Pathological changes of the lungs after prolonged inhalation of high concentrations of oxygen.

The pathological changes in the lungs of six patients who were treated by an artificial ventilation with a Bird or Bennett type respirator for three days to six months with oxygen concentrations of 24-100% were examined by light microscopy, studies on thick-sections, reconstruction models and vascular casts, and morphometric methods. After prolonged inhalation of high concentrations of oxygen the lungs showed thickening of the alveolar wall, marked deposition of reticulin fibers and fibroblastic proliferation in the alveolar wall, reduction in the number of capillaries, an abnormal configuration of the capillary network and hyperplasia of alveolar lining cells. These lesions are not specific to this condition, and seemed to be less marked than similar lesions in cases of chronic forms of fibrosing alveolitis, chronic interstitial pneumonia, usual interstitial pneumonia and so-called pulmonary fibrosis. Morphometric results confirm these histological observations and show not only the concentrations of oxygen but also the duration of high and pure oxygen inhalation have important roles for these pulmonary lesions. The main reasons for these lesions seemed to be repeated damage to the capillaries and loss of the normal configuration of the capillary network, accompanied by rearrangement and reconstruction of the two types of reticulin fibers.