Potential effects of inhaler mouthpiece size on particle deposition in the human airway

This research aims to improve understanding of the impact of inhaler mouthpiece sizes on particle transport and deposition in the human upper airway. The above is important to optimize inhaler designs and improve inhaled drug delivery's therapeutic efficacy. MRI scans of two healthy human volunteers using a small and a large inhaler mouthpiece mockup were acquired, and this yielded 4 sets of images. Four 3D models of the pharynx were reconstructed from the MR images. CFD simulations using discrete phase modelling and polydisperse particles (MMD: 6.96 μm, span: 1.38 μm) were performed using two different transient flow profiles with different peak flow rates (27 L/min and 85 L/min), resulting in a total of 4 cases (small inhaler – 27 L/min, small inhaler – 85 L/min, large inhaler – 27 L/min, large inhaler – 85 L/min) for each subject. Particles deposition at different regions of the airway models was studied. The results from this research thesis showed that particle deposition in the pharynx associated with a large mouthpiece and low peak flow rate (27 L/min) is more than 80% in one of the subjects, which is onefold higher compared to when the same subject was with the small inhaler mouthpiece. The cases with a small inhaler mouthpiece and high peak flow rate (85 L/min) have the least number of particles deposited in the upper airways of both subjects. The use of a large inhaler mouthpiece results in erratic distribution of particles deposition, with a higher concentration of particles in the oral cavity, not observed with the small inhaler mouthpiece. The results from this work provide further evidence to existing literature that inhaler mouthpiece size matters and that it produces intra and inter-individual variations in drug particle deposition in the human upper airway.