoints between bifurcations, and particles rarely were observed within alveoli. Our data show that regardless of mineral nature, shape, or concentration, inhaled particulates small enough to pass through the conducting airways are deposited primarily at alveolar duct bifurcations. We proposed that the alveolar deposition patterns observed are the result of air-flow characteristics that cause enhanced deposition of particles at alveolar duct bifurcations intersecting the flow. This is similar to deposition patterns that occur at bifurcations of conducting airways.