184 ACOUSTIC PHENOMENA WITHIN THE VEINS. 



In all cases in which there is no external pressure, it is found that the pro- 

 duction of spontaneous acoustic phenomena is greatly facilitated if, during the 

 period of arterial diastole, the arterial wall is as relaxed as possible and, therefore, 

 becomes suddenly and greatly distended at the time of the pulse-wave, that is, 

 when the systolic minimum of tension of the arterial wall is rapidly displaced by 

 the diastolic maxirmim of tension. This is particularly the case with aortic in- 

 sufficiency, a condition in which the arteries are often the seat of widespread 

 murmurs. If even during arterial rest the minimum of tension of the arterial 

 wall is relatively high, the acoustic phenomena are faint and may even disappear 

 altogether. 



The following factors favor the development of arterial murmurs: (i) A suffi- 

 cient degree of delicacy and elasticity of the vessel-walls; (2) a low peripheral 

 resistance, that is, accelerated and unobstructed escape of the blood from the end 

 of the vascular channel; (3) a material difference between the pressure ot the fluid 

 in the stenotic portion and that of the fluid in the peripheral dilatation; (4) large 

 size of the artery. 



Murmurs may be heard also in normal pulsating arteries, especially when 

 the vessel is the seat of sharp bends or tortuosities. In almost all cases in which 

 arterial murmurs are heard, one or several of the foregoing factors can be demon- 

 strated. It is evident that murmurs of this kind will be most marked when two 

 or three large arteries are found in close apposition. Hence the rather loud 

 murmur generated in the many tortuous and dilated arterial trunks of the gravid 

 uterus (uterine or placental souffle) and the much less distinct funic souffle in the 

 two umbilical arteries. In this category belongs also the so-called cerebral murmur 

 heard in almost one-half of all infants with thin skulls, as well as the murmur 

 heard over the morbidly enlarged spleen, and the thrill in the thyroid gland in 

 cases of exophthalmic goiter. 



When auscultation is practised over the ulnar artery under the favorable 

 conditions mentioned, especially in lean individuals, every pulse-beat is found to 

 be accompanied by two acoustic phenomena, which coincide with the primary 

 and the dicrotic elevation. In old persons especially, and in individuals with a 

 bigeminate pulse, the two sounds are quite distinct. Friedreich believes the first 

 sound to be produced by the vessel-wall, that is, the sudden tension of the artery 

 distended during diastole. The second murmur naturally is feebler, in correspond- 

 ence with the lesser degree of distention of the artery by the dicrotic elevation. 

 Occasionally a third sound is heard between the other two, which corresponds to 

 the elasticity-oscillations between the apex of the curve and the dicrotic elevation. 

 In the radial artery and in the dorsalis pedis only a single murmur is, as a rule, 

 heard synchronously with the pulse-beat. 



In cases of aortic insufficiency characteristic acoustic phenomena are present 

 in the femoral artery. When the vessel is compressed, there is heard a double 

 blowing (murmur) , the first element of which is due to the fact that a large mass 

 of blood is driven to the periphery synchronously with the pulse, and the second 

 to the fact that during the contraction of the artery a large quantity of blood 

 flows back into the ventricle. On the other hand, if the artery is not compressed, 

 two feebler sounds are heard, which are due to the fact that the auricle and the ven- 

 tricle send a wave of blood into the arterial system in rapid succession (Fig. 55, III) . 

 Gerhardt similarly heard, in cases of insufficiency of the pulmonary valves, two 

 dull sounds over every portion of the pulmonary surface. In other cases (when 

 there is also tricuspid insufficiency) the second sound is produced by the sudden 

 snapping closure of the valves in the femoral veins, caused by the rebound of 

 the venous blood. Also, when the arteries are rigid (atheroma) a double sound 

 is sometimes heard synchronously with the pulse- wave. This sound is attributed 

 to the anacrotism of the pulse observed under such conditions. 



ACOUSTIC PHENOMENA WITHIN THE VEINS. 



The Venous Hum. Above the clavicle, in the fossa between the origin of the 

 two heads of the sternocleidomastoid muscle, most commonly on the right side, 

 there is heard in many individuals (40 per cent.) a sound that may be continuous, 

 or synchronous with the diastole of the heart, or even with inspiration, and of a 

 roaring or buzzing, sometimes hissing or singing, character. This sound is generated 

 within the bulb of the common jugular vein and is called a venous hum. If 

 present even when no pressure is exerted with the stethoscope, it is a pathological 

 symptom. The phenomenon may be heard in almost any subject if pressure be 



