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giving 3 cases; and, lastly, a single case of bronchial affection combined with tubercular deposit. These relationships will have to be further considered in the sequel.
Finally, the table shows a curious circumstance in reference to occupation. It will be seen that, in the vast majority of the cases, the patients were employed in manual labours, in the exercise of which the arms are thrown forwards and downwards. Thus there are no fewer than fifteen cabinet-makers in the list; men who are engaged all their lives in planing, sawing, and polishing. There are four carpenters, two sawyers; and so on. When I first observed this connection of the murmur with certain mechanical arts, I began to inquire into the matter carefully. I thought it might be that the men of these trades were more fully represented in the list of patients than others. This turned out to be a fallacy; for, of the 2000, there were many more tailors than cabinetworkers, and more clerks than tailors, and more sempstresses than clerks. I began consequently to inquire how far the special occupation influenced the result. To get at the truth in this direction, I collected eight cabinet-makers who were quite well, and to my surprise found that they all presented the murmur. I extended the observation to carpenters also, and found the same thing, though not so frequently. Blending, therefore, these facts with those which tell us how rare the murmur is in women, and that it is absent in children, I am driven to the inference that particular mechanical actions of the arms
long continued, have an influence in producing the peculiar sound; how and why, we shall see better in a succeeding page.
CAUSE AND CAUSATION OF SUBCLAVIAN MURMUR.
The whole tenor of my observations leads me to the conviction that subclavian murmur is of arterial origin. In this view I shall be supported by the majority of auscultators, but shall be at variance with at least one, I mean Dr. Thorburn, who, speaking of the sound, remarks: “It must either be a respiratory sound modified by the heart and great blood-vessels, so as to have a cardiac rhythm ; or a vascular sound modified by respiration. From a careful examination, I have come to the conclusion that it is of the former character: and that what is heard is the expiratory murmur and the end of the inspiratory murmur itself, saccadée or jerked by some undue impulse. I think it probable that this impulse is communicated by a nervously excited or perhaps slightly dilated aorta, just as the action of the heart may sometimes give a cardiac rhythm to a friction-sound which is really pleural. The greater comparative weakness of expiration will account for its being heard chiefly at that time.”
I have said that Dr. Thorburn is alone in his opinion; but his hypothesis is ingenious, and well put. It is necessary, therefore, in disposing of it, to use careful and logical argument in favour of the opposite view ; viz., that subclavian murmur is an arterial sound, modified by respiration. The proofs of 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 murmur.
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 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