Modeling RBC and neutrophil distribution through an anatomically based pulmonary capillary network.

An anatomically based finite element model of the human pulmonary microcirculation has been created and applied to simulating regional variations in blood flow. A geometric mesh of the capillary network over the surface of a single alveolar sac is created using a Voronoi meshing technique. A pressure-flow relationship that describes blood cell transit is implemented in the network. Regional flow is investigated by imposing gravity-dependent transpulmonary and transmural boundary conditions. Comparisons of red and white blood cell transit times in the upper, mid, and lower lung showed physiologically consistent trends of a decreasing average transit time and an increased homogeneity of transit time distributions as a result of increasing average capillary diameter and flow down the height of a vertical lung. The model was found to reproduce experimentally consistent trends in red blood cell transit times and relative blood flows with respect to lung height. This model enables flow properties and cell transit time behavior in the pulmonary microcirculation under varying conditions, for example in different "zones" of the lung, to be explored.