104 TIME-RELATIONS OF THE MOVEMENTS OF THE HEART. 



THE TIME-RELATIONS OF THE MOVEMENTS OF THE HEART. 



Method. The time-relations of the individual phases of the movements of 

 the heart can be most reliably discerned in the curves of the apex-beat : 



When the distance traversed at a uniform rate in a unit of time is known 

 for the registering surface, the time corresponding to each portion of the curve 

 can be ascertained by direct measurement (as in the case of pulse-curves) . 



Landois determined the time by having the curves traced on a tablet 

 vibrating on the arm of a large tuning-fork (Fig. 60) . The curve then contains in 

 all of its segments small undulations due to the vibrations of the tuning-fork. 

 In Fig. 28, D and E represent apex-beat curves of healthy students registered 

 in this way (in D the elevation d is not distinct). A complete vibration of the 

 tuning-fork (from the apex of one undulation to that of the next) corresponds 

 to 0.01613 second; by counting the number of undulations and multiplying by the 

 factor the time is obtained. Although there is a certain regularity in the time 

 of the individual phases of the movement, the readings nevertheless vary between 

 wide limits even in healthy individuals. 



The value of a b, which is equivalent to the pause plus the auricular 

 contraction, is subject to the widest variations and depends chiefly on 

 the frequency of the pulse ; for, the more rapidly the heart-beats follow 

 one another, the shorter, naturally, will be the pause, until it finally 

 disappears altogether. Even when the rate of the heart is slow, it is 

 often impossible to distinguish in the curve the portion corresponding 

 to the pause, which, owing to the gradual filling of the heart and the 

 resulting slight bulging of the intercostal space, has a gently ascending 

 form, from that due to the auricular contraction and appearing as a 

 hillock. In one case in which the heart-beats were 55 in a minute, 

 Landois found the pause to be 0.4 second and the auricular contrac- 

 tion 0.177 second. In Fig. 28, A, the pause plus the auricular con- 

 traction, when the heart beats 74 times in a minute, is found on 

 measurement to be 0.5 second. In D the corresponding period a b is 

 equivalent to from 19 to 20 vibrations, or 0.32 second; in E the period 

 is equivalent to 26 vibrations, corresponding to 0.42 second. 



The ventricular systole is estimated from b, the beginning of the 

 contraction, to e, the completed closure of the semilunar valves of the 

 pulmonary artery. It, therefore, extends from the first to the second 

 heart-sound. This period is also variable, though considerably more 

 constant. When the action of the heart is accelerated, the period 

 becomes less, when the action is slower the period increases; in E it is 

 0.32 second, in D 0.29 second; when the heart-beats were only 55 Lan- 

 dois found it to be 0.34 second; but when the frequency is exceedingly 

 great it declines to 0.199 second. 



Landois was able to ascertain the interesting fact that when the left ventricle 

 is enormously hypertrophied and dilated, the duration of the ventricular contrac- 

 tion does not materially exceed the normal. 



That the ventricle contracts more slowly when the action of the heart is 

 weakened is shown when the registering instrument is placed on the ventricle of 

 an animal that has been killed, and the heart-beat is recorded. In Fig. 30, from 

 the ventricle of a rabbit the slow heart-beats (B) are at the same time of longer 

 duration. 



This affords an opportunity to determine accurately the length of the period 

 to be allowed for the ventricular systole. Landois thought it wise, in order to 

 avoid misunderstanding, to distinguish the following three separate factors: 



1. The interval between the two heart-sounds, that is, from the beginning of 

 the first to the end of the second sound (Fig. 2 8 , b e) . 



2. The time occupied by the blood in entering the aorta: This evidently ter- 

 minates at the depression between c and d (Fig. 28, E) ; its beginning, however, 



