THE MECHANISM OF THE HEART PUMP 905 



varies from case to case and may be altered by altering the degree of pressure 

 put on the recording button. In the first figure given the auricular systole 

 finishes before the main rise of the lever occurs. In many cases, however, 

 the elevation due to the auricular systole may take up the greater part of the 

 ascending limb of the curve, as in Fig. 403. 



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 



1 2 



FIG. 403. Cardiogram (B) with simultaneous record of heart-sounds (A). 



(HlJRTHLE.) 



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



first heart sound, corresponding to the ventricular systole, begins, not at 

 the commencement of the rise of the cardiogram, 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 con- 

 siderable 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. 



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 

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

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



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