Deposition of micrometer particles in pulmonary airways during inhalation and breath holding

We investigated how breath holding increases the deposition of micrometer particles in pulmonary airways, compared with the deposition during inhalation period. A subject-specific airway model with up to thirteenth generation airways was constructed from multi-slice CT images. Airflow and particle transport were simulated by using GPU computing. Results indicate that breath holding effectively increases the deposition of 5 μm particles for third to sixth generation (G3-G6) airways. After 10 s of breath holding, the particle deposition fraction increased more than 5 times for 5 μm particles. Due to a small terminal velocity, 1 μm particles only showed a 50% increase in the most efficient case. On the other hand, 10 μm particles showed almost complete deposition due to high inertia and high terminal velocity, leading to an increase of 2 times for G3-G6 airways. An effective breath holding time for 5 μm particle deposition in G3-G6 airways was estimated to be 4-6 s, for which the deposition amount reached 75% of the final deposition amount after 10 s of breath holding.