THE MECHANISM OF THE HEART PUMP 907 



In the normal individual sounds produced in this way are so slight that 

 they may be neglected ; under abnormal conditions, as after diseases 

 affecting the valvular orifices of the heart, this vibration may occur during 

 every heart cycle and be heard with ease on applying the ear to the chest. 

 These murmurs, or bruits as they are called, are of paramount importance in 

 enabling the medical man to form a judgment as to the condition of the 

 different valves of the heart. Thus injury to an aortic valve, so as to allow 

 of leakage during diastole, involves the squirting of a small amount of fluid 

 under high pressure from the aorta into the relaxed ventricle. On listening 

 to the chest of a man with such a lesion this regurgitation during diastole is 

 heard as a rushing sound occurring in the place of or continuing the second 

 sound up to the beginning of the next first sound which denotes the beginning 

 of systole. 



In many cases the disease which occasioned the inadequacy of the valve 

 is followed by processes of repair and cicatrisation in which the valves become 

 puckered and contracted and perhaps adherent, so that the orifices can never 

 become thoroughly patent or thoroughly closed. Under such circumstances 

 vibrations will be set up in the current of blood as it escapes through the 

 narrow orifice into the aorta during systole, and on listening to the chest 

 over the second right costal cartilage a ' to and fro ' bruit is heard composed 

 of a systolic immediately followed by a diastolic murmur. | In the same way 

 incompetency of the mitral valve or dilatation of the mitral orifice, in con- 

 sequence of weakness of the cardiac muscle, gives rise to a murmur which 

 lasts during the whole of the ventricular contraction and is therefore systolic 

 in character. Such a murmur is heard best over the apex beat, and is also 

 transmitted backwards so that it can be heard on listening at the back of 

 the patient. A narrowing of the mitral orifice in consequence of contraction 

 of the valves will set up a resistance to the flow of blood from left auricle to 

 left ventricle. The auricle becomes hypertrophied, its contraction prolonged, 

 and the escape of blood through the contracted orifices gives rise to a murmur 

 which is heard on listening over the apex beat as a presystolic bruit. This 

 bruit is easily distinguished from a systolic murmur by noticing that it runs 

 up to and ends with the apex beat, whereas a systolic murmur does not 

 begin until the elevation of the apex commences. 



Several physiologists have succeeded in recording heart sounds graphically. Hurthle's 

 method consists in an application of the microphone. A special form of stethoscope is 

 so arranged that by its means the vibrations corresponding to the heart sounds are 

 transmitted to a contact between silver and carbon. Through this contact a strong 

 current is passing. This also passes through an electro-magnet, which attracts an iron 

 disc attached to the membrane of a Marey's tambour. Any vibration transmitted to 

 the carbon-silver contact alters its resistance, and so the strength of the current passing 

 through the electro-magnet. In this way the heart sounds can affect the pull exerted 

 by the electro-magnet on the membrane of the tambour, and the change in the volume 

 of the contained air is recorded by means of an ordinary registering tambour. 



Similar results have been obtained by Einthoven, who has allowed the variations 

 in the current passing through the microphone to be recorded directly by means of a 

 very delicate capillary or string electrometer. 



