9 8 



THE CIRCULATION OF THE BLOOD AND LYMPH 



The Auricular (and Venous) Pressure-Curve. The fluctuations of 

 pressure in the auricles, although confined within narrower limits 

 than in the ventricles, are of equal interest. They have been studied 

 in considerable detail both in animals and by indirect methods in 

 No fewer than three distinct elevations or ' positive waves,' 



man. 



separated or followed by three depressions or ' negative waves,' 

 have been described on the curve of intra-auricular pressure. 



The first elevation corresponds to the systole of the auricle. The 

 second coincides with the onset of the ventricular systole, and is 



Fig. 34. Schematic Comparison of Pressure Curves in the Auricle (or Superior 

 Vena Cava), the Ventricle and the Aorta in the Dog (Fredericq). In the auricular 

 curve are to be distinguished ab, the first positive or presystolic wave, corre- 

 sponding to the auricular systole (a wave) ; bb' or be, second positive wave or 

 first systolic wave, which corresponds with the beginning of the ventricular 

 systole (c wave); b'cd, the steep negative wave of which the beginning corre- 

 sponds to the opening of the semilunar valves; def, the third positive wave 

 (v wave), more or less serrated, ending at/, the point of opening of the auriculo- 

 ventricular valves; fg, a negative wave corresponding to the relaxation of the 

 ventricle. The time is indicated along the abscissa in tenths of a second, the 

 pressure along the vertical axis at the left in mm. of mercury. 



probably due to the sudden bulging of the auriculo- ventricular valve 

 into the auricle, or even to a slight regurgitation of blood from the 

 ventricle through the valve before it has completely closed. The 

 cause of the third elevation, which occurs during the period occupied 

 in the ventricular pressure-curve by the plateau, is less clearly made 

 out. In man, the events taking place in the right auricle during its 



