« AnteriorContinuar »
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, as we have already seen, of roughness or deposit on the inner surface of the vessel. It would appear, indeed, from the labours of Chauveau and Marey, that roughness of the internal surface of arteries does not anywhere, nor in any case, give rise to murmur. But the question is still open for discussion, whether the condition of the blood produces this modification. Agreeing with the opinion that arterial murmur is due to contraction of the artery at the point of murmur, and to the vibration incidental to a change in the arterial tension, I cannot but state that in many cases where I have met with intense murmur, there have been signs of anæmia; and that the murmur has borne a relationship in intensity with the more determinate indications of the anæmic condition. There are various methods of explaining this observation, the best of which is that of Marey; viz., that in anæmia there is a feebler arterial tension and less resistance to the current of blood in the capillaries. But whatever the explanation, it is certain that the relationships I have pointed out are true; and that anæmia, though not a cause of the murmur, has a qualifying influence upon it.
EXACT CHARACTER OF SUBCLAVIAN MURMUR. The murmur differs in character in different cases, and sonetimes in the same case. It may be a soft musical coo, so short and so slight as to be mixed with and obscured by the respiratory sounds. It may be a loud, coarse, almost snorting gush, conveying an unpleasant thrill to the ear, and, during its transit, obscuring the vesicular murmur of respiration. It may be loud, and yet so short, as to resemble a sound produced by a quick blow, with dull resonance. These are the three typical forms of the murmur, but between them there may be various distinctive shades. The musical cooing murmur, for example, may be intensified to a whistle, or a ringing noise; and the coarse murmur, to an absolute rasp. The murmur under one or other type is always best developed when it occurs in the right subclavian space, but it is most common on the left side.
DIAGNOSIS OF SUBCLAVIAN MURMUR, DIFFERENTIAL
AND ABSOLUTE. Differential Diagnosis. There are four physical signs of disease, diagnosable by the stethoscope, with which subclavian murmur may possibly be confounded, and especially by those who are not familiar with the details, as well as the principles, of physical diagnosis. These physical signs are
Aneurism of the aorta at the arch, or of the innominate artery, or of the subclavian itself, are the first diseases to be differentiated. I have said, that on four occasions I have known subclavian murmur set down as aneurismal; I may add to this, that in one of these cases the life of the patient was refused
for insurance on the suspicion of subclavian aneurism. The following diagnostic points are, however, always sufficient to establish the difference between subclavian murmur and any thoracic aneurism.
In aneurism the character of the bruit is usually the same at all times, the point of maximum intensity being one fixed spot, on which the mouth of the stethoscope may be placed, day by day, with the same effect. In subclavian murmur, the bruit may change in character several times during one examination; being at one time coarse and loud, at another gentle and musical. The point of maximum intensity may also differ by the variation of an inch laterally on either side.
In aneurism the murmur is permanent. In subclavian murmur the sound comes and goes. It will sometimes stop in an instant, and not reappear for many hours. In one case I knew it to be absent for three weeks, and then suddenly to recur and remain for a period equally long; again to subside, and again to present itself; and so on during many months of observation.
In aneurism, the murmur is not influenced by the movements of respiration. In subclavian murmur, the sound can be intensified by a moderately full inspiration ; can often be stopped by a forced inspiration; and, again, can be equally stopped by a prolonged expiration.
In aneurism, the stethoscope produces no change in the murmur, however firmly the pressure may be applied ; except in extreme cases, where the tumour