254 A MANUAL OF PHYSIOLOGY 



asphyxia begins. When the respiration is stopped in 

 collapse, instead of a fall a steady rise of pressure occurs 

 (as in Fig. 56, p. 163). This ultimately merges in the 

 elevation due to asphyxia, which shows itself sooner than 

 in inflation, since the lungs contain less air. The difference 

 in the course of the blood -pressure curve in the two cases 

 immediately after stoppage of respiration cannot, however, 

 depend on this latter circumstance. It is undoubtedly due 

 to the fact that in artificial inflation the vascular capacity 

 of the lungs is less and the resistance greater than in 

 collapse. When the tracheal cannula is closed in natural 

 respiration, no initial fall of pressure takes place (Fig. 88). 

 To sum up the causes of the respiratory oscillations in the 



FIG. 88. BLOOD-PRESSURE TRACING (RATIBTT, UNDER CHLORAL). 



Natural respiration stopped at I in inspiration, at Ein expiration. The mean blood- 

 pressure is scarcely altered ; but the respiratory waves become much larger owing to 

 the abortive efforts at breathing. Time-tracing shows seconds. 



arterial blood-pressure : The changes of intra-thoracic pressure 

 and of the vascular resistance in the lungs seem the most important 

 factors, but nervous influences may also play a subordinate part. 



The respiratory oscillations in the veins, as might be 

 expected, run precisely in the opposite direction to those in 

 the arteries, and so do the Traube-Hering curves. The 

 increased flow from the veins to the thorax during inspira- 

 tion lowers the pressure in the jugular vein, while it 

 increases the pressure in the carotid. The constriction of 

 the small bloodvessels to which the Traube-Hering curves 

 are due increases the blood-pressure in the arteries, because 

 it increases the peripheral resistance to the blood-flow ; in 

 the veins it lowers the pressure, because less blood gets 

 through to them. Accordingly, when the Traube-Hering 



