The Effect of Particle Size on the Regional Deposition of Inhaled Aerosols in the Human Respiratory Tract

Abstract The effect of particle size on the regional deposition of aerosols inhaled through the mouth was determined in 93 studies on 34 subjects. The test aerosols were spherical monodisperse insoluble iron oxide particles (specific gravity 2.5) containing radioactive tags, ranging in median unit density diameter from 2.1 to 12.5-microns (σ ≅ 1.08). Particles deposited on the bronchial tree were translocated to the stomach by mucociliary clearance which was essentially complete within the first day. The proportion of the initial lung burden of radioactive particles removed during the first 24 hours provided a functional measure of tracheo-bronchial deposition. A portion of the inhaled aerosol was deposited in the head by impaction. As an impactor, the tracheobronchial tree is more efficient. For each individual subject, head and tracheobronchial deposition increased with increasing particle size. Alveolar depositions decreased with size for particles larger than 4-microns.