172 



CIRCULATION OF THE BLOOD 



5. THE APEX BEAT 



We have in the apex beat a means of studying the different questions which 

 have to do with the pressure relations and the form changes of the heart 

 in the normal animal and in man. By placing the hand on the chest wall, 

 where the heart is not covered by the lungs i. e., in the fourth or fifth inter- 

 costal space an impulse can be felt with 

 every ventricular systole, which is called the 

 apex beat. In lean individuals an elevation 

 of the intercostal wall can be observed with 

 the eye. This fact is of itself sufficient to 

 show that the heart actually strikes against 

 the chest wall, but does not on the other hand 

 prove that the ventricle withdraws from it 

 in diastole. In diastole the heart is flabby 

 and weak. If one presses with the finger on 

 the exposed heart at this time, only a little 

 resistance is felt, even though the finger 

 does not make a permanent impression. 



As soon however as the ventricular sys- 

 tole begins, the heart suddenly becomes hard 

 and exerts a very strong pressure on the 

 finger. Everywhere it feels as if the finger 

 were being pressed against. This sudden 

 hardening is the essential cause of the apex 

 beat (Harvey, Kiwisch, Marey). In addi- 

 tion to this however there is an effort on 

 the part of the ventricle to assume such a 

 form that the apex will stand vertical to the 



base (Carlile, Ludwig). Consequently the heart in its systole takes the posi- 

 tion with reference to the chest wall described by the dotted line in Fig. 59. 

 The apex, therefore, strikes against the thoracic wall and pushes it forward 

 to a slight extent. 



In opposition to this, Shreiber remarks that the heart chambers must assume 

 the same form (a right cone) after the auricular contraction and before the 

 beginning* of the systole. But this follows of necessity only in case the ven- 

 tricles become turgid with blood a thing which rarely results from auricular 

 contraction. With an ordinary filling of the ventricles their diastolic form may 

 be very different, just as an india-rubber balloon may vary in shape until it is 

 highly inflated, when it becomes spherical. 



Other factors also have been brought forward for theoretical explanation of 

 the apex beat. It has been assumed, for example, that the heart beat against 

 the thoracic wall is due chiefly to the rebound consequent upon the ejection of 

 blood from the ventricle, or in other words, has its origin in the stretching and 

 elongation of the great arteries by means of which the heart is thrown forward. 

 It is possible that these factors do in fact contribute to a certain extent in pro- 

 ducing the beat. But that they are not the only factors, and do not even repre- 

 sent the most important mechanism concerned, appears from such facts as these : 

 first, the forward movement can be observed on an excised heart empty of blood 



FIG. 59. Schema illustrating Lud- 

 wig's theory of the apex beat. 

 The dotted line represents the 

 position of the heart in systole. 



