Particle Deposition in the Lung

The deposition of aerosol in the lung is an important issue regardless of whether the aerosol results from airborne pollutants or aerosol therapy. The specific pattern of deposition of airborne pollutants is a determinant in the development of pulmonary diseases since this pattern determines the local doses in the airspaces and the subsequent redistribution and clearance of the deposited particles. Aerosol therapy allows drugs to be directly administered to injured lung tissues, where they can act more efficiently and rapidly than when administered by injection or ingestion. Deposition of inhaled aerosols can also be used as a diagnostic tool to noninvasively detect changes in the dimensions of airways and alveoli that are critically associated with the development of pulmonary pathologies such as emphysema, asthma, or bronchitis. The deposition of inhaled particles in the lung is primarily governed by the mechanisms of inertial impaction, gravitational sedimentation, Brownian diffusion, and, to a lesser extent, the mechanisms of electrostatic precipitation and interception. Deposition is minimal for particles in the size range 0.4–0.7mm that have minimal intrinsic mobility. Deposition of larger particles results from significant gravitational and inertial transport, whereas deposition of smaller particles is mainly due to diffusive transport. Apart from particle size, several factors affect particle deposition, including particle characteristics, physiological and environmental factors, and lung anatomy.