THE PUMPING ACTION OF THE HEART 153 



which is covered by a rubber diaphragm and connected with a large 

 tambour. The absence of any suction pressure in the heart shows that 

 its filling cannot depend, as does that of a mechanical pump, on aspira- 

 tion between each beat. This does not mean that there may not be a 

 slight suction pressure in the ventricle, as well as the auricle, during 

 the beginning of each inspiratory movement in the unopened thorax, 

 but since this pressure inside the ventricle must always be less negative 

 than that in the thoracic cavity it can participate in the filling of the 

 heart only to the small extent indicated on page 324. The rate of filling 

 of the ventricle depends primarily on the rate of flow in the great veins 

 leading to the heart (page 217). 



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 pressure curves of 

 which it differs only in the relative height of the various waves. By 

 graduating the intraauricular pressure curve by the method described 

 above, we can tell exactly the magnitude in the changes of pressure oc- 

 curring during each cardiac cycle. This obviously cannot be done with 

 a tracing taken from the jugular vein, although qualitatively the tracings 

 reflect 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 shortly after the beginning of the presphygmic period. The 

 curve rapidly descends during the first part of the sphygmic period and 

 then 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. 



There are therefore three positive waves on the curve, the first being 

 caused by auricular systole or presystole ; the second, by the closure and 

 possibly by bulging into the auricle of the auriculoventricular valve ; and 

 the third, by the gradual filling of the auricle from the veins. The 

 second wave corresponds to the wave C of the jugular pulse (page 286), 

 which would seem to show that this is a reflected auricular wave. The 

 depression following the second wave corresponds to wave X of the 

 jugular pulse and the lowering of pressure which it indicates is probably 

 '&ne to the cooperation of three forces, all tending to increase the auric- 

 rtlur capacity: (1) The diastole of the walls of the auricle; (2) the 



