PULSE TRACINGS. 311 



shock is given to the column of blood, and the fluid next the 

 valves is moved forward with great velocity. Owing to its in- 

 ertia the fluid tends to pass onward from the valves, and thus 

 allows a momentary fall in pressure, which is at once followed by 

 the reflux of the blood and the forcible closure of the valves. 



The first crest or apex of the pulse curve corresponds to the 

 shock given by the systole, and is greatly exaggerated by the 

 inertia of the lever. The crest of the predicrotic wave marks 

 the moment when the blood ceases to flow from the ventricle, and 

 therefore it is the real head of the pulse wave. 



The dicrotic wave has been explained as (1) a wave of oscil- 

 lation, or (2) a wave reflected from the periphery. If the former, 

 it should be less marked than the predicrotic, which by this theory 



FIG. 140. 



Trauing drawn by Marey's Sphygmograph. The surface moved from right to left. 

 The vertical upstrokes show the period when the shock is given by the systole of the 

 ventricle. The upper wave on thedownstroke shows when the blood has ceased to enter 

 the aorta. Then comes the dicrotic depression, which is a negative wave produced by the 

 momentary backflow in aorta, and the dicrotic elevation caused by the closure of the 

 valves. 



is said to be the first wave of oscillation, for each succeeding 

 oscillation is less than its forerunner. But, as already men- 

 tioned, the dicrotic is invariably the larger. 



There are many reasons why it cannot be a wave of reflection 

 from the periphery of the arterial tree; viz., 1. Its curve is not 

 nearer the primary wave when the peripheral vessels are ap- 

 proached. 2. The arterioles which form the peripheral resistance 

 are at too irregular distances to give one definite wave of reflec- 

 tion. 3. It is seen in the spurting of an artery cut off* from the 

 periphery. 4. It increases with the greater elasticity and low ten- 

 sion, while the reflected waves diminish. 



The dicrotic notch depends upon a negative wave caused by 

 the sudden stop of inflow and the momentary reflux of blood 



