Deposition of inhaled micrometer-sized particles in oropharyngeal airway replicas of children at constant flow rates

This study is aimed at quantifying the deposition of micrometer-sized aerosols in realistic oropharyngeal airway replicas of children 6–14 years old, as well as minimizing interindividual scatter in correlations that fit this data. To perform this study, computed tomography (CT) images of nine children were taken during inhalation at a constant flow rate delivered by an AKITA® inhalation system. After segmenting the oral airways from the CT scan images, rapid prototyping technology was employed to fabricate plastic replicas of the airways. Deposition was then measured by comparing the number concentration of jojoba oil particles, generated by a six-jet Collison atomizer, passing through the replica vs. a blank line with no replica attached. The number concentration and the size of particles in 6 size ranges in the aerodynamic size range of 0.5–5.3 μm associated with the impactor stage cutpoints were measured using an electrical low pressure impactor (ELPI). Five medium to high constant breathing flow rates, ranging from 30 to 150 L/min, were generated using two vacuum pumps in series. Prior to testing the childrenʹs replicas, our deposition measurements were validated using a well-characterized and commercially-available geometry, the Alberta Idealized Throat. The replicas were re-scanned with CT to ensure a high quality fabrication and to measure their dimensions. These dimensions were used to establish a non-dimensional correlation, consisting of Stokes and Reynolds numbers, to reduce the scatter in deposition. Our proposed correlation may be useful for the prediction of deposition of micrometer-sized particles in the oropharyngeal airways of children during inhalation at moderate to high constant flow rates, typical of that seen during the use of pharmaceutical aerosol inhalers.