

THE MECHANISM OF THE HEART PUMP 951 



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 com- 

 mencement of systole. 



In many cases the disease which occasions 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 consequence 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 hyper- 

 trophied, 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. Hiirthle'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. A strong current is passing 

 through this contact, as well as 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. 



TIME RELATIONS 



The time relations of the various events of the cardiac cycle are indicated 

 in the accompanying diagram (Fig 414). In man the heart beats on the 

 average about seventy-two times in the minute, so that each cardiac cycle 



