THE DICROTIC WAVE. 



in 



semilunar valves is greatly enfeebled. On a review of the whole 

 evidence, the central origin of the dicrotic wave must be taken as an 

 assured fact. 



Reflected waves, however, if synchronous in time, may possibly 

 modify the dicrotic wave, and, according to the sign of these waves, 

 the height of the dicrotic wave may be diminished or increased in 

 different arteries ; the time relations of the dicrotic wave to the primary 

 wave may also be altered thereby. 



The question of interference between reflected waves and the 

 primary pulse waves is inextricably complicated, owing to the fact 

 that it is necessary to take into account not only the centripetal 

 reflected waves which arise in the peripheral field of an artery, but 

 also the reflected waves which arise in other arterial fields, and 

 which, after being again centrally reflected, course centrifugally down 

 the observed artery. 



That the pulse wave is affected by purely local conditions, is shown 

 by the following facts : 



1. The primary and dicrotic waves of the radial pulse are greatly 

 diminished by occlusion of the veins of the arm, by the dependent 

 position of the limb, or by plunging the arm into cold water. 



2. They are greatly increased when the arm is elevated above 

 the head, or plunged into hot water. 1 



When the general and not the local conditions of the circulation are 

 varied, the dicrotic wave is found to be 

 most marked in the following condi- 

 tions : 



1. When the arterioles are dilated, the 

 arterial tension low, and the systole of 

 the heart vigorous; for example, after 

 a hot bath, or in the first stage of asthenic 

 fever. 



2. When the systolic output of the 

 left ventricle is, from any cause, dimin- 

 ished; for example, on taking a deep 

 inspiration, in the second stage of a 

 forcible expiratory effort, and after severe 

 haemorrhage. 



The dicrotic wave is most marked in 

 youth when the arteries are elastic. In 



any individual it is increased at times of ^ 



exhaustion, and diminished in times of oa ^ 



vigour. The amplitude of the dicrotic ' ' " ' ' ' ' 



6 , T i -,', FIG. 76. Six curves taken during 



wave, so long as the local conditions are the escape of the heart fror g 

 not varied, can be taken as a sign of low vagal inhibition. v. Frey. 

 arterial tension. 



The predicrotic wave, which is sometimes observed preceding the 

 dicrotic wave, is, according to v. Kries, due to reflection for a com- 

 parison of the pressure and velocity curves shows that, at the point of 

 occurrence of this wave, the pressure and velocity are most divergent. 

 If the predicrotic wave become very marked, it may rise to a higher 

 elevation than the primary wave. The pulse curve is then marked 

 by an anacrotic wave. The curve is anacrotic in type when the 



1 Hill, Barnard, and Sequeira, Journ. PhysioL, Cambridge and London, 1897, vol. xxi. 



