Regional Deposition of Particles in an Image-Based Airway Model: Large-Eddy Simulation and Left-Right Lung Ventilation Asymmetry

Abstract

Regional deposition and ventilation of particles by generation, lobe and lung during steady inhalation in a computed tomography (CT) based human airway model are investigated numerically. The airway model consists of a seven-generation human airway tree, with oral cavity, pharynx, and larynx. The turbulent flow in the upper respiratory tract is simulated by large-eddy simulation. The flow boundary conditions at the peripheral airways are derived from CT images at two lung volumes to produce physiologically realistic regional ventilation. Particles with diameters equal to or greater than 2.5 microns are selected for study because smaller particles tend to penetrate to the more distal parts of the lung. The current generational particle deposition efficiencies agree well with existing measurement data. Generational deposition efficiencies exhibit similar dependence on particle Stokes number regardless of generation, whereas deposition and ventilation efficiencies vary by lobe and lung, depending on airway morphology and airflow ventilation. In particular, regardless of particle size, the left lung receives a greater proportion of the particle bolus as compared to the right lung in spite of greater flow ventilation to the right lung. This observation is supported by the left-right lung asymmetry of particle ventilation observed in medical imaging. It is found that the particle-laden turbulent laryngeal jet flow, coupled with the unique geometrical features of the airway, causes a disproportionate amount of particles to enter the left lung.

Acknowledgments

This work was supported in part by NIH-R01-EB-005823, NIH-R01-HL-064368, NIH-R01-HL094315, NIH-S10-RR-022421, a University of Iowa CTSA NIH/NCRR grant 1UL1RR024979 and a NIEHS/NIH Center Grant P30 ES05605. The authors would also like to thank Jiwoong Choi, Haribalan Kumar, and Youbing Yin for assistance during the course of the study, and thank Drs. Yue Zhou and Yung-Sung Cheng at the Lovelace Respiratory Research Institute for providing their experimental data (Zhou and Cheng 2005). The computer time was supported by TeraGrid TACC.