THE PUMPING ACTION OF. THE HEART 153 



of these vessels to come together rather than produce a movement of the 

 blood contained in them. The negative pressure of the heart can not 

 therefore be of much consequence in attracting the venous blood into the 

 ventricle. 



Several factors may cooperate to produce this negative pressure, 

 among which may be mentioned the sudden opening out of the base of 

 the ventricles at the beginning of diastole, the recoil of the elastic tissue 

 which becomes compressed in the heart walls during systole and the 

 turgescence of the walls of the ventricles produced by the sudden inrush 

 of blood into the coronary vessels at the beginning of diastole. These 

 processes tend to cause an opening out of the Avails of the ventricles with 

 a consequent increase in the capacity of their cavities. 



The Auricular Curve 



Examination of the intraauricular pressure curve is of particular in- 

 terest because of the relationship which it has to a tracing taken of the 

 movements in the jugular vein at the root of the neck (see page 285). 

 This jugular pulse curve, as it is called, is produced mainly by the 

 changes of pressure occurring in the auricle, from which it differs only in 

 the relative height of the various waves. By graduating the intra- 

 auricular pressure curve by the method described above, we can tell 

 exactly the magnitude in the changes of pressure occurring during each 

 cardiac cycle. This obviously can not be done with a tracing taken from 

 the jugular vein, although qualitatively the tracings reflect exactly the 

 changes that are occurring in the auricle. 



On examining the auricular pressure curve (consult Fig. 34), we 

 find that after the wave of presystole, which of course corresponds exactly 

 with that on the intraventricular curve, a second wave occurs culminating 

 in a peak almost exactly at the beginning of the sphygmic period. The 

 curve then rapidly descends, usually indeed below the line of zero pres- 

 sure, and slowly rises throughout the rest of ventricular systole, until 

 the moment of opening of the auriculoventricular valve, when it descends 

 again and thereafter runs parallel with the ventricular curve. The let- 

 ters used to designate the waves are the same as those employed for 

 similar w r aves shown on the jugular pulse tracing, and although the 

 lettering is more or less arbitrary, we must accept it because of its gen- 

 eral usage in all work of this kind. 



As to the causes of the waves, A, is of course caused by auricular systole 

 or presystole; C, occurring as it does at the beginning of the period of 

 ventricular systole, is caused by the bulging into the auricle of the closed 

 auriculoventricular valve. The floor of the auricle, in other words, at 



