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HANDBOOK OF PHYSIOLOGY. 



ccpted notion among clinical observers, is that the dicrotic wave is due 

 to the rebound from the aortic valves which causes a second wave; but 

 the question cannot be considered settled, and the presence of marked 



dicrotism in cases of hemorrhage, 

 of anaemia, and of other weaken- 

 ing conditions, as well as its pres- 

 ence in cases of diminished pres- 

 sure within the arteries, would 

 imply that it might, at any rate 

 sometimes, be due to the altered 

 specific gravity of the blood within 

 the vessels, either directly or 

 through the indirect effect of these 

 conditions on the tone of the arte- 

 rial walls. 



Waves may be produced in any 

 elastic tube when a fluid is being 

 driven through it with an inter- 

 mittent force, such waves being 

 called waves of oscillation (M. Fos- 

 ter). Their origin has received 

 various explanations. In an arte- 

 rial schema they vary with the spe- 

 cific gravity of the fluid used, and 

 with the kind of tubing, and may 

 be therefore supposed to vary in 

 the body with the condition of the 

 blood and of the arteries. 



Some consider the secondary 

 waves in the downstroke of a nor- 

 mal tracing to be oscillation waves; 

 but, as just mentioned, even if 

 this be the case, as is most likely 

 with post-dicrotic waves, the dicro- 

 tic wave itself is almost certainly due to the rebound from the aortic 

 valves. 



The anacrotic notch is usually associated with disease of the arteries, 

 e. g., in atheroma and aneurism. The dicrotic notch is called diastolic 

 or aortic, and in point of time indicates the closure of the aortic valves. 

 Of the three main parts then of a pulse tracing, viz., the percussion 

 wave, the tidal, and the dicrotic, the percussion wave is produced by 

 sudden and forcible contraction of the heart, perhaps exaggerated by an 

 excited action, and may be transmitted much more rapidly than the 

 tidal wave, and so the two may be distinct ; frequently, however, they 



FIG. 130. Diagrams of pulse curves with 

 exaggeration of one or other of the three waves. 

 A, percussion; B, tidal; c, dicrotic. 1, percus- 

 sion wave very marked; 2, tidal wave sudden; 

 3, dicrotic pulse curve; 4, and 5, the tidal wave 

 very exaggerated, from high tension. (Maho- 

 med.) 



