SOUNDS AND MURMURS IN THE ARTERIES. 183 



As the smaller venous branches unite to form larger ones, the lumen 

 gradually diminishes toward the venae cavae : hence the velocity of the 

 current must increase in the same proportion. The velocity in the 

 venae cavae may be half as great as that in the aorta. 



Borelli estimated the capacity of the venous system as four times as large as 

 that of the arteries. According to A. v. Haller the proportion is as 9 14. 



As the pulmonary veins are narrower than the pulmonary arteries, 

 the blood moves more rapidly through the former than through the latter. 



SOUNDS AND MURMURS IN THE ARTERIES. 



The acoustic phenomena observed in the arteries must, from a strictly physical 

 standpoint, be designated as murmurs. Nevertheless it is customary in medical 

 nomenclature, following the example of Skoda, to apply the term sound to those 

 acoustic phenomena that are of short duration and sharp definition, like the heart- 

 sounds; while those that are of longer duration and are not distinctly delimited 

 are designated murmurs in the narrower sense. In many cases a sharp distinction 

 between the two is, therefore, impossible. 



In the carotid, and more rarely in the subclavian, two distinct sounds are 

 heard in approximately four-fifths of all healthy individuals. These sounds cor- 

 respond in duration and pitch to the two sounds of the heart and must be inter- 

 preted as due to propagation of the sound from the heart by means of the blood 

 as far as the carotid, and they are, accordingly, designated transmitted heart- 

 sounds. Sometimes the second sound of the heart alone is heard, as the site of 

 its production is nearer the carotid. The second sound of the pulmonary artery, 

 which is in close contact with the aorta, may also be transmitted to the point 

 mentioned. 



Sounds and murmurs occur either spontaneously or only after the application 

 of external pressure, by means of which the lumen of the vessel is narrowed. 

 Accordingly a distinction is made between (i) spontaneous sounds and murmurs 

 and (2) pressure-sounds and pressure-murmurs. 



Arterial murmurs are developed most easily by exerting pressure on a circum- 

 scribed portion of a large artery, for example, the femoral. The pressure must be 

 so regulated that only a small portion of the lumen remains open for the passage 

 of the blood (stenotic murmurs}. As a result, a small stream of blood will pass 

 through the stenotic point with great rapidity and force, and enter the wider por- 

 tion of the artery beyond the site of compression. This so-called pressure-stream 

 throws the fluid-particles into active oscillatory and rotatory movement and 

 thus produces the murmur in the wider, peripheral portion of the vessel. Analo- 

 gous conditions prevail wherever there is a kink, a sharp bend or a tortuosity 

 in the course of the artery. The phenomenon is, therefore, as a rule a pressure- 

 murmur generated within the fluid. With regard to the question as to the origin 

 of these murmurs, Geigel takes the stand that they are due to static transverse 

 vibrations of the vessel-walls. Below the point of compression a thrill is felt 

 in the walls of the large arteries synchronously with the pressure-murmur. In 

 cases of aortic insufficiency, exophthalmic goiter, and circumscribed arteriosclerosis 

 this thrill is much more marked than in normal cases, and it is also appreciable 

 over smaller arteries. 



A murmur of like character is that at times heard over the subclavian artery 

 synchronously with the pulse and designated subclavian murmur. This is pro- 

 duced by adhesions of the two layers of the pleura at the apices of the lungs, 

 especially in association with tuberculosis and other diseases of the lungs, and in 

 consequence of which the subclavian artery, as a result of torsion and kinking, 

 undergoes local stenosis, which sometimes manifests itself by diminution or absence 

 of the pulse-wave in the radial artery (paradoxical pulse) . 



Pathological. It is evident that murmurs will develop in the human body 

 likewise: (a) When, owing to morbid conditions, the arterial tube is dilated at 

 some point where the blood-current is forcibly introduced from a normal portion 

 of the artery. Such dilatations (aneurysms) quite generally give rise to murmurs 

 (bruits) . (6) Pressure-murmurs will be generated whenever an organ exerts pres- 

 sure on an artery, as, for example, by the greatly enlarged uterus during preg- 

 nancy, and by a pathological tumor pressing upon a large artery. 



