526 CIRCULATION OF BLOOD AND LYMPH. 



the pressure changes in the heart, and affords a valuable means 

 of diagnosis in cases of valvular lesions and other pathological 

 conditions of the heart. It is evident also that the venous pulse 

 gives a ready means of determining the rate of beat of the auricles, 

 just as the arterial pulse enables us to count the beats of the ven- 

 tricles, and in this way records of the venous pulse are important 

 in the interpretation of irregularities in the beat of the heart 

 (arrhythmia). 



As usually recorded the venous pulse shows three positive 

 waves, designated commonly as the a, c, and v waves, and three 

 negative waves. Of the three positive waves, the a wave marks, 

 undoubtedly, the contraction of the auricle, but in order to 

 locate this wave or, indeed, to interpret at all the complicated 

 venous pulse, it is necessary to have a simultaneous tracing of 

 the arterial pulse, preferably the carotid, or of the apex beat of 



Fig. 217. — Simultaneous tracings of the carotid and venous pulses. In tlie venous 

 tracing (internal jugular) a indicates the auricular wave due to the contraction of the auri- 

 cle; c is the carotid wave due (Mackenzie) to an impulse from the neighboring carotid 

 artery; v is the ventricular wave due to the checking or stagnation of the flow into the 

 auricle as this chamber fills during the period of closure of the auriculoventricular valves. 

 — {Mackenzie.) 



the heart. Either of these latter tracings enables one to mark 

 upon the venous pulse the point at which the ventricular systole 

 begins, and the wave immediately preceding this point must 

 be due to the auricular contraction, the a wave (Figs. 217 and 

 218). Following the rise of the a wave there is a fall, the first 

 negative wave, which is due to the auricular relaxation. The 

 interpretation of the other two positive and negative waves 

 has been the subject of much discussion. Mackenzie, one of 

 whose tracings is reproduced in Fig. 217), believed that the 

 c M'ave is due simply to the pulse in the underlying carotid or 

 subclavian artery, and that, therefore, it has no special significance 

 in regard to changes within the auricle itself. Discussions in re- 

 gard to the meaning of this wave have turned largely upon its time 

 relations to the pulse wave in the neighboring arteries. Some ob- 

 servers have obtained records which seem to shoAV that the c wave 



