In Vitro Inhalation and Deposition of Salbutamol in Upper Airway Geometries

Accurate prediction of aerosol deposition in the extrathoracic airway is critical for designing inhaled therapies, yet many experimental and computational studies rely on geometries that are either simplified or subject-specific but not necessarily physiologically consistent with oral inhalation. This inconsistency can lead to varying estimates of drug delivery efficiency, particularly in the mouth-throat region where flow behavior and particle deposition are highly sensitive to physiological detail.

This study investigated the influence of airway geometry on aerosol drug delivery by quantifying the deposition of salbutamol sulfate across simplified and subject-specific extrathoracic models. An artificially opened mouth, derived from a closed mouth CT scan and a realistic oral inhalation geometry, were compared to a simplified airway model and the pharmaceutical standard model. All experiments were performed at an inhalation flow rate of 30 l min $_{}^{-1}$ using a metered dose inhaler (Ventolin $_{}^{\circledR }$ ).

Each airway was segmented into 10 regions, from the device mouthpiece through the mouth-throat, larynx, and trachea, to the eight stages representing the lower airway. The artificial open mouth geometry produced the lowest ling deposition only 9% , while the realistic oral inhalation had lung deposition of 45%, more consistent with the simplified models.

Subject-specific airway models are not inherently more realistic than simplified models. When physiological features of oral inhalation-specifically soft palate elevation and a smaller mouth opening than a fully opened mouth-are not captured in the model geometry, simplified geometries based on oral inhalation conditions may more accurately represent true deposition patterns than subject-specific models derived from restful breathing CT scans.