86 TIME OCCUPIED BY THE VENTRICULAR SYSTOLE. 



In D the a 5=19 to 20 vibrations = 0' 3 2 sec.; in E= 2 6 vibrations 

 = 0-42 sec. 



Ventricular Systole. The ventricular systole is calculated from the 

 beginning of the contraction, b to e, when the semi-lunar valves are 

 closed ; it lasts from the first to the second sound. It also varies 

 somewhat, but is more constant. When the heart beats rapidly, it is 

 somewhat less during slow action, greater. In E = 0'32 sec.; in D 

 = 0'29 sec. ; with 55 beats per minute Landois found it = 0*34, with a 

 very high rate of beating = '19 9 sec. 



When the ventricle beats feebly, it contracts more slowly, as can be shown by 

 applying the registering apparatus to the heart of an animal just killed. In Fig. 

 27, from the ventricle of a rabbit just killed, the slow heart-beats, B, are seen to 

 last longest. 



Fig. 27. 



Curves obtained from the ventricle of a rabbit, and written upon a vibrating plate 

 attached to a tuning-fork (vibration = 0'01613 sec.) A, tolerably soon after 

 death ; B, from the dying ventricle. 



In calculating the time occupied by the ventricular systole we must remember 

 (1.) The time between the two sounds of the heart, i.e., from the beginning of the 

 first to the end of the second sound (b to e). (2.) The time the "blood flows into the 

 aorta, which comes to an end at the depression between c and d (in Fig. 25a, E). 

 Its commencement, however, does not coincide with b, as the aortic valves open 

 0'085 (Landois) to 0'073 (Rive) sec. after the beginning of the ventricular systole. 

 Hence the aortic current lasts 0'08 to 0'09 sec. 



This is calculated in the following way : The time between the first sound of 

 the heart and the pulse in the axillary artery is 0'137 sec., and of this time 0'052 

 sec. are occupied^in the propagation of the pulse-wave along the 30 cm. of artery 

 lying between the root of the aorta and the axilla. Thus the pulse- wave in the 

 aorta occurs 0'137 minus 0'052=0'085 sec. after the beginning of the first sound. 



The current in the pulmonary artery is interrupted in the depression between 

 d and e. (3.) Lastly, the time occupied by the muscular contraction of the 

 ventricle, which begins at b, reaches its greatest extent at c, and is completely 

 relaxed at/. The apex of the curve, c, may be higher or lower according to the 

 flexibility of the intercostal space, hence the position of c varies. In hypertrophy 

 with dilatation of the left ventricle, the duration of the ventricular contraction 

 does not greatly exceed the normal. 



The time which elapses between d and e, i.e., between the complete 

 closure of the aortic and pulmonary valves, is greater the more the 

 pressure in the aorta exceeds that in the pulmonary artery, as the 



