CHAPTER XLVI 



THE PHYSIOLOGY OF BREATHING IN COMPRESSED AIR AND 



IN RAREFIED AIR 



In the application of a knowledge of the physiology of respiration to 

 the investigation of disease, a group of conditions arises in which con- 

 siderable interference with physiologic mechanisms occurs, not as a result 

 of disease, but of changes in the atmospheric environment. The regula- 

 tion of the functions of respiration depends very largely on changes in 

 the physical and chemical properties of the alveolar air, so that it is to 

 be expected that similar changes in the atmosphere will have a marked 

 influence on the respiratory activity and on the general well-being of 

 the animal. 



The most thoroughly investigated of these conditions are those which 

 develop in rarefied and compressed air. Either condition can be pro- 

 duced experimentally in the laboratory by the use of air-tight chambers 

 (pneumatic cabinets) and suitable pumps, although most of the im- 

 portant work on the effects of rarefied air has been conducted at high 

 altitudes, where the barometric pressure is low. 



MOUNTAIN SICKNESS 



This condition depends primarily on disturbances in the control of the 

 respiratory function, and it is on account of the useful information con- 

 cerning the nature of these functions, rather than because of the so-called 

 disease itself, that so much attention has been devoted to its investiga- 

 tion during recent years. The disturbances produced by the rarefied 

 atmosphere develop rather quickly, but after some time they gradually 

 disappear, indicating that the organism has acclimated itself that is, 

 the compensatory mechanisms have come into play to bring the respira- 

 tory control back to normal. When animals are placed in pneumatic 

 cabinets from which some of the air is pumped out, most of the imme- 

 diate symptoms observed in mountain sickness occur, but it is usually 

 impracticable to continue the observations for a sufficient length of 

 time to allow the compensating mechanisms to develop. 



Because of their great value in revealing the nature of the respiratory 

 hormone, many of the results of the recent investigations on mountain 



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