Respiratory Function and Age 



61 



respiratory muscles liave to do in order to distend the lungs. 

 It is also possible to indicate how much of this work is ex- 

 pended on the elastic resistance of the lungs and how much 

 on the viscous or non -elastic resistance (Mcllroy, Marshall 

 and Christie, 1954). 



In Fig. 4 is shown a summary of our results. In eight 

 healthy individuals below the age of thirty-five, between 70 



Fio. 4. The proportion of respiratory work expended against the 

 elastic resistance of the lung. 



and 80 per cent of the work of breathing was expended 

 against elastic resistance. In seven healthy individuals over 

 the age of fifty, only between 50 and 60 per cent was expended 

 against elastic resistance, and in emphysema the percentage 

 is even lower. It is fair to conclude that with advancing 

 years the elastic resistance or elastic recoil of the lungs is 

 reduced (Mcllroy and Christie, 1954). 



So much for the mechanical aspects of lung function. 



The sole function of the lung is to ventilate the blood, 

 and if it is to do this with maximal efficiency it must have at 

 least two characteristics. Firstly, the lung should be venti- 

 lated evenly throughout; in other words each alveolus should 



