Soft‐mist inhaler spray dynamics and laryngeal deposition in upper airway models

Background: Targeted laryngeal drug delivery is clinically valuable for procedures requiring rapid topical anesthesia. This study evaluated how the mist from a soft-mist inhaler (Softbreezer) interacts with realistic upper-airway anatomy to influence lidocaine deposition. Research design and methods: An in vitro experimental setup was used to assess deposition from the soft mist inhaler across four upper-airway geometries: two simplified models and two subject-specific models. Each model was tested at inhalation flow rates of 15 and 30 L min⁻¹. Deposition was quantified across five anatomical regions. High-speed imaging (6100 fps, 20 μs exposure) characterized plume velocity and cone angle. Results: Droplet size distributions were consistent across flow rates (Dv (Formula presented.) 16 μm). The subject-specific realistic oral inhalation model achieved the highest laryngeal deposition at 5.3% of the delivered dose at 30 L min⁻¹, compared with 2.1% in the simplified Virginia Commonwealth University model and 1.6% in the subject-specific artificially opened mouth model. The United States Pharmacopoeia model underestimated upper-airway deposition. High-speed imaging confirmed a slow, coherent plume with minimal turbulence. Conclusions: Physiologically realistic airway geometry captured during oral inhalation should more accurately represent the flow transitions governing laryngeal deposition.