Changes in Breathing and Blood at High Altitudes. 257 



alveolar COa pressure observed for normal women. Whether the fact of my 

 C0 3 pressure remaining at the normal value in spite of the barometric pressure 

 varying from 759 to 663 mm. of mercury is an idiosyncrasy, or an indication 

 that with persons in whom the alveolar CO2 pressure is naturally low a 

 marked decrease of barometric pressure (i.e. more than 100 mm. of mercury) 

 is required to produce a lowering of the threshold value of the C0 2 pressure, 

 can only be determined by further experiments. 



In contrast to the absence of change in the alveolar C0 2 , the haemoglobin 

 in M. P. F. G. rose, as before,* with decreased barometric pressure and fell as 

 sea-level pressure was approached. From an initial value of 89 per cent, at 

 New York, the haemoglobin had after three days at Highlands (altitude 3850 

 feet ; barometric pressure 668 mm. of mercury) risen to 96 per cent. It 

 oscillated during the following four weeks between 91 and 93 per cent, and 

 was 98 per cent, during the eighth week, after a fortnight had been spent at 

 an altitude of 4200 feet. At Waynesville (altitude 2645 feet) it fell to 93 

 per cent., and was again 96 per cent, at Asheville (altitude 2210 feet and 

 barometric pressure 708 mm. of mercury). Three days after the return to 

 New York a lower value than usual was recorded, 87 per cent. The haemo- 

 globin reached 92 per cent, a few days later, and then fell to the normal value 

 of 89 per cent. 



Conclusions. 



1. In persons acclimatised at altitudes up to 3850 feet, the partial pressure 

 of CO2 in the air of the lung alveoli is invariably lower than at sea-level, so 

 that the lung ventilation is correspondingly increased. The results of the 

 present investigation are in accord with those obtained with persons acclima- 

 tised at altitudes of 5000 to 14,000 feet, and support the conclusion previously 

 published that " the lowering of the CO2 pressure is in direct proportion to the 

 diminution of the barometric pressure, and amounts to about 4 - 2 mm. or 10"5 

 per cent, of the sea-level value for each 100 mm. of diminution of barometric 

 pressure." 



2. It is again found that in women, as at sea-level, the alveolar C0 2 pressure 

 is about 3 mm. lower than in men. 



3. As at higher altitudes, in persons acclimatised at altitudes up to 3850 

 feet, the percentage of haemoglobin in the blood is increased. The present 

 observations support the view previously published that "for every 100 mm. 

 fall of atmospheric pressure the percentage of haemoglobin in the blood is 

 increased by about 10 per cent, of the normal value for men at sea-level." 



* Ibid., p. 369. 



