CFD study on deposition pattern of adult oropharyngeal drug particles with inhalation devices using realistic anatomical models under steady-state flow.

With the rising burden of chronic respiratory diseases, inhalation therapy is essential for efficient drug delivery, yet oropharyngeal retention still limits effective lung deposition. Delivery efficiency depends strongly on the inhaler type, the oropharyngeal geometry, and the relative positioning. This study aims to analyze these factors, particularly the angle of inhalation between the device and the airway. Real adult mouth-throat models combined with Breezhaler® and Handihaler® devices were developed. Particle deposition under steady-state inhalation conditions was analyzed using the discrete phase modeling (DPM) method. The two devices exhibit distinct flow behaviors: Handihaler® produces higher resistance and stronger vortices, which increase oral deposition, whereas Breezhaler® maintains a more stable flow field. Oropharyngeal geometry, particularly tongue elevation, drives variations in deposition by enhancing turbulence. Significantly, the relative location and inhaler orientation angle are decisive determinants. A non-parallel incident angle significantly reduces aerodynamic resistance above the tongue and mitigates intense airflow impact, though it may cause localized vortex formation. The analysis indicates that higher values for the relative location factors (L0 and Lm) tend to correspond with lower deposition fractions and deposition densities in the mouth and throat. The Breezhaler® demonstrates lower simulated oropharyngeal deposition compared to the Handihaler® due to lower aerodynamic resistance and a more stable flow field within the evaluated models. Additionally, optimizing the relative location by modifying the inhalation angle could significantly reduce drug losses. These findings suggest that selecting the appropriate device type and controlling its orientation are critical for enhancing targeted pulmonary delivery.