704 PHYSIOLOGY OF RESPIRATION. 



High and Low Barometric Pressures, Mountain Sickness. 

 Caisson Disease, etc. — High barometric pressures are used m 

 submarine work, diving, caisson work, etc. As stated above, it 

 follows from the work of Bert and Smith that when the pressure 

 reaches 5 to 6 atmospheres long continuance in it may be followed 

 by injurious or fatal results due to the toxic action of the oxj^gen. 

 If the pressure is increased to 15 atmospheres the toxic influence 

 of the oxygen brings on death with convulsions. Practically, 

 however, such pressures are not encountered in submarine work. 

 A caisson is a wooden or steel chamber arranged so that it may 

 be sunk under water. The water is driven out by air under pres- 

 sure. Since the pressure increases 1 atmosphere for each 10 

 meters (33 feet), it will be seen that very high pressures of air 

 are not usually required. Caisson workers are at times attacked 

 by serious or even fatal symptoms, not while in the compressed 

 air, but during or after the "decompression" that is necessary in 

 the return to normal conditions. The symptoms consist of pains 

 in the muscles and joints, paralysis, dyspnea, congestion. Those 

 who have investigated the subject* state that the injurious results 

 are due to a too rapid decompression. When this occurs the gases 

 in the blood, particularly the nitrogen, are suddenly liberated as 

 bubbles, which block the capillaries and thus produce anemia in 

 different organs. If the decompression is effected gradually no evil 

 results follow. 



The effect of low barometric pressures is chiefly of interest in 

 connection with residence in high altitudes and aviation. At 

 certain altitudes, from 3000 to 4000 meters, disagreeable symp- 

 toms are experienced by many persons, especially after mus- 

 cular effort, which are designated usually under the term "moun- 

 tain sickness." The individual so affected suffers from head- 

 ache, nausea, vertigo, great weakness, etc. Much investigation, 

 especially of recent years, has been devoted to this subject. f Paul 

 Bert concluded, from Ms numerous experiments, that a fall in baro- 

 metric pressure acts upon the organism only in so far as there is a 

 diminution of the partial pressure of the oxygen in the air respired. 

 This view has been generally accepted in physiology, and mountain 

 sickness and similar disturbances in balloon ascents have been 

 explained, therefore, as due mainly to the lack of oxygen, — that is, 

 to the condition of anoxemia. Mosso, on the contrary, has insisted 

 upon the part played by the carbon dioxid. He gives experi- 



* See Bert, loc. cit., p. 939; also Hill and MacLeod, "Journal of Physi- 

 ology," 29, 382, and "Journal of Hygiene," 3, 407. 



t See "Zunts et al. Hohenklima u. Bergwanderungen in ihrer Wirkung 

 auf d. Menschen," Berlin, 1906. Mosso and Morro, "Archives itaUennes de 

 biologie," 39, 387, also vols. 40 and 41. Douglas et al, "Physiological Observa- 

 tions made on Pike's Peak," etc.; "Philosophical Trans.," London, B. 203. 

 185, 1913. 



