62 



D. V. Bates and R. V. Christie 



get just its fair share of eacli breath that is taken. Seeondly, 

 the air in eaeh alveolus should I)e fully exposed to the lung 

 capillaries; in other words, the alveolar air should eonie into 

 proper contact with the pulmonary blood. Both of these 

 functions can be measured, and I will first say a word about 

 the efficiency of ventilation which, surprisingly enough, can 

 be measured quite easily and accurately. 



HEALTH 



EMPHYSEMA 



12 3 



MINUTES 



MINUTES 



Fig. 5. Tlie efficiency of gas mixing in the lung measured by the 

 hehum dilution method. In a healthy young individual (on left) 

 equilibrium between spirometer and the lungs is reached after 

 80 breaths; in a patient with emphysema (on right) efjjuilibrium is 

 only reached after 150 breaths. 



If an inert and relatively insoluble gas such as helium is 

 breathed it will mix with the other gases in the alveoli but 

 practically none will be absorbed (Bates and Christie, 1950). 



In Fig. 5 is shown the record of a young normal individual 

 who starts to breathe from a spirometer containing 13-5 per 

 cent helium. The helium percentage, which is measured 

 electrically by a katherometer, falls, and after two minutes, 



