Fig. 2.

A: schematic representation of a series of spring-string pairs representing a strip of lung parenchymal tissue. The extensible springs (springs constants k₁, k₂, etc.) represent elastin fibers, while the inextensible strings (lengths l₁, l₂, etc.) represent collagen fibers. [Reproduced with permission from Ref. 37.] B: 2-dimensional network model of lung parenchymal tissue at various stages of stretch. Each line element represents a spring with a highly nonlinear stress-strain relationship. The black rectangles show the resting tissue shape. The numbers in the margin are total force. Note how a percolating series of contiguous links with high stress appears as strain increases. [Reproduced with permission from Ref. 38.]