A reader suggested that I write about the stethoscope. At first, I wondered if such an article would have much interest to a general audience; but then I realized that there was a lot to say about this instrument that might have wide appeal.

The stethoscope was invented by one of the epochal figures of early 19 century medicine – René-Théophile-Hyacinthe Laennec (1786-1821). Laennec’s other contributions to medicine were descriptions of peritonitis and cirrhosis. The latter is often referred to as Laennec’s cirrhosis. He also described melanoma and its propensity to metastasize. He did his melanoma work as a medical student.

If a physician wanted to listen to sound emanating from the chest he had to place his ear against the patient’s thorax. Many physicians were uncomfortable doing so with female patients. Laennec’s first stethoscope was a wooden and brass monaural device in three parts. A stethoscope doesn’t amplify sound, rather it focuses it. Its use and our understanding of the information it provides hasn’t changed much over the past two centuries.

One of Laennec’s first stethoscopes

Using his primitive device Laennec was able to describe rales, rhonchi, crepitance, and egophony. He presented his findings and research on the stethoscope to the Academy of Sciences in Paris, and in 1819 he published his masterpiece, De l’auscultation médiate ou Traité du Diagnostic des Maladies des Poumon et du Coeur. Laennec became so adept at auscultation that by comparing what he heard with what was observed at autopsy that he was able to make accurate diagnoses that had eluded the profession prior to his invention. The modern binaural stethoscope with two earpieces was invented in 1851 by Arthur Leared.

Most modern stethoscopes have a bell and a diaphragm which can be rotated to allow use of either. The bell transmits lower frequency sounds while the diaphragm transmits higher frequencies. In practice, I mainly used the diaphragm.

The stethoscope is so identified with the medical profession that it is now more totem than tool. As most physicians were never very good using it to full effect it is now mostly a fashion statement. The current style is to drape it over your neck. When I came of age in the medical profession it was customary to keep the scope in a side pocket. I never foreswore this placement.

A reason that most physicians aren’t very good at auscultation is that modern imaging techniques have made them lazy. When properly used by a doctor who is fluent with the stethoscope a lot of useful information can be gained at little extra cost. Obviously, the doctor who finds himself in a remote location may have to rely on his diagnostic skills as there will likely be no sophisticated imaging device readily available.

Typically, the stethoscope is used to listen to the chest, but it also is useful in examining other parts of the body. Both normal and abnormal bowel sounds can be heard with a stethoscope. The gurgling intermittent sounds are part of normal function. High pitched sounds may be an early sign of bowel obstruction. A silent abdomen indicates ileus – lack of intestinal activity.

Bruits are vascular sounds resembling heart murmurs. Sometimes they’re described as blowing sounds. The most frequent cause of abdominal bruits is occlusive arterial disease in the aortoiliac vessels. If bruits are present; they’re typically heard over the aorta, renal arteries, iliac arteries, and femoral arteries. A bruit heard in the neck over the carotid arteries indicates narrowing of the artery.

But as mentioned above, it’s listening to the chest that gives the most useful clinical information. The careful examiner using palpation, percussion, and auscultation can detect many pulmonary and cardiac abnormalities. I’ll leave the first two of these for another time and concentrate on the use of the stethoscope.

Inspiratory wheezes are a feature of asthma. In severe cases wheezing can be heard by just standing near the patient. Expiratory wheezes usually indicate disease in the upper airway, such as bronchiolitis. Many other disorders too long for a general article can cause wheezing.

Rhonchi are continuous low pitched, rattling lung sounds that often resemble snoring. Obstruction or secretions in larger airways are frequent causes of rhonchi.

Rales are an abnormal rattling sound. They can be caused by pneumonia, heart failure, or massive fluid overload. Apical rales are diagnostic of tuberculosis, the disease the killed both Laennec and his mother, and which he was able to accurately diagnose with his instrument. Crepitant rales resemble the sound produced by compressing and rubbing hair between your thumb and middle finger next to your ear. Egophony is an increased resonance of voice sounds heard when auscultating the lungs, often caused by lung consolidation and fibrosis.

The most interesting use of the stethoscope is in listening to the heart. The video below gives an excellent summary of both normal and abnormal heart sounds.

Careful auscultation of the second heart sound (S2) can yield very useful clinical information. The figure below shows normal and three abnormal forms of splitting of this sound. The second sound normally is more widely split during inspiration due to delayed closure of the pulmonic valve secondary to increased return of blood to the right side of the heart caused by the increase in negative intrathoracic pressure. It is important that the patient breathe normally and not hold his breath while listening to heart sounds. The video below the figure goes into detail with aural examples of how to diagnosis changes in this sound . Briefly, fixed splitting indicates some sort of right ventricular dysfunction, while paradoxical splitting is associated with left ventricular dysfunction.


Pericarditis of any etiology may be associated with a pericardial friction rub. This sound is an audible medical sign used in the diagnosis of pericarditis. Upon auscultation, this sign is an extra heart sound of to-and-fro character, typically with three components, one systolic and two diastolic. It resembles the sound of squeaky leather and often is described as grating, scratching, or rasping and may seem louder than or may even mask the other heart sounds. The sound usually is best heard between the apex and sternum but may be widespread. The clinician must remember that while hearing this rub makes the diagnosis of pericarditis, though not its cause, pericarditis may present without a rub. The brief video below presents the sound and the causes of pericarditis.

I’ve just sketched the utility of Dr Laennec’s 200 year old invention. Most physicians never were very good with it. Unfortunately, the number of those expert with it is in steady decline. The widespread availability of useful video tutorials makes ignorance of how to use this emblematic device inexcusable for anyone who’s not a surgeon. But the most important practice in getting the most from a stethoscope is practice – a lot of it.

The photo above the title is the stethoscope I used for most of my medical career. It was with me during every patient encounter.