

THE EVENTS OF THE HUMAN CARDIAC CYCLE 90 



At the moment when the valves may be supposed to balloon 

 into the auricle, that chamber is rapidly enlarging, and it may be 

 held that any decrease in the capacity of the auricles from the 

 former source will be fully compensated by the dilatation of the 

 organ. But granted that a positive wave of pressure is started 

 by the tricuspid valves, 1 its appearance in a recognisable form upon 

 the curve of intra -auricular pressure will depend on the relation- 

 ship of the pressures represented in this wave and the pressures 

 produced by other influences tending to expand the auricle ; thus 

 there is no reason to deny the possibility of the appearance* of the 

 wave on the auricular pressure curve. Again its conduction into 

 the veins of the neck will depend on the relationship of the rate 

 at which the wave is propagated and the rate at which the blood 

 enters the auricle, and, assuming its origin in the auricle, there 

 is every reason to believe that this relationship is such as to allow 

 of conduction. 



From the collected evidence we may conclude that the second 

 positive wave is a real auricular event in man and that it may appear 

 in the neck as a component part of the jugular pulse. 



In considering the causal factors of the " c " wave in the neck 

 further complications arise. The shock of arterial pulsation may 

 be transmitted to the receiver, tor it occurs at or about the instant 

 when the " c " wave has its onset. There is also the possibility 

 of a direct conduction of the arterial pulsation, either aortic, in- 

 nominate, or carotid to the accompanying veins with which these 

 vessels are in contact. Each of these factors has been advocated 

 in turn as the chief element in the production of the " c " wave 

 (cp. Friedreich u , p. 289, Belski 4 ). The leading points and 

 arguments alone require consideration. 



It is held by Mackenzie, Gerhardt and Wenchebach that the 

 " c " wave is due to the impact of the neighbouring artery 2 alone. 

 Given in the main by Mackenzie, the chief evidence in favour of 



1 The origin of the second positive wave in the bulging of the auriculo-ventricular 

 valves cannot be regarded as proven, though it appears to be the most rational view 

 to hold of its production. Bering has convinced himself that it is iudej>endent of 

 the shock of the root of the aorta, and auricular branches of the same, by numerous 

 ex|>rriinental researches, but he does not detail the evidence ( tSc ). 



1 While the actual statement is frequently made that the impact is from the 

 carotid, yet it is understood that an arterial impact is intended, and that the 

 particular artery involved is that which lies in the neighbourhood of the receiver 

 by means of which the tracing is obtained. In the light of Keith's anatomio. 

 description it would appear that the artery is usually the subnlavian. 



