Multi-scale models of the lung airways and vascular system

Medical imaging now enables measurement of the lung in vivo at controlled volumes, prompting the development of increasingly sophisticated models of the geometry of the lung, from the largest airways and vessels to the alveolar tissue and capillary bed. We have developed methods for deriving subject-specific models of the airway and pulmonary vascular trees and have developed methods to represent the structure of alveolated parenchymal tissue and the segmented alveolocapillary network. These multi-scale models have geometry that is consistent with published lung morphometry and have defined relationships with one another. The models can therefore be readily exploited to couple multiple processes at the same physical scale (e.g., tissue mechanics and blood flow), or to couple over multiple scales (e.g., Newtonian flow in the large elastic blood vessels, and two-phase fluid transit in the microcirculation). We have studied function in the peripheral pulmonary system (alveolated airways and accompanying arterial and venous vessels) using a multi-scale approach that integrates detailed structure at this level of interest with estimates of air, blood and tissue pressures from functional models in the larger airways and vessels and simulations of soft tissue deformation of the whole lung. This approach allows us to study how ventilation of the acinus, mixing of inert gases and perfusion of the capillary bed varies with gravity, location in the lung and posture. An extension of the multi-scale models is incorporation of respiratory gas exchange, which can also be considered at several scales of interest.