Nasal spray drug delivery beyond the nasal valve: Evidence for the importance of particle-wall interactions and post-deposition liquid motion

The nasal valve is a major barrier to nasal spray drug delivery to posterior structures such as the turbinates, paranasal sinuses, and olfactory region. Geometric considerations predict that the nasal spray dose that reaches the posterior nose is greater in subjects with larger nasal valve cross-sectional areas. Our analysis of the experimental data from Esmaeili et al. (2024) [Journal of Aerosol Science 179, 106387] reveals a paradoxical negative correlation between posterior dose and nasal valve area in pediatric nasal cavities. We hypothesize that the discrepancy between the theoretical prediction of the geometric model and experimental observation is due to the assumption in the geometric model that droplets are trapped and remain at the location where they hit the wall. A calculation of the Weber number suggests that nasal spray droplets >120 μm splash upon collision with the nasal walls, leading to the formation of smaller droplets that can be carried by airflow beyond the nasal valve. A study by Inthavong et al. (2015) suggests that 45 % of the spray mass is composed of droplets ≥120 μm at a distance of 0.6–1.2 cm from the nozzle tip, potentially leading to substantial splashing on the walls of the nasal vestibule. Traditionally, computational fluid dynamics models of nasal spray drug delivery have assumed a trap (stick) boundary condition and have not considered particle-wall interactions or post-deposition liquid motion. This study reviews the evidence that particle-wall interactions and post-deposition liquid motion may play a significant role in determining the regional doses of nasal sprays.