Effects of Airway Generation Depth on Particle Deposition Behaviour in the Main Respiratory Airways—A Computational Modelling Study

PURPOSE: Effective inhaled drug delivery depends on formulation, device, and a clear understanding of aerosol transport in the respiratory tract. This study explores how lower airway anatomical complexity affects airflow and particle deposition in the main respiratory airways. METHODS: Seven 3D bronchial models with varying airway generational depths were developed. Numerical simulations were conducted using the discrete phase model (DPM) to simulate aerosol transport and deposition under transient inspiratory flows at inhalation peak flow rates of 60 and 120 L/min. RESULTS: Our results showed that simplified models with three bronchial generations could underestimate the deposition efficiency in the main respiratory airways by up to 65.6% compared to the seven-generation lower airway model. Additionally, disparities in deposition outcomes and flow characteristics diminished with increasing lower airway complexity, with minimal changes in flow dynamics and deposition observed beyond the model with six bronchial generation. CONCLUSIONS: This study suggests that airway models incorporating at least up to the 6th generation of bronchial branching may be required to sufficiently capture the implications for inhalation therapy design and the development of reliable in silico testing frameworks. Notably, insufficient lower airway detail not only compromises lung deposition estimates but also affects airflow dynamics throughout the entire respiratory tract, including the upper airway. This study highlights the importance of retaining detailed geometry in the design of inhalation therapies and the development of in silico testing frameworks.