THE PHENOMENA NOTED DURING EACH CARDIAC CYCLE 305 



cardiac musculature is of as great importance as its force of contrac- 

 tion. Thus, a rapid heart may fail at times to eject a larger quantity 

 of blood than a slow one, because the length of time allotted to it for its 

 filling, is too brief. Quite similarly, a slowly beating organ may 

 succeed at times in furnishing a perfectly adequate supply of blood, 

 because it is able to relax more fully each time and to take in a corre- 

 spondingly larger amount of blood. Under normal conditions, the out- 

 put of the left ventricle equals that of the right. It might also be 

 mentioned that these chambers are not emptied entirely with each 

 systole, but that a small amount of ''residual" blood is always caught 

 in the recesses behind the different valve flaps. 



While certain unavoidable difficulties in the methods make it im- 

 possible to present exact values regarding the cardiac output, it may be 

 concluded that the average ventricular discharge per kilo of the body 

 weight is somewhat greater in small animals than in large. In the 

 dog, for example, values ranging between 50 and 90 c.c. have been 

 obtained. The ventricular output in a man weighing 70 kilos, has 

 been calculated at 87 grams with a cardiac frequency of 72 in a minute, 

 but this value is probably somewhat too high. In accordance with 

 the total quantity of blood present in the body, it has been calculated 

 that 4.5 kilos of blood are propelled during 72 cardiac cycles and hence, 

 62.5 grams or about 60 c.c. of blood are ejected during each systole. 



The Time Relation of the Cardiac Cycle. — Each cardiac cycle 

 begins with the contraction of the auricles, these chambers being 

 activated at practically the same time. It will be remembered, 

 however, that the excitation-wave begins at the venous vestibule on 

 the right side and hence, it has been possible to demonstrate that the 

 left auricle lags behindlthe right by a fraction of a second. Fredericq, ^ 

 who has determined this interval by exact graphic measurements, 

 states that its duration is 0.01-0.03 sec. 



The systole of the auricles is followed after an interval of 0.1 sec. 

 by that of the ventricles. Obviously, this time is required for the pas- 

 sage of the wave of excitation through the bundle of His, but as the 

 stimulus is distributed with equal rapidity to the different regions of 

 the ventricles, these chambers are activated at practically the same 

 time.^ The essential fact to remember, therefore, is that the auricular 

 cycle precedes the ventricular by about 0.1 sec. and hence, the ante- 

 chambers complete their systole before the contraction of the main 

 chambers actually begins. 



If the cardiac rate is 70 in a minute, the systole of the auricles 

 consumes 0.1-0.17 sec. and that of the ventricles 0.37 sec. Under the 

 same conditions the diastole of the former occupies 0.76-0.69 sec, 

 and that of the latter 0.48 sec. Thus, if the duration of each cardiac 

 cycle is taken to be 0.8 sec, it may be said in a general way that the 



1 Arch, intern, de physiol., 1906, 57. 



^ Slight dissociations have been observed at times in disease, due probably 

 to effects of blocking in the realm of the ventricular conducting paths. 

 20 



