THE CIRCULATION 



255 



of blood from the arteries, and if at the same time the out- 

 flow from the capillaries is not proportionately increased, 

 intermittent inflow and resistance to outflow are developed, 

 and a pulse is produced. Such a condition is seen in certain 

 glands during activity. 



C. Yenous Pulse. 



1. The absence of a general venous pulse has been already 

 explained. But just as in the capillaries so in the veins, a 

 local pulse may develop. 



2. In the veins entering the auricles a pulse occurs, 

 but a pulse having no resemblance to the arterial pulse, 

 although depend- 

 ing on the same 



three factors. 



Its form is indi- 

 cated in Fig. 122. 



Its features are 

 to be explained as 

 follows : 



Blood is con- 

 stantly flowing 

 into the great 

 veins, pressed on 

 by the vis a tergo. 

 When the auricles 

 contract the out- 

 flow from these 

 veins into the heart is suddenly checked, and consequently 

 the veins distend. At the moment of auricular 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 the ventricular systole prevents 

 blood from passing through the auricles, a second obstruction 

 to outflow occurs, and thus a second increase in pressure is 

 developed in the veins. 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, as the ventricles fill, the 



FIG. 122. Tracings of the Pulse in the great Veins 

 in relationship to the Cardiac Cycle. 



Normal Venous Pulse. 



Venous Pulse in Tricuspid Incompetence. 



