60 



D. V. Bates and R. V. Christie 



aged it averages 3-5 litres and in emphysema the average 

 rises to 4-7 htres. One reason for this increase, and possibly 

 the sole reason, is that the elastic recoil of the lung diminishes 

 with age. During life the lungs remain distended because the 

 elastic recoil is counterbalanced by traction of the chest wall 

 and diaphragm, and expansion of the lung can be brought 



i i 3 



Fig. 3. The distribution of the Functional Residual Capacity (i.e. 



the volume of air in the lungs at the end of an ordinary quiet 



expiration). 



about either by increased traction, such as occurs on inspira- 

 tion, or by diminution in elastic recoil. That the elasticity 

 of the lung does in fact diminish with age can be shown by 

 direct measurement, and I will just say a word about the 

 technique we have used. On inspiration the intrapleural or 

 intrathoracic pressure becomes more negative, and this fall 

 in pressure is a direct measure of the force exerted on the 

 lungs by the muscles of inspiration. The tidal air is a measure 

 of the volume change which occurs. If these two, the intra- 

 pleural pressure and the tidal air, are measured simultan- 

 eously it is quite easy to calculate the amount of work the 



