THE VENOUS PULSE 311 



atrio-ventricular base is definitely diminished. It follows 

 that during ventricular contraction the apex may be regarded 

 as a fixed point, although it moves upwards somewhat and 

 presses against the anterior wall of the chest. On the other 

 hand, the atrio-ventricular base, which constitutes the insertion 

 of both the atrial and the ventricular fibres, moves with each 

 atrial and with each ventricular contraction. As the orifices 

 of the great veins are to be regarded as fixed points, the 

 capacity of the atria becomes diminished with each atrial 

 contraction. Ventricular systole pulls the atrio-ventricular 

 base towards the apex and so increases the atrial capacity. 



FIG. in. Tracing of the Normal Venous Pulse, together with 



a Synchronous Tracing of the Radial Pulse. 



The waves, v, a, and c, are referred to in the text. 



During diastole the atrio-ventricular base assumes a position 

 of rest, mid-way between the positions which it occupies 

 during atrial and ventricular contractions, respectively. 



This theory of the action of the cardiac musculature can be 

 applied to the interpretation of the venous pulse. Atrial 

 contraction causes a rise in the intra-atrial blood-pressure 

 and prevents, for the time being, any further outflow from the 

 veins. This condition is indicated by the upstroke of the 

 venous pulse tracing (Fig. in, a). The ensuing ventricular 

 systole is marked on the tracing by the wave c. This does 

 not indicate a true rise in the intra-venous blood-pressure but 

 is transmitted from the common carotid artery. It is su.c- 



