Their character, as caught by the ear, is always more or less blowing, the passage of fluid in this respect offering very close analogies to that of air through a constricted aperture. We are not sufficiently familiar with the laws of its production to be able to deduce from an analysis of the character of the sound the exact changes in which it originates, but in general terms it may be assumed that when the murmur is very soft the solid parts are not very greatly altered, and that when very rough, grating, or musical, there is either very considerable constriction, or a semi detached mass floating down the current, and thrown into vibra tion as the blood passes. It is a point of some difficulty to deter mine when roughness and prolongation ought to be set down as only a modification of normal sound—when they ought to be regarded as something additional or superadded taking its place; the booming first sound of hypertrophy, and the reduplicated second sound of unequal contraction, ought never to be called bruit The readiest mode of determining whether the murmur be systolic or diastolic is to place the finger where the heart can be felt striking on the chest. If the sound oommence at a period equally distant from each of two impulses, and intermediate be tween them, the sound is diastolic, it ends just before the heart strikes on the chest. g on the contrary, it be nearly coincident with the stroke, it is systolic--it commences about the same time as the impulse, and ends long before the next stroke is felt When the murmur is systolic, the sound produced by the moving of the blood may be either due to alterations in the orifices through which it passes, or to changes in the character of the blood itself, or to a combination of both. But if a bruit be recognized to be diastolie„ it may be decided at once that there is valvular imper fection; and in the majority of instances there is disease of t,he aortic valves, by which blood is allowed to return into the left ventricle.
If we inquire into the mechanism of the circulation, we find that the force with which the blood passes from the auricle into the ventricle is much feebler than that by which it is propelled into the arteries, and also that the power of the left ventricle is very much greater than that of the right ; and, inas much aa the circulation through the arteriea is carried on during the interval between one systole and the next by the resiliency or contractile force of the vesaels, the rebound in the aorta and in the pulmonic artery, in cases of im perfect valves, are each in proportion to the muscular power of their respect ive ventricles. In addition to this, we have the pathological fact that disease of the aortic valves is • common occurrence, while disease of the pulmonic valves is very rare. During the systole, the ventricles empty themselves of blood with a force equal to the contractile power of each muscular wall ; and the vibration ofjhe particles of blood thus produced, when its relative pro portions deviate—from those of health, become audible, even when there is no unusual obstruction to the current, During the diastole, again, the ventricles are filled; and when there is no- alteration of texture in the cardiac aper tures, no change of quality in the blood is ever sufficient to develop audible vibrations, since the movement is caused only by the feeble contractions of the auricles. When the auriculo-ventricular aperture is very much altered by disease, especIally ff the vibratory power of the blood be at the same time increased by anemia, a diastolic bruit is sometimes produced on the left side of the heart ; on the right aide it has never been recognized. When, again, the aortic valves close Imperfectly during the diastole, the ventricle is partly filled from this source also ; and the force with which the resiliency of the arter7 drivea it back against the roughened or imperfect valves, and still more the circumstances of its meeting with the current from the mitral valve in an opposite direction, is quite sufficient to produce audible vibration. The very
same circumstance might happen on the right side of the heart, but I am not aware that it has evereen recorded ; and the amsBer amount of contractile force in the mammary artery. as well as the rarity of disease of the pulmonie valves, would lead us to expect that the event should be • very rare one.
A. Diastolic Murmurs.—When a diastolic murmur is mimi. nixed, we have really, in practice, only to determine whether it be aortic or mitral.
a. The probabilities are much in favor of the former, consider. in the relative frequency of each.
b. Mitral diastolic murmur, as it presupposes very considerable change in texture in the valve, cannot, one would imagine, exist without a mitral murmur also accompanying the systole : this is not necessarily the case in patency of the aortio valves.
c. The position at which each is heard in its greatest intensity, and the direction in which it is prolonged, are distinct, though not differing so greatly as to form such a ready means of diagnosis as might be d priori expected.
d. Further evidence of insufficiency of the aortic valves, if this be presumed to be the cause of murmur, is to be obtained from the character of the pulse, which seems to be left almost empty by the blood falling back upon the heart after each stroke, and again filling the artery with a jerk.
The aortic diastolic is, in fact, a murmur of regurgitation, while the mitral is not ; and this would of itself, apart from the consideration of force, explain the different frequency of each : for it is not necessary that there be any roughness or constriction of the aortic valves ; a smooth aperture left by tear ing or ulceration of a valve which permits regurgitation, when the recoil of the blood follows the systole, of necessity causes a diastolic murmur by en countering the opposing current of the blood. Hence, a systolic bruit at the aortic valves is not always to be heard when a diastolic one is present, as I believe is unavoidable at the mitral orifice. With this, too, is closely con nected the fact that the position at which the sound is heard in its greatest intensity is not so different as might be supposed. In some cases, no doubt, the blood is set into vibration, as it passes the roughened or constricted valves in its backward course ; but in other instances the vibration only begins when it meets the current from the auricle : in the one case it can be traced for several inches in a slanting direction, from the root of the aorta towards the apex, of pretty nearly equal intensity throughout; in the other, while the direction remains the same, the length may be diminished to about an inch near the centre of the heart. The mitral diastolic murmur Jima.. to about the same point, and will be readily understood how difficult it must be to determine a difference in direction, although nearly at right angles to each other, when the whole extent in each case does not exceed an inch. There is, however, one point characteristic of the mitrel diastolic murmur; the vibra tion is produced at the valve itself, and the sound is always heard in greatest intensity there, and diminishes in distinctness as it passes across towards the sternum to meet the line of the aortic diastolic murmur; such a circumstance, without the hammering pulse, would be to my mind sufficient for the diagnosis. On the other hand, a hammering pulse would very probably decide in favor of insufficiency of the aortic valves, even when the loudest sound seemed to be nearest to the apex.