1020 PHYSIOLOGY 



tion of the volume and pressure factors in the production of the cardio- 

 gram, 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 



1 2 



FIG. 402. Cardiogram (B) with simultaneous record of heart-sounds (A). 



(HURTHLE.) 



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



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. 



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 dis- 

 tinct sounds accompanying 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. a It comes at the 

 end of the systole, as determined by the hardening of the apex of the 

 heart, felt as the apex beat, and can be shown to be synchronous 

 with the closure of the aortic valves. It is, in fact, caused by the sudden 

 shutting and stretching of these valves that occur directly the heart 

 ceases to contract and to force the blood into the aorta. If the valves 

 be hooked back in an animal by means of a wire passed down a carotid 

 artery, the second sound disappears and is replaced by a murmur 

 caused by the blood rushing back into the ventricle at the end of the 



