In not a few instances certain sounds may be found on listening to a chest with a stethoscope closely resembling crackles, rales or rubs, which really are not due to any pulmonary disease but to some other cause. The important causes of such sounds are as follows: Occasionally over the bases of the lungs, especially in the axillary regions, are heard friction-like sounds or crepitation, due, it is said, to the lung peeling away from the diaphragm. These are called marginal sounds because they are only heard at the edges or margins of the lungs. They are not associated with any evidence of disease. This phenomenon is so rare as to be negligible.
In thin, nervous young men, and less often, women, muscle sounds are sometimes so loud as to cause confusion. These sounds resemble a low-pitched rumble or roar. While only very rarely do these sounds resemble rales, not infrequently they are sufficiently in evidence to render it difficult to hear what other sounds (rales) or otherwise may be present. One type of these sounds can still be heard when the patient is not breathing and in this way may be easily distinguished from rales; another type is heard at the end of forced inspiration with muscular effort. Concentration during breathing on the part of the physician, and avoidance of too deep breathing by the patient, should prevent mistakes due to this cause.
¥. T. Lord has described a peculiar grating sound occasionally heard in the back which to a greater or less degree resembles a friction rub. This is due to a roughening of the surfaces of the subscapular bursa or to nodulated muscles. If this sound occurs on moving the shoulders up and down without breathing, any pulmonary lesion can be at once ruled out. This condition is too rare to be of much importance.
Ewart has called attention to ‘motor joint crackles’ as a frequent cause of wrong diagnosis. Perez originally described this phenomenon which bears his name. It is a well-known fact that auscultation over any of the larger joints will on movement reveal sounds which very closely resemble fine, dry rales; this is particularly true of the shoulder joint. Such crepitations can often be felt as well as heard. They are not so common in children. These crackles are often transmitted along the clavicles and can usually be distinctly heard over the upper part of the sternum, and in many cases over the apices, front and back. In a few instances, particularly among women who on breathing bring their shoulder muscles involuntarily into play, distinct rales are heard at one or both apices which are really motor joint crackles due to the slight movements of the acromio-humeral, and the sterno-clavicular joints. In any suspected case the patient should be instructed to go through the motion of breathing without taking any air into the lungs. If the sounds still continue they are not true rales but motor joint crackles.
In listening to the chests of stout women beyond middle age or in other persons who breathe superficially from habit or weakness, especially in old and bedridden patients, it is not unusual to hear an explosion of crackles after the first deep inspiration or cough. The explanation usually given to account for the rales thus obtained (for they are real rales) is that the air has been driven into certain far corners of the lungs by the forced breathing, to which it does not usually gain entrance and thereby opens up a certain number of closed alveoli causing the crackles or fine rales. These are usually heard over the bases of the lungs; they are not constant but disappear after one or two deep breaths. They are most often found in stout women who present no other signs or symptoms of tuberculosis, constitutional or local. These atelectatic rales ought never to be the cause of any mistakes in diagnosis.
Among the other sounds which may simulate rales are those caused by the hair against the diaphragm of the stethoscope if this form of instrument is used. These may be excluded by wetting the skin and stethoscope, or by the use of cold cream or vaseline.
Key Takeaways
- Marginal sounds are rare and not associated with disease.
- Muscle sounds can mimic pulmonary conditions but can be distinguished by patient breathing patterns.
- Motor joint crackles often occur in shoulder joints and should be ruled out before diagnosing lung issues.
Practical Tips
- Concentrate during auscultation to distinguish between muscle sounds and actual rales.
- Instruct patients to perform breathing motions without inhaling to identify motor joint crackles.
- Use cold cream or vaseline on the stethoscope to prevent hair interference with sound detection.
Warnings & Risks
- Do not mistake marginal sounds for signs of pulmonary disease as they are rare and benign.
- Avoid misdiagnosing muscle sounds as rales, which can lead to unnecessary treatment.
Modern Application
While this chapter focuses on historical diagnostic techniques, understanding these non-pulmonary causes of abnormal lung sounds remains crucial today. It helps in accurate triage and prevents over-diagnosis or under-diagnosis of respiratory conditions.
Frequently Asked Questions
Q: What are marginal sounds and why should they be disregarded?
Marginal sounds, heard at the edges of the lungs, are due to lung tissue peeling away from the diaphragm. They do not indicate any disease and are so rare that they can usually be ignored.
Q: How can one distinguish between muscle sounds and actual rales?
Muscle sounds often resemble a low-pitched rumble or roar and may continue even when the patient is not breathing. Concentration during auscultation and instructing the patient to avoid deep breaths can help in distinguishing them from true rales.
Q: What are motor joint crackles and how do they differ from pulmonary sounds?
Motor joint crackles occur due to movements of joints like the shoulder, which can transmit sounds resembling fine dry rales. These sounds continue even when the patient is not breathing and can be distinguished by moving the shoulders without respiration.