Aerosol particle transport and deaggregation phenomena in the mouth and throat

The results of recent numerical simulations of aerosol particle transport and deaggregation phenomena in the mouth and throat are summarized. These results are used to comment upon the roles played by important factors influencing extrathoracic particle deposition and deaggregation phenomena. The results also provide a basis for comparing the performance of in vitro systems presently used for testing dry powder inhaler devices. Total deposition of aerosol particles in a 'physiologically faithful' three-dimensional (3D) reconstruction of the human mouth and throat closely mimics in vivo deposition data. On the other hand, aerosol particle deposition in a 3D 90 degrees -bend geometry does not accurately simulate aerosol filtration in the human mouth and throat. The numerically predicted regional deposition of aerosol particles closely matches that measured experimentally, in vitro, using the oropharyngeal cast from which the numerical reconstruction was made. A relatively weak dependence of particle deposition on flow-rate is observed with both 90 degrees -bend and 'real' oropharyngeal geometries, inconsistent with extrathoracic deposition in vivo. Two dimensional numerical simulations do not, in general, accurately simulate the conditions in the associated three-dimensional system. Quantitative differences between flow in the 90 degrees -bend and 'real' oropharyngeal geometries are especially significant in regards to the ability of the airstream to break apart particle agglomerates. For both geometries, it is observed that increasingly small particle agglomerates may be separated as the airflow rate increases from 30 to 200 lmin(-1). At flow-rates exceeding 60 lmin(-1), aggregated particles less than approximately 10-µm diameter may be separated by the airflow.