THE EVENTS OF THE HUMAN CARDIAC CYCLE 89 



and carotid tracings must be judged on their merits. The dis- 

 crepancies in the findings are greater in the case of jugular curves 

 than they are in the case of the auricular. Considerable confusion 

 appears to exist as to the events occurring in that portion of the 

 heart's cycle which lies between the closura of the semilunar valves 

 and the opening of the tricuspids. Further work is needed, and 

 the first appeal must obviously be to experiments upon the time 

 relations of the venous curve in animals. But though there are 

 differences of opinion, it must be understood that they are in the 

 main of a minor character, and their complete elucidation is 

 chiefly necessary that the origin of the waves may be accurately 

 determined. The differences which have so far arisen are, in 

 other words, of such a nature as to in no way invalidate the 

 information which can be obtained at the bedside. 



The majority of writers are agreed in timing the commence- 

 ment of the " c " wave in man as synchronous or almost syn- 

 chronous with the primary wave of the carotid at the same level 

 of the neck. Fredericq ( 12c ), moreover, has recently shown them 

 to be simultaneous in the carotid and jugular of the dog. For 

 practical purposes the two waves may be taken as starting 

 together, but the actual evidence for their absolute synchronicity 

 is perhaps not convincing. In certain instances Fredericq found 

 a slight deviation, and Bard ( lb ) has obtained similar results 

 in man. 1 



The " a " wave and " x " depression have together a duration 

 of i to 1 sec. (Mackenzie, Gibson ( 18 ), and many other writers), 

 and constitute the a-c interval. This a-c interval, the time dis- 

 tance between the beginnings of the waves representing the com- 

 mencement of auricular and ventricular systole, is taken as a 

 measure of the function of the heart in respect of the conduction 

 of impulses from auricle to ventricle, and is of great clinical 

 importance. 



Over the relations of the " v " wave there is some difference 

 of opinion, and this apparently for several reasons. In the first 

 place, it shows considerable variation in form ; it may show a 

 division into two ; it assumes an entirely new outline and new 



1 Bard's tracings ( lb ) are not beyond criticism. It is not expressly stated that 

 the jugular and carotid curve's were taken at the same level in the neck, and the 

 dfvi.ition might be attributable to transmission delay. Professor Bard has recently 

 published further notes ( lc ) on this subject Bachmauu has confirmed his results 

 (Amer. Journ, Med. Sci., vol. 136, 1908, p. 674). 



