RESPIRATION 



99 



noea of 2 minutes about 600 cc. of CO2 were regained, and about 

 200 cc. more during two minutes of periodic breathing which 

 followed. The remainder was regained during the following six 

 or eight minutes. In this latter period the alveolar CO2 pressure 



Figure 31. 

 Effect of a breath of air containing 9.0 per cent of CO2 during apnoea follow- 

 ing forced breathing. Crosses show inspiration and expiration of breath. After 

 an interval there are three deep, and two shallow, breaths, followed by a long 

 apnoeic interval, after which the usual periodic breathing begins. To read 

 from left to right. Time-marker := i second. 



was practically normal, but the respiratory quotient very low, in 

 correspondence with the very high respiratory quotient during 

 the forced breathing. 



What approximately happens to the CO2 pressure in the al- 

 veolar air and respiratory center is represented in Figures 32 and 



■50 



-40 



-zo 



20 



8 



Time in Minufes 



Figure 32. 

 Approximate variations in CO2 pressure of arterial and venous blood dur- 

 ing and after forced breathing of oxygen for two minutes, 



33. The pressure of CO2 in the respiratory center is assumed to be 

 about equal to that of the mixed venous blood, though it is prob- 

 ably lower. 



