Deposition of Particles in Human Mouth-Throat Replicas and a USP Induction Port

Oral inhalation is the common route of drug delivery to pulmonary airways. In general, deposition in the oropharyngeal airways from a drug-delivery device makes up a substantial portion of the emitted dose, which affects the dose delivered to the lung. Studies with airway replicas made from cadaver or magnetic resonance imaging scans show that for micrometer-sized particles, impaction is the dominant deposition mechanism. Several deposition studies in oropharyngeal replicas found that the deposition efficiency can be correlated with the mouth inlet velocity and inlet mouthpiece diameter. Other studies show that the deposition efficiency is best correlated with the mean diameter of internal geometry and the mean velocity based on the mean diameter.

We investigated the mouth inlet diameter, as well as internal airway dimensions and their influence on oropharyngeal deposition based on experimental data from this study. Several human oropharyngeal replicas with different mouth inlet diameters and the USP induction port were used.

We found that the aerosol deposition increased with decreasing mouth inlet diameter. Several mathematical expressions were tried to correlate the deposition efficiency with the Stokes number calculated based on (1) mouth inlet diameter and inlet velocity, (2) mean diameter of internal geometry and mean velocity, (3) mouth inlet velocity and mean diameter, and (4) mouth inlet velocity and minimum diameter in the oropharyngeal replica. The best correlation was obtained in case 4.

This correlation could explain the intra-subject variation when deposition was found to vary with mouth inlet diameter, such as in some aerosol drug-delivery devices. It could also explain the intersubject variability in oropharyngeal deposition when human volunteers with different airway geometries and mouth openings were studied.