Dynamics of oropharyngeal aerosol transport and deposition with the realistic flow pattern

Aerosol flow and deposition in the model of human oropharynx was studied theoretically and experimentally for two realistic inspiratory patterns. The three-dimensional (3D) airflow structure in the sample geometry was solved with the computational fluid dynamics (CFD) code (Fluent), used to calculate dynamic distribution of particle deposition (0.3-10 mum). Experiments were done for the same flow conditions using the silicone-rubber cast with the matching geometry. Nonsteady breathing flows were reproduced with the computer-controlled artificial lung apparatus. Results of computations show that particles smaller than 3 mum easily pass the oropharynx during inspiration, while particles with a size close to 10 mum are substantially deposited, preferentially in the region of the naso-pharyngeal bend. For particles in the submicrometer size range, the spatial and temporal deposition pattern is more complicated, and strongly depends on breathing dynamics. The experiments confirmed that the mass median diameter (MMD) of the aerosol that penetrates the oropharynx and flows to the tracheobronchial tree is reduced. Measured total mass efficiency of deposition of the tested aerosol was in the range of 35-60%, depending on the breathing pattern. These findings are consistent with the CFD results. The methods and the preliminary results enable a more realistic analysis of dynamic effects during the flow of inhaled particles through the complex geometry of the oropharynx. Such analysis is needed for estimation of toxic potential of aerosols, related to their local deposition in different parts of the respiratory tract.