CIRCULATION 



271 



diastole the outflow is again free, a rush of blood takes place 

 into the distending auricles, and thus the pressure in the 

 veins falls. But as this is occurring, blood is shot from the 

 ventricles into the arteries, and the carotid, lying behind 

 the jugular vein, transmits its pulse to the vein as a crest. 

 While the ventricle is contracted blood cannot pass on from 

 the auricles, and hence it accumulates in the great vein and 

 makes a third crest at the end of the ventricular systole. At the 

 moment when the ventricles dilate a sudden rush of blood 

 takes place from the veins and auricles into the ventricles, 

 and thus a sudden fall in the pressure is produced. Gradually, 



FIG. 125. Tracings of the Pulse in the great Veins in relationship to the 



Cardiac Cycle. normal venous pulse. a and b venous pulse 



in tricuspid incompetence. 



as the ventricles fill, the pressure in the auricles and veins 

 increases and they are again expanded. 



This is the normal venous pulse. But, if the auriculo- ven- 

 tricular valves are incompetent, blood is forced back into the 

 auricles and veins when the ventricles contract, and a crest 

 develops after the carotid crest which it may replace. The 

 height of this crest is a good index of the amount of regurgita- 

 tion. 



Respiratory Variations in Blood Pressure 



Not only do rhythmic changes in the arterial pressure occur 

 with each beat of the heart, but larger changes are caused 



