RESPIRATION 253 



a more copious stream begins to flow through the lungs, 

 this is succeeded by a rise. 



In like manner the first effect of expiration, which 

 increases the resistance and diminishes the capacity of the 

 pulmonary vessels, is to force out of the lungs into the left 

 auricle the blood for which there is no room. This causes 

 a temporary rise of arterial blood-pressure, succeeded by a 

 fall as soon as the lessened blood-flow through the lungs is 

 established. 



In artificial respiration oscillations of blood -pressure, 

 synchronous with the movements of the lungs, are also 

 seen, even when the thorax is opened. In the latter case 



I FIG. 87. EFFECT ON BLOOD-PRESSURE OF INFLATION OF THE LUNGS 

 (RABBIT). 



Artificial respiration stopped in inflation at i. Interval between 2 and 3 (not repro- 

 duced) 51 seconds, during which the curve was almost a straight line. Time-tracing 

 shows seconds. 



there are, of course, no variations of intra-thoracic pressure, 

 and the oscillations must be connected with the changes in 

 the pulmonary circulation. The respiratory waves differ in 

 certain respects from those in natural breathing, as might 

 be expected from the very different mechanical conditions. 

 During inspiration (inflation) there is first a small rise and 

 then a large fall of pressure. In expiration (collapse) there 

 is first a slight fall and then a great rise. 



The meaning of this is clearly seen when artificial respira- 

 tion is stopped at the height of inflation (Fig. 87). The 

 arterial blood-pressure then falls rapidly, and continues low 

 until the stock of oxygen is exhausted and the rise of 



