THE PULSE. 



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 (Lan- 

 dois)* simply as elasticity waves, that is, as elastic vibrations of 

 the arterial walls or as instrumental errors, due to fling of the lever. 

 According to other authors, f 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 summate to larger waves 

 which again pass peripherally. 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 opposite views it is not possible to decide, but it is 

 perhaps permissible to believe that while the dicrotic wave is due 

 primarily to the impulse following upon the closure of the semilunar 

 valves, nevertheless the actual form of this and the other secondary 



Fig. 203. Anacrotic pulse from a case of aortic stenosis (Mackenzie) : b. The anacrotic- 



wave. 



waves is variously modified in different parts of the system by the 

 reflected waves from different peripheral regions. 



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. 

 203. Such waves are recorded in cases of stiff arteries or stenosis- 

 of the semilunar valves. In the normal individual an anacrotic 

 pulse may be obtained, according to von Kries,t by raising the 

 arm. He believes that in this position the reflection of the pulse 

 wave from the periphery is favored, and that the anacrotic wave is- 

 simply a quickly reflected wave. It is possible that the same 

 explanation will hold for its appearance under pathological con- 

 ditions. 



* Landois, "Die Lehre von Arterienpuls, " 1872. 



t See von Frey, loc. cit. 



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



