THE MECHANISM OF THE HEAET PUMP 949 



In the experiment from which this figure was taken, the heart sounds were recorded 

 at the same time as the apex beat. It will be seen that the first heart sound, correspond- 

 ing to the ventricular systole, begins, not at the commencement of the rise of the cardio- 

 gram but at the notch near the top of the ascent. The first part of the ascent is therefore 

 caused by the increase in the volume of the ventricle, due to the sudden contraction of 

 the auricles, the ventricular systole being marked by the notch near the top of the 

 curve. Owing to the co-operation of the volume and pressure factors in the production 

 of the cardiogram, the curve generally begins to decline with the diminution in volume 

 which follows the sudden opening of the aortic valves. Here again however, the effect 

 will vary with the pressure of the button. If an actual deformation of the ventricular 

 muscle can be effected, as in thin patients, the plateau of the curve may last during the 

 whole of the cardiac cycle. Other forms of curves may be obtained which show 

 considerable deviation from the endocardiac pressure tracing ; these are spoken of as 

 atypical, and are generally conditioned by a faulty position of the cardiograph, the 

 button being applied to the chest wall in the immediate vicinity of the apex beat 

 instead of to the apex beat itself. 



P'IG. 413. Cardiogram (B) with simultaneous record of heart sounds (A). 



(HtJETHLE.) 



1, position of first heart sound; 2, position of second heart sound. 



THE HEART SOUNDS 



If we apply our ear to the front of a person's chest (it is more convenient 

 to use the stethoscope for the purpose), we hear two distinct sounds accom- 

 panying each beat of the heart, followed by a pause corresponding to the 

 diastole. The sounds are compared to the syllables lubb, dup, the first 

 sound being low-pitched and prolonged, the second sound high and sharp. 

 Thus the heart sounds may be represented : lubb, dup (pause), lubb, dup 

 (pause). 



The causation of the second sound is very simple and may be considered 

 t. It is heard just over the second right costal cartilage, i. e. the place 

 here the aorta lies nearest the surface. It comes at the end of the systole, 

 as determined by the hardening of the apex of the heart, felt as the apex 

 at, and can be shown to be synchronous with the closure of the aortic 

 alves. It is in fact caused by the sudden shutting and stretching of 

 hese valves, that occur directly the heart ceases to contract and to force 

 he blood into the aorta. If the valves be hooked back in an animal by 

 cans of a wire passed down a carotid artery, the second sound disappears 

 nd is replaced by a murmur caused by the blood rushing back' into the 

 entricle at the end of the systole. The same disappearance of the normal 



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