THE EFFECT OF SUSPENDED RESPIRATION ON THE COMPOSITION 

 OF ALVEOLAR AIR. 



By H. S. Halcro Wardlaw, D.Se. 



(From the Physiological Laboratory of the University of Sydney.) 



[Read 29th November, 1922.] 



In a previous communication the present author has described the change 

 which takes place in the composition of alveolar air when the ventilation of the 

 lungs is stopped by holding the breath, or by rebreathing the same air (Wardlaw, 

 1916). 



When the ventilation of the lungs was stopped by holding the breath under 

 normal or atmospheric pressure, the carbon dioxide content of the alveolar air 

 rose as the period of holding the breath increased. The rise showed two distinct 

 phases. 



During the first 30 seconds the alveolar carbon dioxide rose in a manner 

 which could be expressed by an exponential formula. In other words, the rate 

 at which the carbon dioxide content was rising at any instant depended on the 

 difference between the carbon dioxide content at that instant and a certain final 

 or constant value which it seemed to be approaching. This final value was 

 6.7 % or 48.5 mm. Hg. After holding the breath for about 30 seconds the 

 average carbon dioxide content of the alveolar air had reached 6.6% or 48.1 mm. 

 Hg. and had almost ceased to rise. 



As the holding of the breath continued, however, the second phase appeared, 

 and the alveolar carbon dioxide content began sharply to rise again. The ex- 

 periment could be continued only 5-6 seconds after the appearance of this second 

 phase owing to the difficulty of holding the breath longer than about 35 seconds 

 under the conditions of the experiment. 



When the ventilation of the lungs was stopped by holding the breath under 

 a negative pressure of about 30 mm. Hg less than atmospheric pressure, or by 

 rebreathing the same air from a bag, the alveolar carbon dioxide content again 

 rose as the period of holding the breath, or of rebreathing, increased; 

 but the rise in this case showed only one phase. During the whole period of the 

 experiment the alveolar carbon dioxide content rose in a manner which could 

 be expressed by an exponential formula. The final or constant value which 



