THE CIRCULATION OF THE BLOOD 



289 



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

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

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



l/RICVL A R ,D/A STOL 



'osurc ofScmi-luna? 

 valves 



... Opening of 

 ' ?lri 



valve. 



Closure or 

 ricttlo -ventricular 

 valve. 



HNTRICVLAR SYSTOW VtNTRICUTAR DIA 



Second^ 



J .2 .3 .4 .S .6 .7 .8 .1 .2 .3 



FIG. 130. A SCHEMATIC REPRESENTATION OF THE EVENTS or A CARDIAC CYCLE. 



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. 118 and 131, 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 

 the filling of the ventricle causes it to press 



c 11 I. IO1CJ U> t Cj VCUU.n-ui.aJ. viiaowix., \s,^s t 



more Vigorously against the Chest Wall j 0-C c i os ing and opening of the auriculo- 



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



i . , i jj i j closing of the semilunar valves; C, Cr, 



at which moment the apex is suddenly and period 6 of risin g tension; O'>, period of 



forcibly driven agaillSt the chest wall; C-d ventricular discharge ;CC', time of the 



represents the systolic plateau, the time dur- ^J s en ^ s e e v ^ 

 ing which the ventricle is discharging blood 



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

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

 ing with the incoming of a new volume of blood, in consequence of which 

 the heart is pressing against the chest walls. The systolic plateau is charac- 

 terized by one or more elevations and depressions, the true cause of which 

 is unknown. 



CO CO 



FIG. 131. CARDIOGRAM. 



f 



Au- 



