RESPIRATION 



55 



asphyxial symptoms begin to develop. Figure 16 is a tracing 

 which shows this change. Figure 1 7 shows a similar change pro- 

 duced, not by resistance alone, but by the combined effects of 

 resistance and the increased breathing due to muscular work. 



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Ron 



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Figure 16. 

 Effects of heavy resistance. To read from left to right. 



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Figure 17. 

 Effects of resistance and gentle work. To read from left to right. 



It will be shown later that even a slight deficiency in the oxy- 

 genation of the arterial blood favors greatly the development of 

 fatigue symptoms in the respiratory center. But addition of oxy- 

 gen to the air does not prevent the development of fatigue due 

 simply to great extra work thrown on the respiratory center. When 

 the breathing is quite free, and the oxygenation of the blood 

 normal, fatigue does not at all readily show itself, and greatly 

 increased breathing goes on in a normal manner over long periods. 

 During muscular exertion, however, as will be shown later, the 

 oxygenation of the blood may become impaired, in which case 

 fatigue of the breathing may easily show itself, so that the subject 

 becomes in a literal sense "short of breath," since each breath 

 is short. 



