1907.] Influence of Increased Barometric Pressure on Man. 287 



The breathing of pure oxygen has been suggested by v. Schrotter (5) as a 

 means of washing the dissolved nitrogen out of the body before decompression. 

 He suggested that deep-sea divers might take down a small cylinder, wash 

 themselves out for five minutes, and then ascend rapidly without risk. 



The experiments of Durig (6) show that, on breathing almost pure oxygen, 

 the body nitrogen is washed out in about five minutes, as shown by the 

 quantity of nitrogen in the expired air sinking in that time to a constant level. 

 L. Hill and C. Ham (7) have pointed out the extreme danger of breathing 

 oxygen for even five minutes at high pressures, and v. Schrotter (8) himself 

 has come to the conclusion that the use of oxygen should be confined to 

 an inhalation immediately after decompression. 



The gas set free in the blood on rapid decompression contains 79 — 87 per 

 cent. N" 2 . Of the alveolar air, nitrogen forms 79 per cent., so that the 

 difference of tension promoting an escape of bubbles is very small or nil 

 (5 — per cent.). 



* If pure oxygen be breathed, the difference of tension will become 79 — 87 

 per cent., and this will greatly favour the escape of nitrogen bubbles from 

 the pulmonary vessels (Zuntz). There is little advantage in breathing 

 oxygen during the course of a rapid decompression, because the exchange is 

 between the tissues saturated with nitrogen and the blood. The amount 

 carried away by the blood depends on the respective tensions of nitrogen in 

 the tissues and the blood. 



Oxygen inhalation cannot affect this, except in so far as it clears the 

 arterial blood of nitrogen in the lungs. If the pressure falls rapidly the 

 tissues will still be saturated — say, at 5 atmospheres — and hold 5 per cent, 

 of nitrogen, while the blood can only carry, say, 3 per cent., the pressure 

 having fallen to 3 atmospheres. Oxygen can have little or no effect in 

 arresting this decreasing power of the blood to carry nitrogen (v. Schrotter). 



The only safe method is slow decompression at a uniform rate when the 

 body has been exposed long enough to become saturated. 



EEFEEENCES. 



(1) Bert, ' La Pression Barometrique,' p. 955. 



(2) Heller, Mager, and Schrotter, ' Luftdruckerkrankungen,' etc., p. 800. 



(3) Hill and Ham, " Phys. Soc. Proc," ' Journ. Physiol./ vol. 33. 



(4) Hill and Macleod, ' Journ. Hygiene,' vol. 3, pp. 401, etc. 



(5) v. Schrotter, 'Der Sauerstoff in der Prophylaxe, etc., der Luftdruckerkrankungen, 



etc., 1 p. 71 etc. 



(6) v. Schrotter, op. cit., p. 49. 



(7) Hill and Ham, " Phys. Soc. Proc," ' Journ. Physiol.,' vol. 33. 



(8) v. Schrotter, 'Zur Prophylaxe der sogennanten Taucherlahmung ' (Congresso 



Internazionale per le Malattie del Lavoro). 



