Figure 1 | Scientific Reports

Figure 1

From: Stress–strain curve and elastic behavior of the fibrotic lung with usual interstitial pneumonia pattern during protective mechanical ventilation

Figure 1

(Panel A) geometry of the three-layered shell modeling an alveolus. Dark gray indicates a layer of collagen interposed between two layers composed of elastin and ground substance, colored in light gray. The shell is inflated by an inner pressure \(P.\) The inset shows the stress components acting at each point of the shell material: the radial stress component, \({\sigma }_{r}\), is in the radial direction, and the circumferential (or hoop) stress components, \({\sigma }_{\theta }\) and \({\sigma }_{\varphi }\) (here \({\sigma }_{\varphi }={\sigma }_{\theta },\) due to axial symmetry), are in the tangential direction of the meridians and the parallels of the sphere. (Panel B) For a homogeneous shell, force equilibrium requires the resultant of \({\sigma }_{\theta },\) acting on the small area depicted in gray, to be much larger than the resultant of the pressure \(P\) acting on the dashed larger area.

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