The stethoscope is used to perform auscultation during clinical examinations. Its apparent simplicity of design and use is largely offset by the wealth of physiological information it provides, concerning our state of cardiovascular, pulmonary or abdominal health.

The stethoscope is a medical instrument that allows you to perform auscultations, that is to say, listening to the internal sounds of the body. It is therefore an acoustic instrument that works by amplifying interior noises by resonance.

Composition

The traditional stethoscope consists of a pavilion covered with a membrane, on the back of which we can find a second bell, bell-shaped. The horn is connected to a flexible rubber tubing which splits and is threaded on a metal frame in Y, the lyre. This is adjustable in spacing, and carries at its ends the ear tips, removable and interchangeable.

Very sophisticated and efficient (and expensive) electronic stethoscopes exist but their use is reserved for specialists for specific examinations.

Operation

The sounds of the body are naturally muffled by the presence of organs, viscera, fatty tissue, bodily fluids, and they are “mixed” with each other in a hubbub that makes them clearly inaudible.

The stethoscope, applied to the skin at the level of the organ whose sounds you want to listen to (the heart, lungs, etc.), will be able to select the sounds emitted by this organ and amplify them. The sounds “hit” the pinna and the triggered acoustic wave propagates along the tubing and the lyre to the ear tips. It is the difference in size between the horn and the tips which explains the amplification of the sound by a phenomenon of resonance.

The term stethoscope comes from the Greek stethos (chest) and scope (to observe). It is therefore used during clinical examinations to listen to the sounds of the heart or the lungs, but also to listen to those of the blood vessels or the intestines.

Cardiac auscultation

Auscultation of a “normal” heart makes it possible to hear two close sounds:

• the first sound (B1) corresponds to the closing of the mitral and tricuspid valves to allow the ejection of blood during the ventricular contraction (or systole);
• the second noise (B2) corresponds to the closing of the aortic and pulmonary valves to fill the heart during ventricular relaxation (or diastole).

Heart abnormalities can be detected concerning the frequency, intensity or existence of additional noises:

• a double heartbeat, due to poor synchronization between the right heart and the left heart;
• deafening of noises, in case of heart failure, emphysema or pericardial effusion;
• increased heartbeat, a sign of mitral stenosis or high blood pressure;
• extra beats, galloping, for tachycardia;
• a “click”, during mitral valve prolapse or mitral stenosis;
• a heart murmur related to turbulent blood flow, caused by a malfunction of the mitral valve, aortic stenosis causing blood to flow back to the heart, or communication between the ventricles or between the atria;
• pericardial friction due to inflammation of the pericardium, the membrane surrounding the heart.

Pulmonary auscultation

Auscultation of the lungs allows you to hear the air circulating in the lungs. When everything is normal, a symmetrical vesicular murmur is heard.

Abnormal sounds are often the result of pulmonary pathologies:

• the vesicular murmur is abolished in case of pleural effusion, or deafened in pulmonary emphysema;
• bronchial rales are a sign of inflammation of the bronchi, while crackles may be a sign of pulmonary edema or pneumonia;
• pleural friction is linked to inflammation of the pleura;
• pulmonary murmurs are due to an amplified transmission of the glottic murmur.

Auscultation of blood vessels

The stethoscope can take the arterial pulse, measure blood pressure when used in conjunction with the blood pressure monitor, or detect and identify certain heart murmurs.

Abdominal auscultation

The stethoscope allows you to listen to airborne noises from the intestines and thus detect an obstruction or paralysis of the digestive tract.

Other uses of the stethoscope

The stethoscope is also commonly used in fields other than medical:

• to research explosive devices firing systems;
• to locate a plumbing leak;
• to identify a strange noise in mechanics;
• to find the secret code of an armored door or a safe.

The stages of operation

Despite its apparent simplicity of operation, certain preambles are necessary to properly use your stethoscope and obtain the best possible sound transmission:

• the tips must face forward in order to be in good continuity with the ear canal;
• the lyre must have the correct spacing to avoid uncomfortable tension (by gently bringing or spreading the branches, it can be adjusted);
• in the case of a dual-head stethoscope, you have to open the one you are using and close the other (by rotating).

Which pavilion to use?

• The horn with membrane allows you to hear high frequency sounds (treble);
• The bell horn allows you to hear low frequency (bass) sounds.

Precautions to take

Some precautions should be taken to maintain a strong stethoscope:

• the right size ear tips, especially in the case of flexible tips, for a good seal and optimal sound transmission;
• clean horns, especially the bell horn, where debris can accumulate in the sensor and prevent the sound passage (some models offer removable membranes for protection);
• good airtightness: the parts of the pavilions must be checked, the tubing must not be cracked, the end fittings must be in good condition;
• storage away from excessive temperatures and harmful products;
• regular maintenance with 70% alcohol.

Depending on the intended use, there are different types of stethoscopes.

The different stethoscope models

• The monobloc chestpiece stethoscope, ideal for taking blood pressure;
• The dual-head, or dual-frequency diaphragm, stethoscope for listening to low-pitched and high-pitched sounds;
• The small head stethoscope, for infants and children, or very skinny people;
• Pinard’s obstetrical stethoscope (made of a wooden or aluminum cone) to listen to the fetal heart;
• The cardiological stethoscope, with high acoustic sensitivity, to detect cardiac disorders;
• The electronic stethoscope that isolates and amplifies sound up to 18 times more than a traditional stethoscope.

Before the stethoscope

In the past, doctors listened to bodily sounds by placing their ears directly on people’s chests, which was on the one hand tricky in the case of women, and on the other hand very unsatisfactory in the case of people of heavy build.

In 1816, Laennec had the idea of ​​rolling up sheets of paper to listen to the heart of a very stout patient: mediate auscultation was born and the very first stethoscope was soon made. Through trial and error and improvement, in 1961 Dr. Littmann created the dual-head stethoscope which is still in use today.