Deposition of ultrafine particles at carinal ridges of the upper bronchial airways

Bifurcations of the upper bronchial airways are primary hot spots for deposition of inhaled particles and noxious gases. Deposition of coarse particles in the carinal ridges results from inertial impaction, and deposition distal to these sites is attributed to secondary flows. Diffusional deposition of ultrafine particles on carinae surfaces is studied here. Similarity solutions for both the flow and concentration fields at the respective boundary layers that develop near the surface of a wedge are presented, corresponding to a relatively high Re number. The expressions developed for the deposition efficiency compare favorably to those obtained by rigorous computational fluid dynamics simulations. Yet unlike simulation-derived expressions that pertain to the specific geometry and flow conditions studied, our expressions are robust and can account for different branching angles, airflow rates, and particle sizes. The average diffusive flux toward the carina walls is in good agreement with experimental deposition data, as well as with simulation results specifically designed to account for deposition hot spots at airway bifurcations. The expressions obtained can be easily implemented in algebraic inhalation dosimetry models to estimate deposition profiles along the whole respiratory system.