34 



Physiology. — "On thi' limrt-rlujllnu." III. Bj- Dr. S. de Boer.. 

 (Comimmioated by Prof. J. K. A. Wertheim Saeomonson). 

 (Gommunicateil in the meeting of April 23, 1915.) 



<)n till' riiiiijionents of the n-v-intcrval. 



In tlie estiinatioii of tlie disturbances of tlie I'liytlimic fiiiietioiis of 

 the heart the a-w-interval plays a comparatively important part. It 

 is consequently of great interest to know exactly by what factors 

 the duration of this interval is determined. Wiien determining this 

 interval, we measure the time that elapses between the beginning 

 of the auricle-systole and the beginning of the ne.\t following systole 

 of the ventricle. What we determine in this way is consequently 

 not only the time of transmission of the stimulus from the place of 

 entrance into the auricle till the time of entrance into the ventricle; 

 for it is obvious that, in our determination, we have not left out of 

 account the time that tlie stimulus has required to e.xert influence 

 upon the ventricle, i.e. the time of the latent stimulation. If now we 

 make our estimation by means of mechanical curves, then the latter 

 amount is rather imjiortant, but with electrograms this latent time 

 exists likewise. 



It is now my intention to represent this with some curves. 



In Fig. I we see two rows of curves of a suspended frog's heart; 

 the rhytiim of auricle and ventricle is halved. A stimulator is applied 

 to the basis ventriculi by which we administer at the end of the 

 diastole an extra-stimulus (tlie closing strokes at which the signal 

 goes down are prevented, the opening strokes — motion of the signal 

 upwards — reach the ventricle'. The first stimulus of the upper row 

 of curves falls in the refractory period. The second opening stroke, 

 which takes place later in the heart-period occasions an extra-systole 

 with a rather long latent period. After this extra-systole follows the 

 auricle-systole of the normal rhythm, the «-y-interval between this 

 auricle-systole, and tiie then following systole of the ventricle is almost 

 twice as long as the ^?-r-interval of the normal rhythm. It is obvious, 

 that the cause thereof is to be found in the decreased irritability of 

 the ventricle-musculature by the shortening of the preceding pause, the 

 stimulus coming from the auricle requires more time to exert influence 

 upon the ventricle. 



In the second row of this figure we see a repetition of this 

 phenomenon with the same result for a stimulus occurring a little 

 earlier. We see here, at the same time, that the latent time after 

 an extra-stimulus is the longer in proportion as the stimulus takes 

 place earlier in the heart-period. This figure illustrates likewise 



