Studies ox Lung Volume 



153 



and of nitrogen loss by blood). If, on the other hand, com- 

 plete mixture is defined as the condition where the initial dif- 

 ference between bag air and lung air has disappeared then it is, 

 as our experiments show, possible to obtain such a mixture. An 

 analysis in Table I and Fig. 2 shows that the point of full mix- 



23456789 

 No. of respirations 



Fig. 2 



Mixing curves obtained by taking repeated samples of air from bag (lower 

 curve) and from alveoli (upper curve). 



ture is reached when the upper curve is at its lowest point. If 

 rebreathing is continued a steady slight increase in the nitrogen 

 percentage of bag and alveolar air is seen. This is due to the 

 interchange between blood gases and alveolar and can not be 

 overcome by prolonging the experiment. On the contrary, if the 

 rebreathing is continued longer than necessary, the inevitable 

 error due to the alveolar interchange increases. The point of 

 full mixture is therefore indicated by the lowest point of the 

 alveolar curve, and the value for the nitrogen percentage which 

 is most correct is the corresponding point of the lower curve. 





















/ 































































1 2 3 4 5 6 7 6 

 No. of nesptraocra 



Percentage of hydrogen from 



lost part of expiration (alveolar air) 



Percentage of hydrogen from 



beginning of expiration 



Fig. 3 



Mixing curves from hydrogen experiment. Samples taken at the first part 



( ) and the last part ( ) of the experiment. Crossing of curves 



indicates mixture. 



