Effects of applied spray mass on evaporation rate and deposition distribution of aerosol droplets in the respiratory tract

The study of spray evaporation and deposition in the respiratory airway is crucial for understanding the efficacy of inhaled medications. While numerous factors influence these processes, the effect of applied mass remains an underexplored variable. This paper investigated the relationship between the applied mass of a spray and its evaporation and deposition within the respiratory airway. Experimentally determined spray parameters were implemented as the boundary/initial conditions in an integrated MDI-airway model. Large-eddy simulations (LES) and the chemical species model were implemented to simulate airflow and water vapor transport. The discrete-phase Lagrangian approach and a multicomponent evaporation–condensation model were utilized to track the trajectories and deposition of evaporating droplets. The results showed significant thermohumidity differences in the mouth among the four applied masses considered. Droplets evaporated most quickly upon administration; however, it took 0.9 s for 17 mg sprays to reach their equilibrium and 0.4 s for 0.017 mg sprays, indicating a prevailing influence of droplet evaporation throughout the respiratory tract. Smaller droplets evaporated faster than larger droplets and were more affected by the local thermohumidity and applied mass. The most notable dosimetry differences among different applied masses were observed in the mouth and pulmonary region. The regional DF exhibited a positive relationship with applied mass in the mouth but a negative relationship in the larynx and downstream airways. For all applied masses considered, the count-based dosimetry method overestimated the drug-based DF in the pulmonary region by a factor of 2.70%±0.65%, while the mass-based dosimetry underestimated it by a factor of 0.26%±0.08%.