Effects of vocal fold adduction on the particle deposition in the glottis: A numerical analysis and in vitro assessment

Background: The efficacy of inhalation therapy depends on the drug deposition in the human respiratory tract. This study investigates the effects of vocal fold adduction on the particle deposition in the glottis.Methods: A realistic mouth-throat (MT) geometry was built based on CT images of a healthy adult (MT-A). Mild (MT-B) and great (MT-C) vocal fold (VF) adduction were incorporated in the original model. Monodisperse particles range in size from 3 to 12 mu m were simulated at inspiration flow rates of 15, 30 and 45 L per minute (LPM). The regional deposition of drug aerosols was performed in 3D-printed models and quantified using highperformance liquid chromatography.Results: Both the numerical analysis and in vitro experiments show that most particles are deposited in the mouth, pharynx and supraglottis, while few are deposited in the glottis and subglottis. For most cases in MT-A, the particle quantity in glottis is lower than 0.02 N/mm2 at 15 and 30 LPM while they increase dramatically at 45 LPM. It peaked at 0.347 N/mm2 for 5-mu m particles at 45 LPM in MT-B and 2.324 N/mm2 for 6-mu m particles at 30 LPM in MT-C. The lowest drug mass faction in the glottis in vitro were found at 15 LPM for MT-A and MT-C, and at 30 LPM for MT-B, whereas it peaked at 45 LPM for all MT models, 0.71% in MT-A, 1.16% in MT-B, and 2.53% in MT-C, respectively.Conclusion: Based on the results of this study, larger particles are more likely to be deposited in the oral cavity, oropharynx, and supraglottis than in the glottis. However, particle deposition in the glottis generally increases with VF adduction and greater inspiratory flow rates.