Purpose: This study investigated the effect of oropharyngeal geometry on inhaled aerosol characteristics via pressurised metered dose inhalers (pMDIs), both with or without spacers. \ud Methods: Seven adult oropharyngeal models with different centreline lengths, total volumes, and degrees of constriction were employed as induction ports for a laser diffraction particle size analyser and cascade impactor. Particle size change over time, mass median aerodynamic diameter (MMAD), average median volume diameter (DV50), inhaled doses, and oropharyngeal depositions (percentage of the nominal dose) for aerosols via suspension and ultrafine pMDIs with or without spacers at 30 l/min airflow were determined. \ud Results: Variations in oropharyngeal geometry caused significant variations in inhaled particle size distributions, doses, oropharyngeal drug depositions, and particle size change over time when pMDIs were used without spacers. However, inhaled aerosol characteristics had marginal variations for the ultrafine pMDI plus large volume spacer (MMAD range: 0.69–0.78 µm, DV50 range: 1.27–1.36 µm, inhaled dose range: 46.46–52.92%). It was found that the amounts of inhaled aerosol particles with aerodynamic size of less than 0.83 µm via pMDIs plus large volume spacer were slightly affected by the oropharyngeal geometry. \ud Conclusion: Inhaling ultrafine aerosols via spacers may reduce the effect of oropharyngeal geometry on inhaled aerosol properties
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