Effects of MDI spray angle on aerosol penetration efficiency through an oral airway cast

Many parameters affect the penetration efficiency of the metered-dose inhaler (MDI). In this study, we investigate the effect of the MDI spray angle on the aerosol penetration efficiency through a human oral airway. A computer simulation of the fluid flow and the aerosol transport patterns within a three-dimensional human airway model is first conducted to facilitate the understanding of the aerosol deposition mechanisms. The results of the simulation's predictions are then verified by in vitro experiments conducted in the identical oral airway geometry. Expansion balloons are used in the aerosol experiments for generating air flows as well as collecting the penetrated fluorescent particles. Air flow rates of 30, 60, and 90 L/min are examined. Mouthpiece diameters of 16 and 20 mm and aerosol diameter of 7μm are used in the experiments. This study shows that the aerosol entrance angle has a strong effect on the MDI penetration efficiency, particularly at the higher flow rate. Aerosol penetration efficiency increases monotonically from 0∘0∘ to 20∘20∘ degree entrance angle, reaches the maximum value at about 20∘20∘, and then decreases monotonically when the angle further increases. The measured MDI efficiency enhancement ranges between 10% and 194% depending on the mouthpiece diameter and the air flow rate.