Relationships between alveolar size and fibre distribution in a mammalian lung alveolar duct model.

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Abstract
A finite element model, comprising an assemblage of tetrakaidecahedra or truncated octahedra, is used to represent an alveolar duct unit. The dimensions of the elastin and collagen fibre bundles, and the surface tension properties of the air-liquid interfaces, are based on available published data. Changes to the computed static pressure-volume behavior with variation in alveolar dimensions and fibre volume densities are characterized using distensibility indices (K). The air-filled lung distensibility (Ka) decreased with a reduction in the alveolar airspace length dimensions and increased with a reduction of total fibre volume density. The saline-filled lung distensibility (Ks) remained constant with alveolar dimensions and increased with decreasing total fibre volume density. The degree of geometric anisotropy between the duct lumen and alveoli was computed over pressure-volume cycles. To preserve broadly isotropic behavior, parenchyma with smaller alveolar airspace length dimensions required higher concentrations of fibres located in the duct and less in the septa in comparison with parenchyma of larger airspace dimensions.