CIRCULATION OF THE BLOOD. 



147 



of pressure during the elastic recoil, in consequence of a rebound from 

 the periphery, and it may indeed be produced on a schema by obstructing 

 the tube at a little distance beyond the spot where the sphygmograph 

 is placed. Against this view, however, is the fact that the notch 

 appears at about the same point in the 

 downstroke in tracings from the carotid 

 and from the radial, and not first in 

 the radial tracing, as it should do, since 

 that artery is nearer the periphery than 

 the carotid, and as it does in the cor- 

 responding experiment with the arterial 

 schema when the tube is obstructed. 

 The generally accepted notion among 

 clinical observers, is that the dicrotic 

 wave is due to the rebound from the 

 aortic valves causing a second wave; but 

 the question cannot be considered set- 

 tled, and the presence of marked dicro- 

 tism in cases of haemorrhage, of anaemia, 

 and of other weakening conditions, as 

 well as its presence in cases of dimin- 

 ished pressure within the arteries, would 

 imply that it might, at any rate some- 

 times, 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 arterial walls. Waves may be 

 produced in any elastic tube when a 

 fluid is being driven through it with an 

 intermittent force, such waves being 

 called waves of oscillation (M. Foster). 

 They have received various explana- 

 tions. In an arterial schema they vary 

 with the specific 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 normal 

 wave to be due to oscillation; but, as just mentioned, even if this be the 

 case, as is most likely, with post-dicrotic waves, the dicrotic 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 indicates closure of the aortic valves. 



Fio. 131. Diagrams of pulse curves with 

 exaggeration of one or other of the three 

 waves. A, percussion; B, tidal: C, dicrotic. 

 1, percussion wave very marked; 2, tidal 

 wave sudden; 3, dicrotic pulse curve; 4 and 

 5, the tidal wave very exaggerated, from 

 high tension. (Mahomed.) 



