Capillary structure in elastase-induced emphysema.

The essential component of pulmonary emphysema is destruction of alveoli. Because capillaries make up much of the alveolar wall, it has been a long-held opinion that capillary loss in this disease parallels the loss of other elements of the alveolar septum. Yet the nature of the damage to capillaries and the occurrence of microvascular remodeling are unknown. Scanning electron microscopy of vascular casts of lungs from rats given intratracheal elastase were studied for identifying capillary changes in this type of experimental emphysema. The pressure-volume curves showed a clear distinction between the elastase and saline control animals, and light microscopy showed alveolar enlargement consistent with mild emphysema. The casts of capillaries in the elastase lungs appeared to have larger alveolar baskets, and capillaries ended abruptly near areas of focally destroyed lung. The elastase animals had more nonconnecting capillary segments on the pleural surface where the emphysema was worse and folds in the capillaries were more pronounced, suggesting weakened alveolar walls. The capillary density was decreased on the pleural surface, although this decrease could have resulted from hyperinflation. No difference in capillary diameters or branching frequency occurred. It appears that in this model of emphysema, decreased elastic recoil occurs before diffuse loss of capillaries.