Abstract:
To study the ventilation distribution within a human lung a model has been produced that couples soft tissue mechanics and a simplified airflow solution. The model takes account of the regional changes in the material properties of the lung which affect the pressures developed by the lung tissue during ventilation and determine the patency of the airways. The lung geometry was constructed using CT scanned data as far as the 9 th generation. Further airways are grown within the CT-based tissue lobes using a volume filling algorithm. Equations for large deformation elasticity are used to compute regional tissue pressures and a pseudo-elastic strain energy function defines the stress-strain behavior of the lung tissue. These pressures are used in the relationship between pressure and airway radius and as regional alveolar pressures that act as boundary conditions for the flow solution. Initial studies compared the flow component of the model with symmetrical, Horsfield and anatomical (physically realistic) airway geometries to investigate the influence that branching geometry and dimensional asymmetry has on the air flow distribution. The coupled model is used to compare flow distribution and flow-volume loops in a normal human lung undergoing quiet breathing while exposed to different gravities and in different orientations. Results from the isolated flow model and the fully coupled system demonstrate consistency with earlier symmetrical models and with physiological measurements. However, the accuracy of the predictions is sensitive to the accuracy of the strain energy function used for the lung tissue elasticity.
