234 



PHYSIOLOGY. 



CARDIAC REVOLUTION OR CYCLE. 



A cardiac revolution or cardiac cycle shows that the heart- 

 muscle has alternate contractions and relaxations. The cycle means 

 that the heart at any particular time experiences certain changes 

 until it once more takes on the same condition that it had at the 

 time when the observation began. 



The right and left auricles contract at the same time forming 

 the auricular systole; this is succeeded by contraction at the same 

 time of the right and left ventricles; then the whole heart is in a 

 state of rest, a general relaxation or diastole. Then the revolution 

 again begins. 



I 



Diastole 



01 02 03 04 0-5 06 07 08 09 lOsecs. 



JHeart Sounds 



..... dup Lubb dup 



Fig. 69. A Cardiac Cycle. (STARLING.) 



The cardiac revolution may be divided as follows: (1) the first 

 sound; (2) the first, or short, silence; (3) the second sound; and, 

 (4) the second, or long, silence. 



If the cardiac revolution be divided into tenths, then the first 

 sound will be 4 / 10 ; the first silence, Y 10 ; the second sound, 2 / 10 ; 

 and the long silence, 3 / 10 . 



The time of the various acts of the total cardiac movement in 

 man are, according to Gibson, as follows: 



Auricular systole 0.112 second. 



Ventricular systole 0.368 second. 



Ventricular diastole 0.578 second. 



Cardiac cycle 1.058 seconds. 



