CONGESTIVE ATELECTASIS IN LUNGS OF RABBITS AND OTHER ANIMALS SUBJECTED TO THE ACTION OF LOW BAROMETRIC PRESSURE

1. In rabbits, guinea‐pigs, rats, cats, and a dog subjected to the action of low barometric pressure, congestive lung atelectasis, of varying extent, has been found at post‐mortem examination. 2. Experiments on rabbits exposed to decreased partial pressures of oxygen at different barometric pressures have shown that there is no relation between the incidence of congestive atelectasis and partial pressure of oxygen. The animals dying of anoxia at ground level or at barometric pressures between 500 and 300 mm. Hg showed all the usual lung changes but no congestive atelectasis. 3. The animals decompressed from 3 or 5 atmospheres pressure to ground level also did not exhibit this lung change. There was no relation between the rate of decompression from the normal to low barometric pressures and the incidence or extent of congestive atelectasis. 4. A direct relation between the level of decompression (300‐100 mm. Hg) and the incidence and extent of atelectasis was found, and it was concluded that the absolute rarefaction of air was the prime cause of congestive atelectasis formation. 5. An increase of intra‐pulmonary pressure maintained in animals at low barometric pressures prevented lung atelectasis formation. 6. The results of experiments of Hanson and Sjöstrand on the formation of lung atelectasis under the influence of different factors decreasing lung capacity at ground level are confirmed. 7. The possible mechanism responsible for the lung atelectasis formation under the influence of low barometric pressure is discussed. We are very grateful to Professor I. de Burgh Daly for providing laboratory facilities and for his constant interest and advice. Our thanks are also due to Dr. Catherine Hebb and Dr. W. Missiuro for their help in carrying out some of the experiments. The expenses of this work were partially covered by a grant from the Polish Air Medical Council to J. Fegler.