ORIGIN OF THE DICROTIC WAVE. 103 



and absent in the others, while the base line is uneven. In mitral stenosis the amount of blood 

 discharged into the left ventricle frequently varies, hence the variations in the characters of 

 the arterial pulse.] 



There may be other secondary waves iri the lower part of the descent. 



[Respiratory or Base Line. If a line be drawn so as to touch the bases of all 





Fig. 82. 

 Irregular pulse of mitral regurgitation. 



the up-strokes, we obtain a. straight line, hence called by this name. The base line 

 is altered in disease and during forced respiration ( 74).] 



The pulse-curve indicates the variations of pressure which the blood exerts on the arterial 

 walls, for the lever rises and falls with the pressure, hence v. Kries calls it the "pressure-pulse." 



68. ORIGIN OF THE DICROTIC WAVE. The dicrotic or recoil wave, 



which is always present in a normal pulse, is caused thus : During the ventricular 

 systole a mass of blood is propelled into the already full aorta, whereby a positive 

 wave is rapidly transmitted from the aorta throughout the arterial system, even to 

 the smallest arterioles, in which this primary tvave is extinguished. As soon as the 

 semi-lunar valves are closed, and no more blood flows into the arterial system, the 

 arteries, which were previously distended by the mass of blood suddenly thrown 

 into them, recoil or contract, so that in virtue of the elasticity (and contractility) of 

 their walls, they exert a counter-pressure upon the column of blood, and thus the 

 blood is forced onwards. There is a free passage for it towards the periphery, but 

 towards the centre (heart) it impinges Upon the already closed semi-lunar valves. 

 This develops a new positive wave, which is propagated peripherally through the 

 arteries, where it disappears in their finest branches. In those cases where there is 

 sufficient time for the complete development of the pulse-curve, (as in the short 

 course of the carotids, and in the arteries of the upper arm, but not in those of the 

 lower extremity, on account of their length), a second reflected wave may be caused 

 in exactly the same way as the first. Just as the pulse occurs later in the more 

 peripherally placed arteries than in those near the heart, so the secondary wave 

 reflected from the closed aortic valves must appear later in the peripheral arteries. 

 Both kinds of waves, the primary pulse-wave, the secondary, and eventually even 

 the tertiary reflected wave arise in the same place, and take the same course, and 

 the longer the course they have to travel to any part of the arterial system, the 

 later they arrive at their destination. 



[The conditions which favour dicrotism are low blood-pressure and a rapid sharp cardiac con- 

 traction. When the blood-pressure is low, there is less resistance to the inflow of blood at the 

 aorta from the left ventricle, so that its systole occurs sharply, forcing on the blood and distending 

 the arterial walls. The elastic -coats rebound on the contained blood, and thus start a wave from 

 the closed semi-lunar valves.] 



The following points regarding the dicrotic wave have been ascertained experi- 

 mentally, chiefly by Landois : * 



1. The dicrotic wave occurs later in the descending part of the curve, the further 

 the artery experimented upon is distant from the heart. Compare the curves, 

 fig. 83. 



The shortest accessible course ispthat'of the carotid; where the dicrotic wave reaches its 

 maximum 0*35 to 0*37 sec. after the beginning of the pulse. In the upper extremity the apex 

 of the dicrotic wave is 0*36 to 0*38 to 0*40 sec. after the beginning of the pulse-beat. The 

 longest course is that of the arteries of the lower extremity. The apex of the dicrotic wave 



