THE TIME OCCUPIED BY THE CARDIAC MOVEMENTS. 85 



systole, the curve falls rapidly, as the ventricle rapidly becomes relaxed. 

 In the descending part of the curve, at d and e, are two elevations, 

 which occur simultaneously with the second sound. These are caused by 

 the sudden closure of the semi-lunar valves, which, occurring suddenly, 

 is propagated through the axis of the ventricle to its apex, and thus 

 causes a vibration of the intercostal space; d corresponds to the 

 closure of the aortic valves, and e to the closure of the piilmonary 

 valves. The closure of the valves in these two vessels is not simul- 

 taneous, but is separated by an interval of 0'05 to 0'09 sec. The 

 aortic valves close sooner on account of the greater blood-pressure 

 there (Landois, 1876, Ott and Haas, Malbranc, Maurer, Griitzner, 

 Langendorff, v. Ziemssen, and Ter Gregorianz). 



Complete diastolic relaxation of the ventricle occurs from c to / in 

 the curve. It is clear, then, that the cardiac impulse is caused chiefly 

 by the contraction of the ventricles, while the auricular systole and the 

 vibration caused by the closure of the semi-lunar valves are also con- 

 cerned in its production. 



51. The Time Occupied by the Cardiac 



Movements. 



Methods. The time occupied by the various phases of the movements of the 

 heart may be determined by studying the apex-beat curve. 



(1.) If we know at what rate the plate on which the curve was obtained moved 

 during the experiment, of course all that is necessary is to measure the distance, 

 and so calculate the time occupied by any event (see Pulse). 



(2.) It is preferable, however, to cause a tuning-fork, whose rate of vibration 

 is known, to write its vibrations under the curve of the apex-beat, or the 

 curve may be written upon a plate attached to a vibrating tuning-fork (Fig. 

 25a, D, E). Such a curve contains fine teeth, caused by the vibrations of the 

 tuning-fork. D and E are curves obtained from the cardiac impulse in this way 

 from healthy students. In D the notch d, is not indicated. Each complete 

 vibration of the tuning-fork, reckoned from apex to apex of the teeth = 0'01613 

 sec., so that it is simply necessary to count the number of teeth and multiply to 

 obtain the time. The values obtained vary within certain limits even in health. 



Pause and Contraction of Auricles. The value of a b = pause + con- 

 traction of the auricles is subject to the greatest variation, and depends 

 chiefly upon the number of heart-beats per minute. The more quickly 

 the heart beats, the smaller is the pause, and conversely. In some 

 curves, even when the heart beats slowly, it is scarcely possible to 

 distinguish the auricular contraction (indicated by a rise) from the 

 part of the curve corresponding to the pause (indicated by a horizontal 

 line). In one case (heart-beats 55 per minute) the pause = 0'4 sec., the 

 auricular contraction = (H77 sec. In Fig. 25, A, the time occupied by 

 the pause + the auricular contraction (74 beats per minute) = 0'5 sec. 



