RESPIRATION 



117 



CO2 pressure is only reduced to about half. During heavy muscu- 

 lar exertion, on the other hand, the breathing may easily be in- 

 creased to ten or fifteen times its normal amount. The relatively 

 slight increase in the amount of air breathed during very serious 

 anoxaemia is frequently lost sight of in the interpretation of 

 clinical symptoms. There is nearly always a considerable increase 

 in the frequency of breathing, but the depth of breathing is 

 usually only slightly increased, and may be diminished, as will 

 be explained more fully below. In the very dangerous pure anox- 

 aemia of high altitudes or CO poisoning, increase in the breathing 

 is not a prominent symptom. 



' Tl has been known for long that at high altitudes the breathing 

 is very apt to be periodic. This phenomenon was fully observed 

 on Monte Rosa by Mosso,^ who, however, had completely failed 

 to realize the significance of Paul Bert's researches on the effects 

 of gases, and thus failed to interpret correctly the cause of the 

 periodic breathing. The periodic breathing is usually not con- 

 tinuous, but can easily be started by disturbing the ordinary 

 rhythm of breathing, as by taking a few long breaths, or holding 

 the breath. It is also very apt to occur at night. It is distinguished 

 from ordinary clinical Cheyne- Stokes breathing by the shortness 



rtRVALS OF 5 SECONDS 



Figure 38. 

 Henderson, August 13. Quantitative record of the respiration during periodic 

 breathing. Inspiration upwards. 



of the periods. There are usually groups of only about three to 

 six breaths, followed by a pause, and this periodic sequence con- 

 tinues almost indefinitely (Figure 37). Sometimes the middle 

 breath of the group is deepest, sometimes the last breath (Figure 

 38) or sometimes the breaths are about equal in depth. Some- 

 times the periodicity only shows itself by periodically recurring 

 single deep breaths. 



The general explanation of this periodic breathing has already 

 been given in Chapter V. That this explanation is the correct one 

 is shown by the fact that, as is seen in Figure 37, on adding oxy- 



* Mosso, Life of Man on the High Alps, Chapter III, London, 1898. 



