Deposition Patterns of Polydisperse Aerosols Within Human Lungs

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Abstract
The efficacy of airborne pharmaceuticals in the treatment of lung diseases can may be improved with the selective deposition of inhaled drugs. Herein, a validated mathematical model is used to examine the effects of aerosol polydispersity upon deposition in the human lung. Localized deposition patterns are calculated on an airway generation-by-generation basis. For log-normal particle size distributions, as produced by metered-dose inhalers (MDIs) and nebulizers, deposition efficiencies are shown to be sensitive functions of the mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD). The relevance of the count median diameter (CMD) of a log-normal distribution is also examined. To explain the deposition patterns of inhaled aerosols, the efficiencies of the separate mechanisms of inertial impaction, sedimentation, and diffusion are examined as functions of flow rates and particle sizes. To demonstrate applicability, the model is used to simulate the clinical inhalation exposure tests of Newman et al. [1989, 1991a] using dry powder inhalers (DPIs) and MDIs. The agreement between between theory and experiment indicates that the behavior of inhaled particles is accurately modeled. The model provides a heretofore unavailable basis for interpreting the information obtained from gamma camera lung scans. Therefore, it may aid in the design of future drug delivery tests.