

THE APEX BEAT 



173 



as well as on one with ligated arteries ; and secondly, the movement appears 

 immediately at the beginning of the ventricular systole, while the opening of 

 the semilunar valves and the ejection of blood into the great arteries follows 

 appreciably later (cf. page 171). 



The apex beat offers the only possibility of studying the heart movements 

 on a living man, and for this reason much attention has been devoted to its 

 graphic record, called the cardiogram. 



On animals the intracardial curve and the cardiogram can of course be 

 recorded simultaneously, the latter by pushing in between the chest wall and 

 the heart a small balloon which communicates with the writing tambour. In 

 the two curves, as shown in Fig. 60, we observe various similarities and dif- 



FIG. 60. Curves of pressure in the right auricle O, in the right ventricle V, and of the apex 

 beat P (horse), after Chauveau and Marey. 



ferences. In both we have at A the elevation caused by the auricular contrac- 

 tion ; likewise the steep rise at the beginning of the systole. On the cardiogram 

 this reaches its maximum earlier than does the ascending limb of the pressure 

 curve (B). After the maximum is once reached the pressure curve runs almost 

 parallel with the abscissa, or it rises gradually, then sinks suddenly at the end 

 of the ventricular systole. The cardiogram begins to fall much earlier, but does 

 so more gradually although finally it shows also a steep fall. 



At the line C we find almost at the base of the descending limb of both 

 curves a small elevation, which we shall presently discuss further. After the 

 end of systole the ventricle is filled with blood, and the pressure rises slowly up 

 to the succeeding systole. At the same time the cardiogram rises slowly above 

 the abscissa. If the contraction of an empty heart be recorded it has quite 

 another form from that of the cardiogram. From which it is evident that the 

 latter is not a simple contraction curve, but must be regarded as in fact a com- 

 bined pressure and volume curve of the heart chambers. It is a pressure curve, 

 for the reason that the button placed over the breast wall exerts a pressure 

 against which the heart does work. It is however at the same time a volume 

 curve, in so far as it is influenced by the volume changes of the heart. 



