526 CIRCULATION OF BLOOD AND LYMPH. 



wave is stopped by the sudden stretching of the aortic valves, 

 which, on losing their firm support, have now themselves to bear 

 the resistance of the arterial pressure. This sudden checking of 

 the negative wave starts a second positive wave, which is prop- 

 agated through the arterial system as the dicrotic wave." The 

 smaller waves, such as the predicrotic, have been explained 

 simply as reflected waves, or as instrumental errors, due to fling 

 of the lever. According to some authors,* an important 

 perhaps the chief factor in the production of the secondary 

 waves is the reflection that occurs from the periphery. Where 

 each arterial stem breaks up into its smaller vessels the main 

 pulse wave suffers a reflection, a wave running backward toward 

 the heart. It is probable that such reflected waves from different 

 areas for instance, from the coronary system, the subclavian 

 system, the mesenteric system, etc. meet in the aorta and 

 may in part soimmate to larger waves, which again pass peripher- 

 ally. The catacrotic waves, according to this view, probably 

 differ in character in the different arteries, and tracings indicate 

 that this is the case. The radial pulse differs, for instance, from 

 the carotid pulse in the character of its waves. Between these 



Fig. 215. Anacrotic pulse from a case of aortic stenosis (Mackenzie): b, The anacrotic 



wave. 



opposite views it is not possible to decide, but it is perhaps 

 permissible to believe that while the dicrotic wave is due pri- 

 marily to the impulse following upon the closure of the semilunar 

 valves, nevertheless the actual form of this and the other second- 

 ary waves is variously modified in different parts of the system 

 by the reflected waves from different peripheral regions, f 



Anacrotic Waves. As was said above, the anacrotic limb 

 under normal conditions shows no secondary waves. Under 

 pathological conditions, however, a secondary wave more or less 

 clearly marked may appear, as is shown, for instance, in the 

 tracing given in Fig. 215. Such waves are recorded in cases of 

 stiff arteries or stenosis of the semilunar valves. In the normal 

 individual an anacrotic pulse in the radial may be obtained, 

 according to von Kries,J by raising the arm. He believes that 

 in this position the reflection of the pulse wave from the periph- 



* See von Frey, loc. tit. 



t For a general discussion, see Tigerstedt, "Ergebnisse d. Physiologic," 

 vol. viii., 1909. 



J Von Kries, "Studien zur Pulslehre," 1892. 



