CIRCULATION. 435 



the sphygmograms commonly obtained from the healthy human radial pulse. 

 When this trace was taken, the subject's heart was beating from 58 to 60 times 



FIG. 111. Sphygmogram from a normal human radial pulse beating from 58 to 60 times a minute. To be 

 read from left to right (Burdon-Sanderson). 



a minute. The trace records the effects upon the lever of five successive com- 

 plete pulsations of the artery, which all agree in the general character of their 

 details, while differing in minor respects. By the tracing of each pulsation 

 the up-stroke is shown to be sudden, brief, and steady, while the down-stroke 

 is gradual, protracted, and oscillating. The commencing recoil of the arterial 

 wall succeeds its expansion with some suddenness. In many sphygmograms 

 this is exaggerated by the inertia of the instrument. As shown by the trace rep- 

 resented in the figure, and by most such traces, the recoil soon changes from 

 rapid to gradual, and, in the trace, its protracted line becomes wavy, indicating 

 that the slow diminution of calibre varies its rate, or even is interrupted by one 

 or more slight expansions, before it reaches its lowest, and is succeeded by the 

 up-stroke of the next pulsation. In each of the five successive pulsations the 

 traces of which are shown in Figure 111, the line which represents the more 

 gradual portion of the down-stroke of the pulse is made up of three waves, 

 of which the first is the shortest, the last the longest and lowest, and the mid- 

 dle one intermediate in length, but by far the highest. This middle wave is, 

 in fact, the only one of the three to produce which an actual rise of pressure 

 occurs ; in each of the other two, no rise, but only a diminished rate of decline, 

 is exhibited. The changes of pressure which produce the first and third of 

 the waves just spoken of, in the pulse-trace under consideration, are very 

 obscure in their origin, and are inconstant in their occurrence, sometimes being 

 more numerous than in the trace shown in Figure 111, and sometimes failing 

 altogether to appear. 



The Dicrotic Wave. The oscillation of pressure, however, which pro- 

 duces the middle wave of each of the pulsations of Figure 111, is so constant 

 in its occurrence that it is undoubtedly a normal and important phenomenon, 

 although, in different sphygmograms, the height, and position in the trace, of 

 the wave inscribed by this oscillation may vary. Occasionally this oscillation 

 is morbidly exaggerated, so that it may be not only recorded by the sphygmo- 

 graph, but even felt by the finger, as a second usually smaller up-stroke of 

 the pulse. In such a case the artery is felt to beat twice at each single beat 

 of the ventricle, and is said, technically, to show a " dicrotic " ' pulse. Where 

 a dicrotic pulse can be detected by the finger, it is apt to accompany a mark- 

 edly low mean tension of the arterial wall. The dicrotic pulse was known, 

 and named, long before the sphygmograph revealed the fact that the^ pulse is 

 always dicrotic, although to a degree normally too slight for the finger to 



1 From d/Kporoc, double-beating. 



