

THE EVENTS OF THE HUMAN CARDIAC CYCLE 105 



If the view is accepted that both are contributory causes, not 

 only do many of the apparently discordant observations assume 

 an aspect of greater harmony, but the occasional division of the 

 wave at or about the time of S.C. closure is no longer difficult to 

 appreciate. 1 



(d) The First and Second Negative Waves, or "x" and 

 "x"' Depressions. The two first depressions of auricular and 

 jugular tracings may be considered together, for the line of 

 descent is usually continuous, and is but broken by the second 

 positive or " c " wave. The complete depression commences 

 with the relaxation of the auricle, 2 and is continued well into 

 the systolic plateau. The fall in pressure is a marked one, and 

 attracted much attention from earlier writers, for it causes a 

 collapse of the veins of the neck. Hunter ( M ) regarded systole 

 of the ventricle as a valuable aid to the filling of the auricle, by 

 the creation of a partial vacuum in the chest. This view was 

 readvanced by Briicke and Mosso. Fran9ois-Franck performed 

 some experiments with a schematic apparatus to demonstrate its 

 possibility. But Fran9ois-Franck himself, and also Gottwalt and 

 Riegel, clearly showed that it is a factor of little importance, for 

 the fall remains after the chest is opened. Nevertheless it cannot 

 be denied that it contributes, for the systole of the ventricle pro- 

 duces a fall of intra-pleural pressure, which may be recorded by a 

 manometer in connection with that cavity. It is certain that it 

 is not the main cause of the fall. 



Active relaxation of the auricle has never been demonstrated, 

 and its enlargement in the normal chest is attributable at its 

 onset to the low pressure in the chamber surrounding it (Francois- 

 Franck). But the auricular relaxation is in itself insufficient to 

 account for the complete fall, 3 though it suffices to explain that 

 portion of it which occurs before the commencement of ventricular 



1 Bard finds this notch so constantly that he considers, and perhaps with justi- 

 fication, that the origin of the separate portions of the wave should be separately 

 discussed. It must be noted that Bering and Rautenberg strenuously deny the 

 intervention of the second factor. 



Porter gives the third positive wave a pressure value of 5 mm. Hg. 



1 Porter found that it occurred, as a rule, a little before relaxation of the 

 auricular appendix. This writer estimates the value of the complete fall at - 10 

 nun. Hg. 



* Frederick's tracings, with intact chest wall, in which auricle and ventricle 

 were dissociated. 



