Fig. 1
From: Ventilatory support and mechanical properties of the fibrotic lung acting as a “squishy ball”
Relationship between stress and strain in healthy, ARDS and fibrotic lungs. The specific elastance (K) is the slope of the curve in its linear portion. Although ARDS lungs are characterized by low compliance, its elastic properties follow those of healthy lungs provided that the deformation induced by tidal ventilation is normalized to the end-expiratory lung volume. In ARDS, the “baby lung” (gray area) inflates until a certain level where hyperinflation occurs and the linearity of the stress–strain relation is lost, approaching the breakdown limit of the extracellular matrix constituents (lightning). In fibrotic lungs, the specific elastance is higher thus the stress–strain curve is steeper. During inflation, the healthy regions protrude through the fibrotic walls, as illustrated by the hand progressively squeezing the “squishy ball”. Compared to ARDS, the breakdown is reached at lower stress and lower strain. ARDS acute respiratory distress syndrome, VT tidal volume, EELV end-expiratory lung volume, PL transpulmonary pressure