154 



NA TURE 



[July 29, 1922 



.and maintaining the oxygen pressure in the blood 

 at its sea-level value is unfounded. 



However, the blood as it leaves the lung must 

 contain appreciably less oxygen than its haemoglobin 

 would normally absorb. It is, to use the American 

 phrase ; unsaturated to a considerable degree. Such 

 blood, of course, would lack the bright scarlet colour 

 of true arterial blood. The actual colour of the blood 

 as withdrawn from the radial artery entirely bore out 

 this view ; as it flowed into the syringe it was of a 

 dull red colour often verging on chocolate, and in the 

 case of the natives was 82-86 per cent, saturated with 

 oxygen, instead of 95-96 per cent, as at the sea level. 



Curves giving the relation between the percentage 



saturation of the blood and the partial pressure of 



oxygen in lungs at Lima and Cerro de Pasca for different 



members of the party are shown in Fig. 1, from which 



100 



80 



Meo 



40 



20 



100 



10 20 40 60 80 



— > Partial Pressure ofOxt/get? ttt the Imp 'a/veo// 



Fig. i. 



it is apparent that at high altitudes the partial press- 

 ure required to secure a percentage saturation suffi- 

 cient for life decreases considerably. 



The establishment of the fact that life can be sup- 

 ported with some degree of efficiency with the blood 

 in this condition is of great importance, because in 

 recent years there has been a tendency to assume that 

 a small degree of unsaturation of the arterial blood 

 must of necessity produce very grave results. Fig. 1 

 shows that there is some adjustment of the blood to 

 the new conditions. At Cerro the unsaturation of 

 the blood was written on the faces of the inhabitants. 

 Any one who had any colour in his face was appreci- 

 ably cyanosed. 



2. Increased pulmonary ventilation has been shown 

 by all recent observers to be of great importance as 

 a factor in adaptation to high altitudes. In our case, 

 had our respiration been the same in rate and depth 

 at Cerro as it was at Lima we would have had about 

 40 pressure mm. of carbonic acid and 35 mm. pressure 

 of oxygen in the air of our lungs. In fact, owing to 

 increased respiratory effort, we reduced the carbonic 

 acid to about 25 mm. and raised the oxygen to about 

 52 mm. The importance of these facts is enhanced 

 by the certainty that it is the partial pressure of 



NO. 2752, VOL. I IO] 



oxygen in the alveolar air which regulates the degree 

 of saturation of the blood. 



While the increased ventilation of the lung had been 

 demonstrated by previous observers, the mechanism 

 which was responsible for it had been much in dispute. 

 This we investigated. The mechanism of hyperncea 

 at rest seems to be that first suggested by ilaldane, 

 namely, that the want of oxygen heightens the activity 

 respiratory of the respiratory centre, resulting in a 

 mild degree of forced respiration — so mild as not to 

 be apparent to the subject, yet sufficient to reduce 

 the carbon dioxide content of his blood. Incidentally 

 this process acting alone would make the blood more 

 alkaline. The measurements of hydrogen ion con- 

 centration in the blood of persons at rest bore out 

 this view ; either the blood was more alkaline than 

 at sea level, or it was of approximately the same 

 reaction. 



The effect of exercise on the blood has 

 been more fully investigated, though for the 

 most part by indirect methods. Our results 

 support those already obtained, namely, that 

 a given increment in the hydrogen ion con- 

 centration of the blood is produced by less 

 exercise at high altitudes than at the sea 

 level. Thus the dyspnoea of exercise is the 

 cumulative effect of two factors — an in- 

 creased response of the respiratory centre 

 to a given stimulus, and an increase in the 

 stimulus evoking the response. 



3. I have already alluded to the size of 

 the Cholos chest. With it appears to be 

 associated an interesting modification of its 

 configuration. Fig. 2 shows two X-ray photos 

 of the left sides of two chests photographed 

 from behind. Both pictures were made at 

 mmofflQ Cerro de Pasco. That on the right is my own, 

 and is fairly typical of our party ; that on 

 the left is a typical Cholo chest. There 

 is a marked difference in the angle at which 

 the ribs are carried ; my own slope down from the 

 vertebral column at a quite considerable angle, 

 while those of the native are much more horizontal. 

 It seems highly probable that this horizontal carriage 

 of the ribs indicates a compensatory effort designed 

 to increase the facility with which the blood obtains 

 oxygen, for it is acquired at sea level by persons 

 suffering from emphysema and other complaints in 

 which there is shortness of breath. Several of the 

 mining engineers, of whose chests we took radiograms, 

 showed a similar tendency. At this point another 

 peculiar physical conformation may be mentioned, 

 namely, clubbing of the fingers, which, when found 

 at sea level, is frequently associated with some trouble 

 which prevents sufficient oxygen from reaching the 

 extremities. Though they are not the rule, clubbed 

 fingers are by no means unusual at Cerro de Pasco 

 in persons without any circulatory or respiratory lesion. 

 4. An increase in the number of red blood corpuscles 

 in each cubic mm. of blood has long been known to 

 occur at high altitudes. Systematic researches carried 

 out principally under the direction of Dr. Ilaldane 

 have shown that the increase in the number of red 

 blood corpuscles is associated with an increase in the 

 quantity of haemoglobin present. These two observa- 



