ELECTRON MICROSCOPIC AND MORPHOMETRIC STUDY OF RAT LUNGS EXPOSED TO 97% OXYGEN AT 258 TORR (27,000 FEET).

A group of young growing rats was exposed to 97 oxygen at 258 torr in a controlled environmental chamber. They were sacrified in groups after 1, 5, and 14 days and their lungs were processed for morphometric examination in light and electron microscope according to standardized procedures. No qualitative pathologic changes in lung structure were found even after 2 weeks of oxygen exposure. Only one exception was an apparent increase in the number of eosinophilic granulocytes within the lung capillaries of test rats which had been exposed to pure oxygen for 5 and 14 days. In the test animals a fall in lung volume and in lung-volume-to-body-weight ratio was concurrent with impairment of body growth. Morphometric analysis revealed a statistically highly significant decrease in alveolar surface area, capillary surface area, and volume in dependence of the duration of oxygen exposure. These changes are interpreted as oxygen effect which, however cannot be called oxygen toxicity proper. Rather they are regarded as adaptation of the growing organism to increased oxygen tension in the breathing medium. Author