Daring the existence of pericarditis, many circumstances occur to conceal the ordinary sounds of the heart: and when there is any difficulty in distin guishing them in the praicordial space, they should be listened for above the base of the heart, in the second intercostal space.
There are two circumstances which chiefly tend to render friction-sound liable to be confounded with other bruits : viz., a scanty secretion of lymph, and an abundant secretion of serum. The friction may in either case be single; in the former it is almost always limited to the reflexion of the peri cardial membrane at the origin of the great vessels, and might therefore be taken for an aortic murmur; but in addition to the indications derived from the other characters enumerated, it is especially to be noted that its position and point of greatest distinctness are below, and not above the base ; the very opposite is true of an aortic systolic murmur, and an aortic diastolic murmur presents other features which are very distinctive. If friction be obscured by the presence of serum, the point where it is most likely to be met with is the apex ; here, too, in position it is much below the ordinary situation of a mitral murmur; but it is further to be recognized by the circumstance that it is much louder when the ribs are depressed at the end of expiration, and may be very often rendered temporarily so by simple pressure.
Friction differs from endocardial murmur in its acoustic properties very decidedly, when a well-marked example is compared with the pure bellows sound ; and the student ought to make his ear familiar with their respective characters ; but in many cases he must be prepared to find each approximate so closely to the other that the character of the sound is not sufficient to de note whether it be formed in the heart or pericardium.
The best mode of determining whether the rhythm of a double bruit heard in the priecordial space differ from or coincide with that of the systole and diastole, is to listen above the base of the heart, where pericardial friction always becomes inaudible ; when the ear is fully accustomed to the rhythm of 1st and 9d sounds as there heard, the stethoscope should be immediately to the point at which the bruit is most distinct; if it be will at once detect the difference in duration, and the want of harmony with that just listened to.
The discovery of friction may be taken as unmistakable evi donee of the presence of pericarditis, and hence the importance of being able clearly to determine its true character. In speak ing of pericarditis (Chap. X.XII. § 1), the ordinary correlative symptoms will be pointed out ; and while, on the one hand, these may be no striking as to leave no doubt in the mind of the ob.
server that changes in percussion resonance, or in the rhythm and intensity of the heart's action, are due to pericarditis when friction cannot be detected, yet on the other they may have been so slight that but for the presence of friction we should not know of the existence of the inflammation at all. The change of fric tion into creaking is far less common in the pericardium than is the pleura ; when such a sound is heard, the principles of its diag nosis are the same as those already given for a single friction bruit, and it will be all the easier because of its creaking charac ter, which is so unlike an endocardial murmur. There is only one further question in regard to friction which the observer has to determine, in order that his diagnosis of pericarditis may be qikite certain ; it is that the friction is really in the pericardium, and not in the adjacent pleura. Now, the only chance of its being in the pleura is, when it is local—to one side, and not in front of the heart ; and if the doubt be suggested to the mind, its validity can readily be tested by making the patient hold his breath ; but it must be remembered that pericardial friction be comes more distinct, or may be only audible when are depressed, and therefore the patient should be taught to hold his breath after an expiration, not after an inspiration.
§ 8. Endocardial Murmurs.—Either sound of the heart may be prolonged beyond its ordinary duration, and lose its usual dis tinctness, when the sound is commonly called rough : or they may be entirely superseded by a lengthened bruit, which has either a character of extreme softness (the true bellows-murmur, or bruit de souffle), or that of a very harsh grating noise, or even ap proaches to a musical tone. From the slightest degree of rough ness or prolongation, to the loudest possible bruit, every link is filled up by murmurs which glide by insensible gradations into each other, and unite the extremes together under one common denomination. The essential element in their production is an altered relation of the blood to the solid structures, whether by change in the one or in the other ; and they are only beard when the blood is in motion. They therefore correspond exactly to the systole or diastole of the ventricle as the blood is passing out of, or into those cavities : they may commence a little before or a little after the true time of the natural sound ; they may be carried on through the interval of pause, but they cease directly when the opposite action comes into play, either to be followed by the natural sound to which that gives rise in health, or by a bruit corresponding in time to it.