Determinants of mechanical properties of rat lung during postnatal development

We studied the volume-pressure curve of saline-filled lungs in rats between 4 and 40 days of age and correlated measurements of lung mechanical properties derived from these curves, e.g., lung volume at 10 cmH2O (V10), lung elastic recoil, the pressure required to rupture the lung (PRP), and hysteresis ratio (HR) with total lung collagen and elastin. Postnatal lung growth in the rat can be divided into four stages: lung expansion (between birth and 4 days); alveolar proliferation (between 4 and 12 days); elastin accumulation (between 12 and 20 days); and equilibrated growth (between 20 and 40 days). During lung expansion the lung contains little collagen or elastin, has small volumes, low elastic recoil, low PRP, and high HR. During alveolar proliferation lung volumes increase and HR falls, but elastic recoil and PRP do not change. During elastin accumulation lung elastin increases 297% and elastin concentration increases 261%, elastic recoil more than doubles reaching adult levels, and stress relaxation reaches adult values. During equilibrated growth lung elastin and V10/g lung weight plateau, but lung collagen increases 34.3% and collagen concentration doubles as does the structural integrity of the lung as measured by PRP. These studies illustrate the distinct effects of collagen and elastin on lung mechanical properties and define the mechanical consequences of the structural events associated with postnatal lung growth.