Injury and remodeling of pulmonary veins by high oxygen. A morphometric study.

Breathing 87% oxygen at normobaric pressure for 28 days injuries and remodels the wall of distal pulmonary veins (less than or equal to 150 mu). Occluded vessels are evident, as are vessel remnants in which wall integrity is lost (obliterated vessels). Significantly more veins have a muscular or partially muscular wall than normal (P less than or equal to 0.001 for veins in each size category less than or equal to 150 mu, chi-square test). In some veins new muscle develops between an external and internal lamina but in many it develops within the intima, beneath the endothelium and adluminal to a single lamina. Small veins (20-25 mu in ED) with a muscular or partially muscular wall are present only in the hyperoxic lung. Increase in the percent medial thickness (%MT) of veins indicates lumen narrowing: this is relatively greater in the smallest veins. Reduction in the cross-sectional area of venous segments that are immediately postcapillary, by lumen narrowing or occlusion, contributes to the restriction of the pulmonary vascular bed by hyperoxia.