146 



THE PERCENTAGE OF CARBON DIOXIDE IN 

 EXPIRED ALVEOLAR AIR. 



By Ethel C. Pinkerton, B.Sc. (Syd.), Government Research 

 Scholar in the University of Sydney. 



(From the l'hysioh>yical Laboratory of the University of Sydney.) 



Introduction. — Since it first appeared probable to physiologists 

 tliat the exchange in the lungs between the gases of the air 

 and of the blood were governed by the laws of diffusion, attempts 

 have been made to ascertain the composition of the air in contact 

 with the respiratory epithelium of the pulmonary alveoli. The 

 early attempts made by Pfliiger(l), Wolff berg (2), and Nuss- 

 baum(3) with an inflated balloon surrounding a catheter, by 

 means of which a bronchus could be blocked, and samples taken 

 from the enclosed area, yielded uncertain results under the same 

 conditions. The figures for carbon dioxide were also lower than 

 those obtained by determinations of the tensions of carbonic acid 

 gas in blood and serum. In LS90, Ch. Bohr (4) showed that the 

 tensions of gases in the alveoli could be ascertained from a know- 

 ledge of the volume of the expired air, A, and of the volume of 

 the "dead space", a. If the percentage of carbon dioxide in the 

 inspired air be designated by J, the percentage of the same gas 

 in the expired air as E, and in the alveolar air as X, 

 AE = (A-a)X + aJ 



, .. AE - aJ 



whence X ^ — 



A-a 



As the figure for the percentage of carbon dioxide in inspired 



air is negligible, the equation may be simplified to 



^ AE 



~A-a 



Zuntz, his co-workers and pupils, have made use of this method. 



Owing to the difficulty in measuring the volume of the "dead 



space", this method is of limited application. It was not until 



the publication of a method by Haldane and Priestley in 1905(5), 



