In vitro inhalation and deposition of salbutamol in upper airway geometries

Purpose: 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.

Methods: 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 ® ).

Results: 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.

Conclusions: 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.