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Figure 18. Proposed model for the pathogenesis of long-standing healed BPD. Schematic 1 represents three normal acini (a, b, c), each supplied by a terminal bronchiole. As shown in schematic 2, during positive-pressure ventilation and oxygen delivery for treatment of surfactant deficiency, hyaline membranes or occlusive debris from necrotizing bronchiolitis (arrow) "protects" acinus a from alveolar septal injury, whereas varying degrees of partial occlusion of the bronchioles to acini b and c permit alveolar septal necrosis from barotrauma-volutrauma and oxygen toxicity. Schematic 3 depicts the phase following resolution of bronchiolar obstruction, in which acinus a hyper-expands and continues to develop new alveoli, acinus b has undergone septal fibrosis and is inhibited from further alveolar development, and acinus c has atrophied. (Illustration by Aletta Ann Frazier, MD, Department of Radiologic Pathology, Armed Forces Institute of Pathology.) (Adapted, with permission, from reference 85.)
