CHAPTER XLVI 



THE PHYSIOLOGY OF. BREATHING IN RAREFIED AND COM- 

 PRESSED 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 physiological 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. 



Man subjects himself to the influence of these conditions by living 

 at high altitudes and by work in caissons and diving suits. Although it 

 has been necessary, in explaining the functions of the respiratory center, 

 to refer in previous chapters to the influence of deficiency of oxygen, 

 it is important that w r e pay some attention to the subject of mountain 

 sickness as a whole, because of the more lasting physiological alterations 

 which become established during it. We will then consider the opposite 

 condition of caisson sickness or diver's palsy. 



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. Tho 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. 



More or less hyperpnea, especially on exertion, soon appears in a 



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