Respiratory Function and Age 63 



or 30 breaths, equilibrium is esta])lislu'(l ])ctweon luno and 

 spirometer, with a hehum percentage of 1) 12. 11" the luii^ 

 had been perfectly eftieient from tlie point <»!' view of a 

 ventilation enoineer — i.e., if all the alveoli had been equally 

 ventilated — it can be calculated that equilibrium should have 

 been reached in 23 or 24 breaths, whereas in fact 30 breaths 

 were required, and it is true that most normal individuals 



YOUNG 

 NORMAL 



204060 ?o i5o% 



Fig. G. The efliciency of gas niixino in the hino, expressed as a 

 percentage of perfect elliciency, is shown on the abscissa. 



operate at 70 or 80 per cent efficiency as far as ventilation is 

 concerned. 



The record of a patient with emphysema is also shown in 

 Fig. 5 and here the story is a very different one. Mixing was 

 only complete after ten minutes or 150 breaths. 



In Fig. 6 is shown a summary of our results. Young normals 

 operate at an average of 75 per cent efficiency while the figure 

 for the older group is only 54 per cent, a difference which is 

 statistically significant. This can only mean that with ad- 

 vancing years ventilation of the lungs becomes more uneven, 

 and this is presumably a sequel of loss of elasticity. 



