

THE EVENTS OF THE HUMAN CARDIAC CYCLE 97 



representative of volumes (Bard ia ) ; it is possible that a careful 

 comparison of curves obtained by the two methods might throw 

 some light on the subject. 



But whatever its method of propagation, the main fact rests 

 on an assured basis ; the wave may be taken as an indication of 

 auricular contraction. 1 



(b) The Second Positive or "c" Wave. The discussion 

 which centres around this wave involves many questions of 

 considerable intricacy. 



It is sometimes held that no such wave occurs in the curve of 

 intra-auricular pressure, but the tracings of Porter and Fredericq 

 demonstrate it too clearly and constantly to allow of doubt. 

 While the weight of evidence is in favour of its presence, yet Frey 

 and Krehl fail to show its presence in their tracings, and recently 

 Hering ( 23a ) has published a similar curve. Hering's experiments 

 were performed under perfusion ; the chest wall was removed ; 

 and the conditions generally were of an extremely artificial 

 character. 2 



In man its presence is attested not by the jugular curves so 

 much as by the oesophageal, and the results of such observations 

 warrant the statement that it is a normal event of the human 

 intra-auricular pressure curve. 



It is timed by all those who admit its occurrence as commencing, 

 in the auricle with ventricular -systole. According to Fredericq 

 the wave persists when by faradisation the auricle is caused to 

 fibrillate, and when the chest is opened. It disappears when the 

 ventricle ceases to beat. The wave must consequently have its 

 origin in ventricular systole. 3 



It is often held to originate in the bulging of the auriculo- 

 ventricular valves, at the onset of the systole (Chauveau, Fredericq, 

 and Porter). Chauveau in examining the heart of a living horse 

 (Chauveau and Faivre 6 ) inserted his finger into the beating 



1 Porter estimated the auricular pressure in the dog during auricular contraction 

 at 9 mm. Hg. This and other auricular pressures are given by Porter at page 633, 

 and will be subsequently quoted. They are the pressures from one curve. 



1 Moreover it must be stated that Hering ( 23c ) firmly believes in the presence 

 of this wave in the auricular pressure curve. He has recently commented upon 

 the reference to his own curve and also that of Cushny and CJrosh, published by 

 Mackenzie ("*). 



* Similar experiments have been )>crformed by Fredericq with the chest wall 

 intact, either by vagal stimulation, or by stimulating through the chest wall. 



G 



