THE CIRCULATION OF THE BLOOD 



289 



Though the numerical values given for the duration of the auricular and 

 ventricular systole and diastole, viz.: auricular systole o.io second; auricular 

 diastole 0.70 second; ventricular systole 0.33 second; ventricular diastole and 

 pause 0.47 second, it must be borne in mind that they are true only for the 

 heart beating approximately 75 times per minute. If the number of beats 



AUKICUL/IK D/AS/ULL 



.C7.osu.re of 

 iLricv2o-ventricu.la.r 

 valve. 



4 . .3 4 .S .6 .r .8 .i .% 



FIG. 127. A SCHEMATIC REPRESENTATION OF THE EVENTS OF A CARDIAC CYCLE. 



increases, not only does the entire cycle diminish in duration, but its dif- 

 ferent subdivisions, auricular systole, ventricular systole, and diastole also 

 diminish in duration, though in unequal degrees. Thus it has been de- 

 termined that with each increase of 10 beats above 70, the ventricular systole 

 shortens by about 0.02 second and the ventricular diastole by about o.io 

 second. The opposite holds true if the num- 

 ber of beats decreases below 70 per minute. 

 The Relation of the Cardiogram to the 

 Events of the Cardiac Cycle. A compari- 

 son of a typical cardiogram, such as is seen 

 in Figs. 116 and 128, with the curve of intra- 

 ventricular pressure, shows that they corre- 

 spond in essential features. The slight eleva- 

 tion (a) on the cardiogram represents the 

 contraction of the auricle, which completing 



f 



e 



c 0' C'o 



FIG. 128. CARDIOGRAM, 



the filling of the ventricle Causes it to press ricular systole; 6,^ rf, ventricular sys- 

 . c , . , , 11 7 tole; a, e. ve 



o, Au- 

 ar sys- 

 . , . , , 11 7 , . ventricular diastole; C.O, 



more vigorously against the chest wall; b-c c i osing and opening of the auriculo- 



representS the contraction of the ventricles, ventricular valves; O', C', opening and 



at which moment the apex is suddenly and ^j^^&& 



forcibly dnven against the chest wall; C-d ventricular discharge ;CC', time of the 



represents the systolic plateau, the time dur- occurrence of the first and second 

 ing which the ventricle is discharging blood s respectively. 

 into the aorta ; d-e represents the relaxation of the ventricle, while e-f rep- 

 resents the time of the diastole during which the heart cavities are enlarg- 

 19 



