Aerosol transport and deposition in a triple bifurcation bronchial airway model with local tumors

Airflow characteristics and particle deposition have been numerically simulated in a triple bifurcation lung airway model (from generation 3-6 airways) with local tumors protruded from the sidewalls of generation 5 airways. The effects of tumors in terms of size and location on airflow, particle transport, and deposition patterns were analyzed for constant inspiratory flow rates with inlet Reynolds (Re-match = 463 and 1882) and Stokes number (St(match) = 0.02-0.12) combinations that match different cyclic inhalation waveforms. The size of tumors was varied to induce an obstruction of airway lumen by 16-74%. Extreme conditions, 2 and 100% obstruction, were also examined. The results show that enhanced deposition occurs in the carina region at each bifurcation, and deposition increases with increasing Stokes and Reynolds number as expected from earlier studies. In addition, deposition increases at the tumor site until the tumor blocks about half of the airway lumen and then decreases with a further obstruction. In other words, there exists a maximum particle deposition fraction (DF) for a protruding tumor that occludes the lumen. The maximum DF at the tumor was 10.2% within the test conditions used. Deposition occurs mainly on the frontal surface of the tumors, but spreads out to the opposite wall, or upstream sections, or sister branches of the tumor at high flow rates and Stokes number. The present results (1) help in the understanding of the complex toxic or therapeutic aerosol dynamics in the lung with local airways obstruction, and (2) provide quantitative information on critical tumor size and particle deposition to health care specialists.