154 DURATION OF THE CARDIAC PHASES. [ BoOK T - 



During the expansion of the artery and probably for some little 

 time beyond, viz. up to the occurrence of what in speaking of the 

 pulse-wave we shall callthe dicrotic notch, blood is being propelled 

 from the ventricle. By measuring this time or by deductions from 

 the curve of the cardiac impulse, it has been concluded that the time 

 during which blood is escaping from the ventricle or the duration 

 of the second phase of the ventricular systole, amounts to about 

 O'l sec. 



Deducting these two periods from the total period of 0'3 sec., 

 there would be left a period of O'l 15 sec., marking the third phase 

 of the systole, during which the ventricle, though empty, is con- 

 tinuing its contractions. Upon the view however that the closure 

 of the valves does not mark the end of the systole, this phase 

 must be taken as still longer. 



In a heart beating 72 times a minute, which may be taken as 

 the normal rate, each entire cardiac cycle would last about 0'8 sec., 

 and taking 0'3 sec. as the duration of the systole, the deduction of 

 this would leave 0'5 sec. for the whole diastole of the ventricle 

 including its relaxation. 



At the close of this period, there occurs the systole of the 

 auricles, the exact duration of which it is difficult to determine, it 

 being hard to say when it really begins, but which perhaps may 

 be taken as lasting on an average O'l sec. The systole of the 

 ventricle follows so immediately upon that of the auricles, that 

 practically no interval exists between the two events. 



We may sum up therefore the details of the duration of the more 

 important phases of the cardiac cycle in the following tabular form. 



sees. sees. 

 Systole of ventricular previous to ~\ 



opening of semilunar valves . 0'085 

 Escape of blood into aorta . . O'lOO !- 

 Continued contraction of the 



emptied ventricle . . . O'lloj 

 Total systole of the ventricle . . 0'3 

 Diastole of both auricle and ven- 1 



tricle or "passive interval" . 0'400 j> 

 Systole of auricle . . . O'lOO J 



Sum of above two, making the 

 diastole of ventricle or "pause" 

 between second and first sound . 0'5 



Total Cardiac Cycle . . . .; (^8 

 Or selecting only the important facts out of the -$ sec. occupying 

 the whole canfiac cycle, -^ sec. or possibly rather more are taken up 

 by the systole, and T % sec. or possibly rather less by the diastole of 

 the ventricle. 



The following diagram may be useful as giving in a graphic 

 form a general idea of the sequence and duration of the several 



