CLIMATE 909 



The respiratory response to altitude is ordinarily the first of the several 

 compensatory changes to appear. Miss Fitzgerald found that the breath- 

 ing of persons living permanently at an altitude of 2,200 feet, as indicated 

 hy the alveolar carbon dioxid, snowed a larger lung ventilation than under 

 similar conditions at sea level; and further established the law that 

 approximately a 10 per cent increase in the ventilation occurred for each 

 100 m'm. of diminution of the barometric pressure. The full extent of 

 the change in breathing is reached in from 7 to 14: days. 



The type of breathing that is best suited to the need of the body at 

 high altitudes is slow and deep rather than rapid and shallow. After 

 adaptation the depth rather than the rate of breathing will ordinarily have 

 increased. However, during vigorous physical exertion, where even at 

 sea level the depth of breathing is about maximal, at a high altitude 

 such as Pikes Peak the rate shows a marked increase. A subject, who 

 had breathed when in bed at sea level at the rate of 16.8 breaths per 

 minute, on Pikes Peak had a rate of -only 17.3; while walking, at the 

 rate of 5 miles per hour at sea level, the rate was- 20, and on Pikes Peak 

 36 breaths per minute. 



The increased breathing augments the alveolar oxygen tension in the 

 lungs. If, for example, on Pikes Peak, with a barometric pressure of 

 457 mm., the respiration did not change, then the alveolar oxygen tension 

 in the dry alveolar air would fall proportionately with the barometer to 

 about 36 mm. The increase in breathing, however, raises this at that 

 altitude to about 52 mm. As a result the blood will be just that much 

 more saturated with oxygen, thus remedying to some extent the defective 

 saturation of the arterial blood with oxygen. 



The explanation of the manner in which respiration is modified has 

 recently been more fully elucidated. The hormone of breathing is the 

 hydrogen ion concentration in the blood, and not the total carbon dioxid 

 in the blood, nor the concentration of HCO 3 ions as has sometimes been 

 claimed. Haldane(^) has pointed out that the IT-ion concentration of the 

 blood is regulated with great delicacy by the respiration on the one hand 

 and the kidneys and liver on the other. The respiration doing the rough 

 and immediate work by increasing or decreasing the elimination of the 

 carbon dioxid, and the kidneys the finer and slower work. When a person 

 goes to a high altitude the want of oxygen acts as an additional stimulus 

 to the respiratory center with the result that an excess of carbon dioxid 

 is eliminated. This decreases the H-ions and causes a state of alkalosis 

 in the blood. To offset the excess of alkali the kidneys and liver attempt 

 to redress the balance. It has been shown by Haldane, Kallas, and Kenna- 

 way and by Hasselbalch and Lindharel(a) (6) that excretion of acid and of 

 ammonia diminish for a period of several days. During this time the 

 alkalosis will have been diminished and the normal H-ion concentration 

 of the blood almost restored to its previous level. This, as Haggard and 



