CH. XXI.] THE PULSE-TKACING 291 



elevation. The production of the dicrotic wave is favoured by a 

 low blood-pressure when the heart is beating forcibly, as in fever. 

 Such a pulse is called a dicrotic pulse (fig. 292), and the second beat 

 can be easily felt by the finger on the radial artery. 



The percussion wave is produced by the ventricular systole 

 expanding the artery. The sharp top at its summit is due to the 

 sudden upward spring of the light lever of the sphygmograph. If it 

 were possible to obtain a true record 

 of what really occurs, we should 

 doubtless have a tracing as shown 

 by the continuous line in the 

 accompanying figure (fig. 293). The 

 apex of the tidal wave, B, marks the FIG. 292.-Dicrotic pulse. 



end of the ventricular systole. 



In our study of intra-cardiac pressure, we saw that the systolic 

 plateau sometimes has an ascending, sometimes a descending, slope 

 (see p. 243) ; we now come to the explanation of this fact. If after 

 the first sudden rise of pressure in the aorta the peripheral resistance 

 is low, and the blood can be driven on from the aorta more rapidly 

 than it is thrown in, the plateau will sink. If, on the other hand, 

 the peripheral resistance is high, the aortic pressure will rise as long 

 as the blood is flowing in, and we get an ascending systolic plateau 

 and an anacrotic pulse. Thus an anacrotic pulse 

 is seen in Bright's disease, where the peripheral 

 resistance is very high. 



If a long pulse-tracing is taken, the effect of 

 the respiration can be seen causing an increase of 

 pressure, and a slight acceleration of the heart's 

 beats during inspiration. 



The main waves of the pulse can be demon - 

 tidai ; r, strated without the use of any instrument at all 



dicrotic ; aud D, post- . J 



dicrotic waves. by allowing the blood to spurt from a cut artery 



on to the surface of a large sheet of white paper 

 travelling past it. We thus obtain what is very appropriately called 

 a licemautograpli (fig. 294). 



A distinction must be drawn between the pulse as felt at any 

 one spot in the course of an artery, and the pulse-wave which is 

 propagated throughout the arterial system. This wave of expansion 

 travels along the arteries, and is started by the propulsion of the 

 contents of the left ventricle into the already full arterial system. 

 The more distant the artery from the heart, the longer the interval 

 that elapses between the ventricular beat and the arrival of the 

 pulse-wave. Thus it is felt in the carotid earlier than in the radial 

 artery, and is still later in the dorsal artery of the foot. The 

 diff jrenco of time is, however, very slight ; it is only a minute frac- 



