October 14, 1897] 



NATURE 



567 



THE MECHANISM OF THE FIRST SOUND 

 OF THE HEART. 



WHILST every one knows that the action of the heart 

 is accompanied by. sounds described as the first 

 and second sounds of the heart, it is a remarkable fact 

 that the mechanism by which the former of these pheno- 

 mena is produced remains undetermined. It may be 

 said to be almost universally accepted that the second 

 sound is the result of the sudden tension of the semi- 

 lunar valves, caused by the resistance which they offer to 

 reflux of blood from the great vessels into the ventricles 

 on the cessation of the systole. The difficulties which 

 exist are connected with the first sound, and they result 

 mainly from the fact that a number of events occur 

 simultaneously with the systole of the ventricles and with 

 the sound. Two of the most striking of these events, 

 namely, the closure of the auriculo-ventricular valves and 

 the muscular contraction of the walls, are regarded by 

 many authorities as the source of the first sound. Sir 

 Richard Quain in a paper recently read before the Royal 

 Society has given a very graphic account of certain im 

 portant investigations which lead him to the conclusion 

 that neither of these explanations is correct, and which 

 at the same time enable him to indicate what he believes 

 to be the real explanation of the first sound of the heart. 



In the first place, the author of this communication 

 brings forward strong evidence to show that the action of 

 the auriculo-ventricular valves is not the source of the 

 first sound of the heart. This action consists in the 

 simple apposition of the lamina of these valves and the 

 closure of the orifices by the musculi papillares and 

 chordie tendineie, and affords no such tensive force as 

 would suffice to produce the loud and characteristic 

 sound which accompanies systole. More positive evi- 

 dence is derived from the fact that the first sound can be 

 heard independently of the existence and action of mitral 

 and tricuspid valves in some of the lower animals, 

 especially reptiles such as the python, which the author 

 carefully auscultated in the Zoological Gardens, or when 

 the valves are rudimentary, as in the kangaroo. The 

 mitral murmurs familiar to physicians are, of course, 

 formed at the mitral valve during systole ; but they have 

 no relation except in time with the first sound ; they are 

 merely accidental complications which occur at the 

 moment of ventricular contraction, and the healthy first 

 sound may be heard along with and independently of 

 them. 



In the second place. Sir Richard Quain shows that the 

 muscular contraction of the walls of the heart during 

 systole is not the source of the first sound of the heart. 

 It is true that muscular contraction is accompanied by a 

 sound, but this possesses neither the loudness nor the 

 characteristic tone of the first cardiac sound. In opposi- 

 tion to the old experiments of Ludwig and Dogiel, which 

 appear to show that after cutting off altogether the supply 

 of blood from the cavities, one can still hear a systolic 

 sound, the author puts the experimenls of Prof Holford, 

 who made out that the sounds are heard or cease, re- 

 spectively, according as blood is or is not admitted 

 into the chambers. The classical observation of Stokes 

 of Dublin that the first sound of the heart gradually 

 disappears in the course of typhus fever, does not prove 

 that muscular contraction causes the first sound, but that 

 the impulse of the heart is so feeble that it is unable to 

 produce the sound at the semilunar valves. The correct- 

 ness of this view is confirmed by the fact recorded by 

 Stokes, that the last point where the sound disappears in 

 typhus is over these valves, whilst it is at the same point 

 that it first returns. Further, Dr. Alexander Morison, 

 working for Sir Richard Quain, found that in the blood- 

 less heart of a recently killed turtle no sound could be 

 heard during contraction sufficient to expel blood from the 

 cavity. These facts and observations are, in the author's 



NO. 1459. VOL. 56] 



opinion, sufficient to prove that the contractile action of 

 the muscles of the heart are not capable of producing the 

 first sound. 



After this destructive criticism. Sir Richard Quain 

 proceeds to consider a third event which occurs during 

 systole, namely, the propulsion of the blood contained in 

 the ventricles into the pulmonary artery and aorta ; and 

 herein he finds the agency by which the sound in 

 question is produced. He maintains that the first sound 

 of the heart is caused by the impact of the blood driven 

 by the action of the muscular walls of the ventricles 

 against the block produced by the columns of blood 



; in the. pulmonary artery and aorta, which press upon 

 the semilunar valves. Dr. Pettigrew has shown that the 

 column of blood projected from the heart into the aorta 

 (to take the left side only as illustration), is formed by 

 the union of three columns with a spiral motion which is 

 the result of the spiral arrangement of the musculi 

 papillares and of the fibres of the walls of the ventricles, 



; as well as of the spiral shape of the left ventricular 

 cavity itself. By this rifle motion the blood is directed 



I against the segments of the semilunar valves, which are 

 hastily thrown apart, the spiral current being continued 

 for some distance within the aorta. This beautiful rifle 

 mechanism is constructed to give precision to the direction 

 of the moving body against a given point, and to secure 

 also velocity and force. In fact, we have here in nature 

 the mechanism of the modern rifle. A resistance to 

 the stream of blood from the ventricle is offered by 

 the block formed by the column of blood resting on 

 the aortic valves, wedged, and as it were screwed 

 tightly, into each other. Whatever may be the 

 absolute value of the propelling force of the left ventricle, 

 authorities are agreed that the driving power and the re- 

 sistance are to each other in the proportion of about four 

 to three, the really important point being the relation they 

 bear to each other. Now in this motion and in this re- 

 sistance we have all the elements for the production of 

 sound, inasmuch as sound is a phenomenon resulting 

 from resisted motion. A sound being produced, we ask. 

 What is it ? and the reply must be : The first sound of 

 the heart, the cause of which we seek. This explanation 

 was first suggested to Sir Richard Quain's mind many 

 years ago by a case of disease, in which the aortic valves 

 were completely broken down and had become inade- 

 quate to their function. A murmur of such intensity was 

 produced that it was audible three inches from the walls 

 of the chest without a stethoscope. Over the femoral 

 artery, however, there was no murmur, but a sound pre- 

 cisely resembling the first sound, caused by the motion 

 of blood in the artery which received the full force of the 

 ventricular contraction, the valves being destroyed. His 

 attention was thereby directed to the natural obstruction 

 offered by the aortic valves in health to the blood leaving 

 the ventricle. Many observations have been made on 

 the circulation in the femoral artery under like circum- 

 stances by continental physicians, but these have had 

 reference to diagnosis only, not to the cause of the first 

 sound of the heart in health. 



An objection might be offered to this explanation of the 

 first sound of the heart, that it is heard more distinctly at 

 the apex of the organ, a point removed from the seat of 

 the valves. The observation is correct, and the explana- 

 tion of it is simple. The muscular walls of the heart are 

 connected with the fibroid ring intimately associated with 

 the semi -lunar valves. The sound produced at these 

 valves is communicated to the apex of the heart through 

 the fibroid ring and the muscular walls, which at the 

 moment of systole are tense and firm. The sound thus 

 conducted reaches that portion of the heart which is un- 

 covered, and which is in contact with the walls of the 

 chest. But, on the other hand, when opportunity offers, 

 it has been found that the sound in question is heard 

 over the aortic valves more distinctly than in any other 



