REGULATION OF RESPIRATORY MOVEMENTS 



1097 



which is spoken of as Cheyne-Stokes respiration. During the period of 

 apnoea, resulting on forced breathing, the great diminution of oxygen 

 tension in the alveoli is shown by the fact that the subject of the experi- 

 ment becomes blue, and may indeed lose consciousness. There are at the 

 same time rhythmic changes in the blood-pressure, which rises towards the 



FIG. 515. Forced breathing of air for two minutes, followed by apncea for two 



minutes, and periodic (' Cheyne-Stokes ') breathing for about five minutes. 

 At A, sample of alveolar air contained 2 , 11-44 per cent. ; C0 2 , 5-58 per cent. 

 Second sample at B, O 2 , 13-55 per cent. : CO 2 , 5-57 per cent. (DOUGLAS and 

 HALDANE.) 



ends of the periods of the apnoea, falling during the periods of respiration. 

 The first respiration after forced breathing is due to. oxygen lack. The 

 period of apncea may therefore be considerably prolonged, if the onset of 

 oxygen lack be postponed, by increasing the tension of this gas in the alveoli v 

 at the commencement of the apnceic period. By forcibly breathing for a 

 period of two minutes in an atmosphere of oxygen, men have succeeded in 

 holding their breath for as long a period as eight minutes (Vernon). 



'Cheyne-Stokes ' breathing is almost invariably observed as one of the effects of 

 exposure to high altitudes, and is then especially marked during sleep. It is often present 

 when the activity of the respiratory centre is depressed, as in cases of uraemia or per- 

 nicious anaemia. Under these circumstances it may be temporarily removed by^ 

 administering either oxygen or carbon dioxide (in small percentage) to the patient. 

 The oxygen improves the condition of the centre ; the carbon dioxide acts as an added 

 stimulus and rouses its activity. 





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