REGULATION OF RESPIRATORY MOVEMENTS 1223 



Apnoea spuria. Stoppage of respiration by stimulation of other nervous or 

 sensory surfaces. Thus when a duck plunges there is immediate stoppage of 

 respiration, which may last four or five minutes if the animal remains so long 

 under water. The same stoppage may be produced by pouring water on the 

 beak. 



' CHEYNE-STOKES ' BREATHING 



If a man desires to hold his breath for some time he takes 

 first a series of deep breaths. The result is to diminish the carbon 

 dioxide tension in the alveoli and therefore to take away the need 

 and the desire to breathe until the carbon dioxide tension rises 

 to normal as the result of the continued formation of carbon 

 dioxide. By continuing forced respiratory movements for a 

 minute or two the carbon dioxide tension both in the alveoli 



FIG. 513. Forced breathing of air for two minutes, followed by apncea for two 

 pi>| 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, 2 , 13-55 per cent. ; C0 2 , 5-57 per cent. (DOUGLAS 

 and HALDANE.) 



and in the blood may be brought down to a very considerable 

 extent. As a result there is a prolonged period of apncea. During 

 this period of cessation of respirations, however, the oxygen is being 

 used up, and the tension of this gas in the alveoli may fall to such 

 an extent that the respiratory centre is excited by lack of oxygen 

 before the carbon dioxide tension in the alveoli has risen to its normal 

 value. As a result of the excitation by oxygen lack, a few breaths 

 are taken and the carbon dioxide tension is once more lowered, and 

 the stimulation due to the oxygen lack, disappears. There is therefore 

 again a cessation of respiration. These periods of cessation alternate 

 with periods of respiration so that we get a condition of periodic 

 breathing which is spoken of as Cheyne-Stokes respiration. During 

 the period of apncea, resulting on forced breathing, the great: 

 diminution of oxygen tension in the alveoli is shown by the fact that 

 the subject of the experiment becomes blue, and may indeed lose 

 consciousness. There are at the same time rhythmic changes in the 

 blood pressure, which rises towards the ends of the periods of the 

 apncea, falling during the periods of respiration. The first respiration 

 after forced breathing is due to oxygen lack. The period of apncea 



