Resistance to alveolar shape change limits range of force propagation in lung parenchyma

• Two and 3 dimensional computational models of lung parenchyma with adjustable resistance to shear are developed.
• The range of forced propagation into the parenchyma away from an embedded contracting airway is calculated for both models.
• As resistance to shear increases from zero the range of forced propagation rapidly decreases to become similar to the predictions of an elastic continuum.
• We conclude that real lung parenchyma is appropriately modeled as an elastic continuum.

We have recently shown that if the lung parenchyma is modeled in 2 dimensions as a network of springs arranged in a pattern of repeating hexagonal cells, the distortional forces around a contracting airway propagate much further from the airway wall than classic continuum theory predicts. In the present study we tested the hypothesis that this occurs because of the negligible shear modulus of a hexagonal spring network. We simulated the narrowing of an airway embedded in a hexagonal network of elastic alveolar walls when the hexagonal cells of the network offered some resistance to a change in shape. We found that as the forces resisting shape change approach about 10% of the forces resisting length change of an individual spring the range of distortional force propagation in the spring network fell of rapidly as in an elastic continuum. We repeated these investigations in a 3-dimensional spring network composed of space-filling polyhedral cells and found similar results. This suggests that force propagation away from a point of local parenchymal distortion also falls off rapidly in real lung tissue.