Finite element modelling of human lung parenchyma in healthy and pathological states

A finite element, porous hyperelastic computational model was developed for the purpose of modelling the pressure-volume relationship in lung parenchyma (the smallest part of the respiratory tree where gaseous exchange occurs, responsible for the vast majority of its volume). The anatomical structure selected for this purpose was the pulmonary acinus: the part of the respiratory tree arising for the end of the conducting airway down to its daughter alveoli. In COMSOL Multiphysics, this was constructed as a perfectly spherical geometry scaled proportionally to represent a 2¹⁵ segment of lung tissue (∼100 mm³ volume) with a central Dirichlet boundary core used to specify the given fluid (air) pressure into and out of the structure as a time-dependent function.

Using adapted reference tracheal pressure values, the key material parameters for a healthy pulmonary acinus were found to be K = 5 kPa and κ₀ = 5×10^-5 m². This model was subjected to simulations of tidal and ‘forced’ breathing, with the latter driving the anticipated proportional volumetric deformation seen in medical literature. Pathological lung tissue changes were attempted via an increase in elasticity (for restrictive disease) and an upscaling of the geometry twinned with a tailoring of permeability (for obstructive disease). The 2D-axisymmetric incarnation of this model was then built as a fully 3D geometry, demonstrating an agreement between the results of both, and upscaled versions of the model were built to include multiple ‘bronchioles’ to compare the pressure-volume responses thereof and attempt the inclusion of a lung-cancer-type ‘tumour’ into the geometry.