MECHANICS OF THE HEART-BEAT 



99 



systole can be followed to some extent by recording the venous pulse 

 in the jugular veins, especially the internal jugular, at the root of the 

 the neck (Fig. 36). Successful tracings can be obtained, not only in 

 certain pathological conditions, but in many normal individuals, and 

 it is probably only a matter of improved technique to obtain them 

 in all. The jugular venous pulse-tracing, like the intra-auricular 

 pressure-curve, shows in general three well-marked elevations and 

 three depressions, and there is good evidence that, broadly speaking, 

 these features of the jugular curve corre- 

 spond as regards their origin with the 

 changes of pressure in the auricle. 



Identical features are observed on records 

 of the normal venous pulse taken from veins 

 of dogs near the heart, and on records of the 

 pulse taken by a sound in the oesophagus. 

 The oesophagus pulse is related to the pul- 

 sation of the left auricle, the venous pulse to 

 the changes of pressure in the right auricle. 

 The first elevation, called the a (auricular) 

 or p (presystolic) wave, begins with, and is 

 the result of, the auricular systole. It is 

 probably produced by stasis in the veins due 

 to the contraction of the auricle, as well as 

 to the effect of the impact of the auricular 

 systole. The downstroke on the curve which 

 succeeds this first elevation corresponds to 

 the first negative wave or presystolic fall, 

 which is due to the auricular relaxation . This 



Fig- 35. Schema of Events in the Cardiac Cycle, 

 in Relation to the Venous Pulse (Ewing). i, Tracing 

 from Vena Cava, showing presystolic rise and fall, 

 PR, PF (a wave) ; SR, systolic rise and fall 

 (c wave); O', first onflow wave and, DR. diastolic 

 rise and fall (v wave); O*, second onflow wave; 

 2, auricular myogram (tracing of contraction of 

 auricle); 3, ventricular myogram (tracing of con- 

 traction of ventricle); 4, record of the movement 

 of the auriculo-ventricular septum; 5, ventricular 

 volume curve (plethysmographic curve of dis- 

 charge of the ventricles) ; 6, curve of aortic pressure ; 

 7, intraventricular pressure -curve. 



fall of pressure is terminated by a rise the second positive wave which 

 begins at the same moment as the ventricular systole, and is the ex- 

 pression on the venous pulse-curve of that second elevation of the 

 intra -auricular pressure whose probable cause has already been found 

 in the sharp protrusion of the auriculo-ventricular valve into the 

 auricular cavity under the stress of the ventricular systole while the 

 semilunar valve are still closed. In addition to the actual bulging of 

 the auriculo-ventricular valves, the impact of the sudden contraction 

 of the ventricle on its contents transmitted through the valve to 

 the contents of the auricle may aid in producing the rise of venous 

 pressure. The second elevation has been termed the c wave by certain 



