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 CO 2 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 

 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- 



6.6 6.0 



PRESSURE OF CO^ 

 PERCENT OF AN ATMOSPHERE 

 S3 4.6 4.0 3.3 2.6 



20 /.3 0.7 



024 



68/0/2 14 16 Id 20~Z2 24 26 26 30 32 54 36 38 4042 44 3 

 PERCENT OF AN ATMOSPHERE ^ 



OXYGEN PRESSURE 



Figure 45. 

 Dissociation curves of blood for COa 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 



