136 



RESPIRATION 



to find that in the deepest alveolar air the oxygen percentage, so 

 far from being lower, was actually higher than usual. There was 

 thus hyperpnoea from want of oxygen, and yet the deep alveolar 

 air contained more oxygen than usual. The breathing was, how- 

 ever, very inefficient and therefore greatly increased in amount, 

 as the dead space told much more than with normal breathing, 

 so that the percentage of CO2 in the expired air was very low. 



On turning the matter over, we bethought ourselves of some 



anatomical observations collected by Professor Arthur Keith in 



''Further Advances in Physiology," edited by Professor Leonard 



Hill, 1909. He showed in this essay that during inspiration the 



.; lungs do not expand equally and simultaneously at all parts, 



but open out part by part, somewhat like the opening of a lady's 



;; fan. The parts nearest the moving chest walls (for instance the 



Ij diaphragm) expand first, and other parts follow. It follows from 



■ ^ this, that in shallow breathing the lungs will be very unevenly 



ventilated. Only certain parts will expand properly, and on ac- 



c5^ 



i 



I 





90 

 80 

 70 

 60 

 50 

 40 

 30 

 20 

 10 



2 4 6 S 10 12 /4 16 Id 2fr22 2426 28 30 32 34 36 38 40 42 44 

 PERCENT OF AN ATMOSPHERE 

 OXYGEN PRESSURE 



Figure 45. 

 Dissociation curves of blood for COj and oxygen. 



count of the increased frequency of breathing they will receive 

 much more than their proper share of fresh air, while the other 

 parts which do not expand will receive much less. 



The consequence of this will be that the venous blood passing 

 through the unexpanded parts of the lungs will be very im- 

 perfectly arterialized, whereas in the expanded parts the blood 

 will be more arterialized than usual. The mixed arterial blood will 

 thus be a mixture of over-arterialized and under-arterialized 



r' 



