THE REGULATION OF BREATHING 



290 



Hyperpncea, Dyspnoea. - - By 

 hyperpncea, increased volume of 

 breathing is designated; dyspnoea, 

 on the other hand, applies to dis- 

 tressful breathing. Both may be 

 induced by the agencies which 

 excite the respiratory centre to 

 increased action, such as excess of 

 carbon dioxide, want of oxygen, 

 diminished alkalinity of the blood, 

 due to acid formation, and rise in 

 the temperature of the 'blood (heat 

 dyspnoea). The cardiac dyspnoea 

 of heart disease is chiefly due to 

 want of oxygen. 



Apnoea. The condition of "no 

 breathing " is due to a lack of 

 chemical stimulation of the respi- 

 ratory centres. It occurs after 

 forced breathing which washes 

 out carbon dioxide from the blood 

 (Fig. 164). It is claimed that 

 there exists also a " vagus " apnoea, 

 produced in animals by repeated 

 rapid distension of the lungs by 

 artificial means. By this means 

 the inspiration-inhibiting fibres of 

 the vagus are so stimulated that 

 apnoea ensues. This apnoea may 

 be due to washing carbon dioxide 

 out of the blood, but it is more 

 difficult to obtain when the vagi 

 are cut; it is stated that if the 

 ventilation of the lungs be made 

 with an indifferent gas, such as 

 hydrogen, it is possible to obtain 

 apnoea, but not after the vagi are 

 cut (Figs 165, 166). It is very 

 doubtful if vagus apnoea occurs 

 in man, for it has been shown that 

 apnoea cannot be produced if the 

 alveolar air percentage of CO 2 is 

 not reduced below the normal CO 2 

 percentage. 



Periodic, Grouped, or Cheyne- 

 Stokes Breathing. Group breath- 

 ing is natural in young children 

 when asleep, and in hibernating 



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