ELN and pulmonary emphysema: In a rat model of emphysema induced by intratracheal instillation of elastase followed after 4 weeks by analysis of lung mechanical properties and immunostaining, emphysematous lungs were characterized by increased compliance and rupture of collagen fibers under mechanical strain, suggesting that collagen contributes with elastin to normal lung elasticity, and that emphysema is associated with damage to collagen fibers, which appear thicker but weaker than in normal lungs [46].