THE PULSE. 529 



sudden block causes a reflected wave which passes centrifugally 

 over the arterial system. The dicrotic wave is preceded by a 

 small negative wave or notch in the curve which marks the time 

 of closure or just follows the closure of the semilunar valves. The 

 sequence of events as pictured by Mackenzie* is as follows: "As 

 soon as the aortic pressure rises above the ventricular the valves 

 close. At the moment this happens the valves are supported by 

 the hard, contracted ventricular walls. The withdrawal of the 

 support by the sudden relaxation of these walls will tend to produce 

 a negative pressure wave in the arterial system. But this negative 

 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 



Fig. 215. Anacrotic pulse from a case of aortic stenosis (Mackenzie): 6, The anacrotic 



wave. 



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

 of the lever. While the dicrotic wave is due primarily to the im- 

 pulse following upon the closure of the semilunar valves, neverthe- 

 less the actual form of this and the other secondary waves is va- 

 riously modified in different parts of the system owing to imperfect 

 transmission along the extensible arteries and to the effect of 

 reflected waves from different peripheral regions, f Wiggers lays 

 stress upon the marked difference between the central pulse as 

 recorded in the arteries near the heart (subclavian and lower car- 

 otids) and the peripheral pulse as recorded in the radial. This dif- 

 ference is shown in Fig. 215a, in which, as explained in the legend, 

 the subclavian pulse exhibits several significant pressure changes 

 that are lacking in the radial pulse. 



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 



* Mackenzie, "The Study of the Pulse and the Movements of the Heart," 



fFor a general discussion, see Tigerstedt, "Ergebnisse d. Physiologic/' 

 vol. viii., 1909, and Wiggers, "Circulation in Health and Disease," 1915. 

 34 



