228 EFFECT OF PULMONARY VENTILATION 



The efficiency of breathing depends not only on the vital 

 capacity, but on the power of the respiratory muscles and the 

 nervous power of the respiratory centre to maintain an ampler 

 rate and depth of breathing, and on the power of the heart to 

 circulate the blood rapidly. 50 per cent, of the 2 in the 

 arterial blood is normally used up by the tissues ; in hard work 

 the circulation may be so increased in velocity that the loss of 

 2 by the arterial blood is no greater or even less. 



Lewinstein and v. Schrotter found that shallow-breathing 

 animals rabbits, guinea-pigs cannot live for more than three 

 days at 350 mm. Hg = 6000 m. After death their renal 

 tubules, liver cells, muscle-fibres of diaphragm, heart, and arteries 

 show fatty degeneration. 



Living in the Monte Rosa hut (4300 m.) for three weeks, Durig 

 and Zuntz found that their increased breathing almost compensated 

 for the diminished barometric pressure. The compensation was 

 not complete on the first day thus Zuntz increased his alveolar 

 oxygen tension from 53*5-56 mm. Hg on the first day to 

 57-59-7 at the end of their visit, and Durig increased his from 

 48-3-53' 5 to 53-6-55-5. At the same time the air-hunger, felt on 

 effort, passed away. 



By an 2 tension of 48'3 mm. Hg the saturation of Durig's blood 

 would have been only 65-9 1 he suffered at this time from severe 

 migraine, palpitation of the heart, and giddiness. Loewy found 

 that he could endure a greater depression in the pneumatic 

 chamber if he did moderate work, for the exercise increased his 

 depth of breathing and raised the alveolar oxygen tension. 



The mountain-climber needs a powerful heart to rapidly 

 circulate blood through his lungs, and must be a deep breather. 

 Differences in these respects explain the differences of altitude 

 at which men are affected. Loewy finds that the dissociation 

 tension of OHb varies in different men. This is another factor 

 of importance. By respiring oxygen the balloonist and moun- 

 tain climber may withstand the influence of great altitudes. A 

 suitable portable apparatus has been contrived. It consists of a 

 small oxygen cylinder, mask, breathing bag containing soda lime, 

 &c., all supported by straps passing over the shoulders. 



1 Mosso found that the gases of the blood, determined by the Haldane- 

 Barcroft method, are only slightly lessened. Further work is required on this 

 point. 



