The effects of aerosol concentration on the evolution, transport, and deposition of hygroscopic droplets in the highly idealized MT model: A numerical study

Inhalation therapy is widely used to treat various respiratory diseases. Nebulizers have been widely adopted due to their ease of operation, high drug delivery efficiency, and low residual volume. Traditional studies on drug delivery in the respiratory tract typically use a one-way coupled method to track drug transport and deposition for non-hygroscopic drug particles. However, neglecting the concentration of nebulized hygroscopic droplet aerosols can lead to significant discrepancies in the deposition efficiency (DE) of nebulized drugs in the airways. To investigate the effect of different nebulization rates on the evolution, transport, and deposition of droplets, a highly idealized mouth-throat (MT) model was selected as a testbed for the in silico trials of drug delivery to the respiratory tract. The interaction between continuous and discrete phases was modeled using a two-way coupled model of highly concentrated droplet aerosol-water vapor interaction, innovated by the particle parcel method. The effects of different coupling methods and boundary conditions on the average droplet diameter and droplet deposition distribution pattern at the outlet of the MT model were compared using a computational fluid dynamics (CFD) method. Simulation results indicate that neglecting the effect of water vapor evaporated from the droplets on the relative humidity (RH) in the oral cavity could lead to a 2.2-fold prediction error of the average droplet diameter at the outlet of the MT model for a conventional nebulization rate of 0.386 g/min. As the nebulization rate increases, the difference in the predicted average droplet diameter at the outlet of the MT model between the one-way coupled method and the two-way coupled method also increases. Increasing the nebulization rate during inhalation therapy could lead to incomplete evaporation of drug droplets, resulting in deposition of larger diameter drug droplets in the oral cavity. In contrast, a lower nebulization rate can reduce the droplet diameter at the outlet of the MT model, allowing it to enter deeper airways.

Automated summary

Inhalation therapy is a common method for treating respiratory diseases, and nebulizers are widely used due to their convenience, high drug delivery efficiency, and low residual volume. However, traditional studies on drug delivery have focused mainly on non-hygroscopic drug particles, neglecting the concentration of nebulized hygroscopic droplet aerosols, which can significantly affect drug deposition efficiency.