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this are demonstrative. The murmur is synchronous with the systole of the heart, and with the radial pulse. It is also limited to the traject of the subclavian artery. Traced downwards towards the heart, it is lost; traced in any other direction over the chest-surface, it is lost. Moreover, it is often limited to a certain point in the course of the artery, the space most common to it being a horizontal line about an inch long beneath the middle of the clavicle, or verging a little towards the outer end of the bone. A respiratory sound would, of course, have no such limitation. It happens truly, in many examples, that some modification of respiratory movement occurs antecedently to the murmur. Thus, I have met with many instances in which the murmur was present at no other time than during a deep and sustained inspiration; whilst in other examples, where it has been present during an ordinary inspiration, it has been destroyed by deep and sustained inspiration; but as, in numerous cases, it also happens that, by changing the position of the arm, the murmur may be intensified, or lessened, or destroyed, independently of the respiration, it follows that the murmur is not respiratory. The character of the sound, again, is different both from a respiratory sound and a friction sound; it is essentially a pulsatile bruit, in which respect it approaches very nearly to an aneurismal
The view of the arterial origin of subclavian murmur is further corroborated by examples where the thrill of the vessel can be felt by the finger at each pulsation. In one instance, where this thrill was intense, I could see the vibration when the finger was removed; and not only so, but on applying the ear near to the artery, without actual contact with the skin, I could hear the murmur.
Lastly, it is not difficult, in applying the stethoscope over the subclavian, to catch the murmur by a light pressure, and to remove it by a firm pressure, of the mouth of the tube. In such cases, the stethoscope, by arresting the current of blood through the artery when the pressure is made considerable, removes the sound by stopping the circulation. Under such pressure, the radial pulse is also felt to be deficient or absent.
The cause of the vibration of the artery is nevertheless primarily external; that is to say, the sound is in the artery, but is not due to disease of the vessel. I imagined at one time that in some cases, where the murmur was very intense, there might be deposit on the inner surface of the artery; but this idea was soon dispelled by the observation, that in every case the murmur could be removed by some simple change in the position of the arms of the patient, or in the force of respiration.
The view advanced by Dr. Kirkes as to the cause of the murmur was to the effect that the artery, at the moment when the sound was produced, was subjected to pressure upwards and forwards by a portion of solidified lung raised during inspiration. This explanation, which is the one also given by Dr. Sibson, in so far as it assigns to external pressure upon the artery the first step towards the production of the murmur, must be taken, I assume, as correct; it is a
I view to which I was led very early in my inquiries, and it accords with the facts. At the same time, it must not be conceived that the external pressure brought to bear upon the artery to produce the murmur is invariably exerted by the lung; such a view would not accord with all the facts.
There are, I believe, two modes by which the pressure on the artery may be exerted, when the subclavian murmur is present.
Firstly, there is a class of cases in which the pressure is produced by diseased lung. In these examples, there is, I believe, mostly, some solidification at the apex of the lung on the side on which the murmur is heard ; the solidification may be due to deposit of tubercular matter, or to enlarged and indurated bronchial tubes. In such instances, the character of .
, the murmur varies according to the condition of the lung-substance. If there is a diffused tubercular matter, with general dulness on percussion and deficient respiration, the murmur is only to be elicited at the acme of a deep inspiration. It is then heard very softly, as a gentle fleeting coo, irregular in its occurrence, and often not distinguishable without difficulty from a reflected heart-sound.
In other cases, where tubercular deposit is laid down in one spot immediately in contact with the artery, and where the deposit is hard, or when there is enlargement and induration of bronchial tubes immediately behind the artery, the murmur, which will still only be heard during inspiration, is sharp and shrill, or shrill and grating. It will continue so long as the breath is being held, and will disappear immediately on expiration. The murmur thus caused is often well marked in the early stages of phthisis, but disappears in later stages, when the deposit of tubercle has undergone the changes of softening and removal.
In another class of cases, where chronic bronchial disease is at a distance from the subclavian region, the pressure seems to be made on the artery by healthy lung acting under undue distension for compensation. In these examples, the murmur is very soft and fleeting, occurring only at the acme of inspiration.
Secondly, the murmur may be presented without any disease in the structure of the lungs. It will be seen, indeed, on reference to the table already given, that out of the fifty-one cases I observed, there were no fewer than nineteen in which pulmonic disease was absent; added to which, I have seen many examples of the murmur in persons in perfect health. In all these examples, the pressure exerted on the artery is, in my opinion, brought about by the action of the subclavius muscle, and is the result of those occupations in which the arms are being constantly thrown forwards and downwards, as occurs in wood-planing, hand-sawing, French polishing, and the like.
As I indicated in describing the first case in this essay, position of the arm makes a decided modification
in the sound; that is to say, when the arm is parallel with the body, the murmur is at its minimum, or is absent: when the arm is at a right angle with the body, or a little above the right angle, the murmur is at its acme. This is explained by the fact, that in the first named position the subclavius is relaxed; in the last the subclavius is exerting its contraction to help to steady the shoulder; thus the artery, pressed down by the muscle, is borne towards the margin of the first rib, and the murmur is elicited. This explanation of a modification of murmur by position of the limb bears on the influence of occupation. For, when the arm is thrown forwards, as in planing, and is brought back again by a brisk effort, the subclavius at each movement is brought into active play, the artery is pressed so as to impinge on the rib, and, as this proceeding is repeated for many years, the parts so adapt themselves that the position of the vessel is modified by the circumstances, and subclavian murmur becomes a permanent, but of itself a harmless phenomenon.
The two methods by which the sound is educed are then analogous in their action, but they are very different in their meaning in a prognostic sense. They may be singly at work; or, as will be readily seen, they may be working in combination, as when a man in whom the murmur is present as a mere mechanical effect of muscular contraction, becomes the subject of tubercular deposit or bronchial disease.
These modes of production are sufficient to account for the existence of subclavian murmur, independently,