THE CIRCULATION OF THE BLOOD AND LYMPH 89 



fact that on most of the endocardiac pressure tracings of the 

 best modern manometers, whether the curves belong to the type 

 of the peak or of the plateau, no sudden change of curvature, no 

 nick, or crease, or undulation reveals the moment of opening or 

 closure of any valve. But by experimentally graduating a pair 

 of elastic manometers, and obtaining with them simultaneous 

 records of the pressure in auricle and ventricle, or by using a 

 ' differential ' manometer, in which the pressures in two cavities 

 are opposed to each other, so that the movement of the membrane 

 corresponds to their difference, we can calculate at what points 

 of the ventricular curve the pressure is just greater than and 

 just less than the pressure in the auricle. The first point, it is 

 evident, will correspond to the instant at which the mitral or 

 tricuspid valve, as the case may be, is closed, and the second to 

 the instant at which it is 

 opened. And in like man- 

 ner, by comparing the 

 pressure-curve of the aorta 

 with that of the left ven- 

 tricle, the moment of open- 

 ing and closure of the semi- 

 lunar valves mav be de- 



, /T ^. , Ox FIG. 29. DIAGRAM OF CARDIAC SOUND FOR 



termmed (FlgS. 27 and 28). SIMULTANEOUS REGISTRATION OF ENDO- 

 According to the best ob- CARDIAC PRESSURE IN AURICLE AND VEN- 



servations, the closure of TRICLE. 



the semilunar valves takes A ' elastic ampulla for auricle ; V, for ven- 

 , ,. j tricle ; T, tubes connected with recording 



place at a time correspond- tambours 



ing to a point on the upper 



portion of the descending limb of the intraventricular curve. 



)n the blood-pressure curve of the aorta, simultaneously registered, 

 corresponding point is near the bottom of the so-called ' aortic ' 



On the blood-i 

 the 



notch (p. 96) which precedes the dicrotic elevation. For clinical 

 purposes, in man the moment of closure of the semilunar valves 

 (denoted by the abbreviation S.C. point) may be taken as 0^03 second 

 before the bottom of the aortic notch in sphygmographic tracings 

 from the carotid, this being approximately the average time taken 

 by the pulse-wave in travelling from 'the aorta to the carotid. The 

 S.C. point, the A.O. point, or moment of opening of the auriculo- 

 ventricular valves, and the beginning of the ventricular systole, are 

 three important points of reference in the measurement and inter- 

 pretation of pulse-tracings in clinical work. The A.O. point in man 

 may be taken as a point '0-03 second in advance of the summit of 

 the dicrotic wave ' on the carotid pulse-tracing (Lewis). But this 

 is the most difficult of the three standard points to determine 

 clinically with anything like accuracy. 



The study of the curves of endocardiac pressure enables us to 

 add precision in certain points to the description of the events 



