Impact of COPD breathing profile and airflow relative humidity on drug delivery in mouth–throat airway through pMDIs: In vitro and CFD studies

This study examined key factors influencing drug delivery from pressurized metered-dose inhalers (pMDIs), focusing on constant versus chronic obstructive pulmonary disease (COPD) breathing profiles and varying relative humidity (RH) conditions. A combined experimental and numerical approach was employed using an eight-stage next generation impactor (NGI) along with computational fluid dynamics (CFD) simulations. The simulations incorporated a low Reynolds number (LRN) k–ω turbulence model and a discrete phase model (DPM) to evaluate particle size distribution and deposition within the mouth–throat airway geometry. At a low flow rate of 30 L/min, the mass fraction of large particles (12–15 μm) deposited on airway walls increased by 39% compared to that at a flow rate of 60 L/min. The CFD analysis identified two significant recirculation zones near the bend between the mouth and throat, which notably affected deposition patterns. Additionally, relative humidity was found to influence deposition efficiency. At 99% RH, a higher number of large particles (> 10 μm) passed through the airway outlet, resulting in reduced deposition in the upper airway. Under COPD breathing conditions, delayed spray development contributed to increased deposition of large particles on airway surfaces. However, in areas of high turbulence, especially under elevated humidity, there was a reduction of approximately 4% in the mass fraction of large particles deposited on the walls.