Modelling the lung aids in understanding of pulmonary diseases

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High-performance computing is being used to model how air flows through the passageways of the lung. Ching-Long Lin, professor of mechanical and industrial engineering at the University of Iowa and a research engineer at IIHR-Hydroscience and Engineering, is heading the project that aims to better understand questions such as what causes asthma, how exposure to environmental pollutants alter the development of children's lungs, and how the addition of helium to aerosol drugs can make pharmaceuticals more effective.

Lin, along with Eric Hoffman (University of Iowa) and Merryn Tawhai (University of Auckland), conducted computer simulations on Lonestar and Ranger supercomputers at the Texas Advanced Computing Center (TACC). 'Our approach to understanding the airflow and particle transport in the human lungs is quite novel,' Lin said. 'We use computed tomography [CT] images to construct realistic human lung models, and then we use computational fluid dynamics models to simulate the airflow through the lung.'

Lin's algorithms on Lonestar and Ranger simulate up to 23 bifurcations, or generations, of branching airways to create a mesh model of tremendous complexity and usefulness. The largest of these lung branches are centimetres wide; the smallest are measured in millimetres. Since airways at different scales have important, interrelated features, all of them need to be integrated into a multi-scale whole — a feat that had never before been accomplished because of the inherent algorithmic challenges and extreme computational demands.

Lin's contribution to the project, and to multi-scale modelling overall, is a numerical scheme coupling very accurate 3D models of the lungs (generated by the CT scan) with less accurate but more widespread 1D models (derived from computer simulations), combining the best of both worlds and representing how they function together.

The method lets the team determine the boundary conditions at the outlets of the smallest branches with far greater accuracy. This allows researchers to model how air flows through 23 generations of branches, where it becomes turbulent, and where particles are deposited.

'The multi-scale, CFD framework is essential for delivering this technology "to the bedside" because it allows us to select a combination of the 3D and 1D domains to give fine scale computation (3D) in critical areas, and coarse scale computation (1D) in the remainder of the lung,' said Merryn Tawhai, senior research fellow at the Auckland Bioengineering Institute and Lin's collaborator on the project. 'This minimises model size, reduces run time, and makes the process of patient-specific modelling feasible.'