264 



VELOCITY OF PULSE WAVE. 



[BOOK i. 



sec. to pass by the lever. Taking the velocity of the pulse-wave 

 as 6 meters per sec. the length of the wave will be T ^ths of 6 m., 

 that is nearly 5 meters. And even if we took a smaller estimate, 

 by supposing that the real expansion and return of the artery at 

 any point took much less time, say j^ths sec -> ^ ne l en gth of the 

 pulse-wave would still be more than 2 meters. But even in the 

 tallest man the capillaries farthest from the heart, those in the tips 

 of the toes, are not 2 m. distant from the heart. In other words, 

 the length of the pulse-wave is much greater than the whole 

 length of the arterial system, so that the beginning of each wave 

 has become lost in the small arteries and capillaries some time 

 before the end of it has finally passed away from the beginning of 

 the aorta. 



We must now return to the consideration of certain special 

 features in the pulse, which from the indications they give or 

 suggest of the condition of the vascular system are often of great 

 interest. 



145. Dicrotism. In nearly all pulse tracings, the curve of the 

 expansion and recoil of the artery is broken by two, three, or several 

 smaller elevations and depressions : secondary waves are imposed 

 upon the fundamental or primary wave. In the sphygmographic 

 tracing from the carotid Fig. 49 and in many of the other tracings 



FiG. 49. PULSE-TBACING FKOM CAKOTID ARTERY OF HEALTHY MAN (from Moens). 



x, commencement of expansion of the artery. A, summit of the first rise. 



C, dicrotic secondary wave. B, predicrotic secondary wave; p, notch preceding this. 



D, succeeding secondary wave. The curve above is that of a tuning-fork with ten 

 double vibrations in a second. 



given, these secondary elevations are marked as B, C, D. When 

 one such secondary elevation only is conspicuous, so that the pulse- 

 curve presents two notable crests only, the primary crest and a 

 secondary one, the pulse is said to be " dicrotic " ; when two 

 secondary crests are prominent, the pulse is often called "tri- 

 crotic " ; where several " polycrotic." As a general rule, the 

 secondary elevations appear only on the descending limb of the 

 primary wave as in most of the curves given, and the curve is 

 then spoken of as " katacrotic." Sometimes, however, the first 

 elevation or crest is not the highest but appears on the ascending 



