Parametric study on mouth–throat geometrical factors on deposition of orally inhaled aerosols

There is a growing need to select a realistic mouth–throat (MT) model to replace the USP induction port (IP) which underestimates MT deposition of inhaled particles. Even though there are many image-based MT models in literature, substantial inconsistencies exist regarding the critical geometrical factors that affect the MT deposition. The objective of this study was to systematically evaluate the relative importance of MT geometrical factors that affect the deposition of orally inhaled aerosols, which include the oral cavity volume, glottis area, airway curvature, and MT airway volume. Four existing MT models with different level of complexities were implemented. HyperWorks was used to vary the dimensions of the geometrical factors. For each factor, five variants were studied in each airway model. A well-validated fluid–particle transport model was used to simulate the airflow and particle deposition. The geometrical-factor-induced deposition variations were analyzed using ANOVA to determine the relative influence of each factor on particle deposition in the MT airway. Results showed that the realism of airway models significantly affected the MT deposition, and the USP IP underestimated the realistic model by up to 55%. The glottis area and total airway volume were found to be the two most predominant factors (both p values<0.01). Replacing the USP IP 90° elbow with curved bends significantly reduced the deposition. However, the MT airway curvature in the other three models had insignificant effects. The effect of the oral cavity volume was also found to be insignificant. Results of this study can provide guidance in developing or selecting a representative MT model to replace the conventional USP IP. A realistic glottis area should be retained in future computational and in vitro deposition studies.