FIGURE 6.

A two-dimensional finite element computational model of interconnected alveolar walls to study the impact of areas of stress-focus (S-F) on stress–strain relationships. Both a hexagonal honeycomb (top) and Voroni honeycombs (bottom) were studied with areas of S-F created by increasing the stiff regions in one (A) or nine (B) cells. These stiff regions simulate collapsed alveoli adjacent to open alveoli that create an S-F in acute respiratory distress syndrome (ARDS) patients (Figure 4) (Cressoni et al., 2014). The entire honeycomb structure was expanded and exposed to strains of 15, 30, 45, and 55% above the resting geometry. Some of the alveolar walls in the Voroni honeycomb were exposed to a S-F ∼16 times greater than that applied to uniformly expanded areas. This suggests that ventilation pressures considered safe in ARDS patients (<30 cm H₂O) (Acute Respiratory Distress Syndrome Network, 2000) could be causing local stress concentration on some alveolar walls of approximately 48 cm H₂O, with even higher stress in areas of S-F (Makiyama et al., 2014). Permissions obtained from Elsevier. License 4699410294890.