O₂- and pneumonia-induced lung injury. I. Pathological and morphometric studies

The physiological, morphological, and morphometric findings of several lung injury models in baboons have been compared in the following six study groups: 1) initial injury with oleic acid followed by ventilation with 100% O₂, 2) ventilation with 100% O₂, 3) ventilation with 80% O₂, 4) ventilation with 80% O₂ followed by inoculation of Pseudomonas aeruginosa, 5) ventilation with 40% O₂, and 6) normal nonventilated room-air-breathing animals. The animals were maintained for 11 days in an intensive care unit. Light microscopically, animals ventilated with 40 and 80% O₂ showed mild lung injury, consisting mostly of an increase in alveolar macrophages in peribronchiolar sites and focal alveolar wall widening. The 100% O₂-oleic acid, 100% O₂, and 80% O₂-Pseudomonas-treated baboons showed mixed exudative-reparative diffuse alveolar lesions. Ultrastructurally, the type II cells of these three groups had significantly altered morphology with aberrations of lamellar body configurations. Morphometric findings showed increases in type II and interstitial cells and decreases in type I and endothelial cells in these injured animals. A striking finding was that the physiological, morphological, and morphometric changes of an 80% O₂-Pseudomonas insult was as injurious as 100% O₂. This synergistic effect of hyperoxia and infection very likely reflects the most frequent evolution of adult respiratory distress syndrome in patients in intensive care units.