Multiple wall in-folds sub-divide single segments during capillary regression in hyperoxic acute lung injury

The present study provides further insight into the structural processes that remodel pulmonary capillaries in the injured adult lung. Early in hyperoxia acute lung injury (HALI), many sub-dividing segments are present throughout the capillary network before segment occlusion and loss predominate and capillary density decreases later in the period. A second segment sub-division triggered in regenerating capillaries after air breathing (post-HALI) demonstrates a similar mechanism of organization at a time of contrasting change in the capillary density. As we have previously reported, the process of segment sub-division includes in-folding of the endothelial-epithelial surface (alveolar-capillary membrane) to form inter-luminal structures (ILSs) and loops, with loop separation increasing segment number. Unexpectedly, the findings support remodeling of the capillary density by wall in-folding in acute lung injury, demonstrating a similar mechanism in capillary regression as well as in regeneration in the adult lung.