THE APEX BEAT 175 



of rising tension (period of closure) of the ventricle. This period is not by any 

 means always clearly delimited, and could have but small practical value. 



In order to determine the moment of closure of the semilunar valves on the 

 human cardiogram, the heart sounds have been auscultated and marked on the 

 curve by means of an electric signal. The exactness of this method is not great 

 however, and from observations of this kind one can say with certainty only that 

 the second heart sound falls somewhere in the course of the descending limb of 

 the cardiogram. Attempts have been made therefore to determine this moment 

 by other methods. 



In man Hiirthle and Einthoven have registered the heart sounds automat- 

 ically in various ways and have found that the second sound comes about 0.02 

 second after the beginning of the steep descent. 



Finally, Edgren has attempted to solve the problem by simultaneous regis- 

 tration of the apex beat and the pulse. Since the pulse wave requires a certain 

 time to propagate itself from the root of the aorta to the place where the pulse 

 is taken, this time must be subtracted. It is then found that the elevation on 

 our cardiogram designated f corresponds to a similar mound on the intracardial 

 pressure curve (Fig. 58, v') an d corresponds exactly with the well-known dicrotic 

 elevation of the pulse curve. This, as we shall see later, is intimately connected 



FIG. 62. Curves of the apex beat (lower line) and of the carotid pulse (upper line) of man, 

 simultaneously recorded, after Edgren. 6, 6, and /, /, are corresponding points. 



with the closure of the semilunar valves. On this ground it appears justifiable 

 to assert that the mound is produced by the stretching of the semilunar valve. 



In so doing we do not wish to assert that the valves are closed then for the 

 first: for that this event transpires much earlier is proved by a comparison 

 of the pressure curves of the ventricle and of the aorta (Fig. 58). It is not 

 improbable that a short time after the noiseless closure of the valves, they are 

 suddenly put on the stretch by the aortic blood acting under great pressure, 

 and that they produce in this way the second sound of the heart. This much 

 is certain, that the second sound cannot begin before the closure of the semi- 

 lunar valves (shortly after the beginning of the descending limb of the cardio- 

 gram) and not later than the mound f. 



On a typical cardiogram we can make, therefore, a definite determination 

 of the following points : auricular systole, beginning of the ventricular systole ; 

 b, opening of the semilunar valves, beginning of relaxation; f,, stretching of 

 semilunar valves. 



