566 THE RESPIRATORY EXCHANGE 



during the onset of violent hyperpncea due to air rich in carbon 

 dioxide. 



Abnormal breathing is one of the conditions which most 

 frequently demands the attention of the physician. It may 

 occur in various forms, hyperpncea, dyspnoea, apnoea, or that 

 alternation of hyperpncea and apnoea which is known as Cheyne- 

 Stokes's respiration. The abnormal condition may be shown 

 in alterations in the rhythm, in the rate or depth of breathing, or 

 in any combination of these. Exact observations do not exist 

 for an adequate discussion of these pathological questions, even 

 if it were within the scope of this work and the power of the writer. 

 It may be of interest, however, to consider briefly some of the 

 pathological conditions which throw light upon the normal regula- 

 tion of respiration. 



In addition to the hyperpnoea produced by breathing carbon 

 dioxide and by muscular work, there is another form of hyper- 

 pncea due to want of oxygen ; this occurs at very high altitudes, 

 where the pressure of oxygen is less than 13 per cent, of an 

 atmosphere, 1 in carbon monoxide poisoning, and sometimes in 

 mines. The rapid ventilation of the lungs in these cases lowers 

 the pressure of carbon dioxide in the arterial blood below the 

 value necessary for excitation of the respiratory centre ; the 

 frequency and depth of respiration are regulated by the pressure 

 of oxygen in the blood. In patients in whom the circulation 

 is inadequate, owing to heart-disease or other causes, this form 

 of hyperpnoea is very common. The cyanosis is evidence of 

 the want of oxygen ; the increased ventilation of the lungs is 

 inadequate, owing to the feeble circulation, to supply the necessary 

 oxygen to the medulla oblongata, but can reduce the pressure 

 of carbon dioxide below the stimulating value. 



A very marked disturbance of respiration is seen in cases of 

 diabetic coma ; the deep ventilation of the lungs, the so-called 

 " air-hunger," is very typical ; there is no obstruction to the free 

 entry and exit of the air, but the rapid and deep breathing persists, 

 it may be for hours. Many observers maintain that in these cases 

 the blood is unable, owing to its diminished alkalinity, to take up 

 the normal amount of carbon dioxide, and thus the tissues are 

 overcharged with the gas, and the respiratory centre is stimu- 



1 See chapter on " Mountain Sickness " by L. Hill, page 215. 



