Aerosol drug delivery in pediatric airways: in vitro and CFD insights into tongue position and inhalation patterns using soft mist inhalers

Respiratory diseases such as asthma have a significant impact on children worldwide, underscoring the need for accurate assessments of aerosol drug delivery. This study integrates computational fluid dynamics (CFD) and in vitro experiments to evaluate drug deposition from a soft mist inhaler (SMI) in a pediatric mouth-throat (MT) airway. Large eddy simulation (LES) and the discrete phase model (DPM) were employed in ANSYS Fluent to investigate the effects of various inhalation profiles and tongue positions on droplet behaviour. The numerical results closely matched in vitro data obtained from a next-generation impactor, with a root mean square error (RMSE) of 0.061. We found that the deposition of aerosol medications in pediatric patients was over twice that of adults at an inhalation flow rate of 30 l/min under normal tongue posture. Lowering the tongue position reduced deposition within the mouth and on the device's mouthpiece, while increasing deposition in the throat and at the outlet. Higher flow rates enhanced the retention of small droplets (0.1-2 μm) and broadened the deposition sites. A predictive correlation for mouth deposition was established for Stokes numbers greater than 0.02. Simulating realistic asthma profiles, along with 2-step and 3-step pulsatile inhalation patterns, enhanced the retention of small droplets and decreased the deposition of larger droplets (ranging from 5 to 60 µm). These conditions contributed to reduced mouth deposition and increased drug loss to the mouthpiece. Notably, pulsatile profiles increased tongue deposition, whereas the asthma profile enhanced deposition on the palate wall.