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The Stethoscope

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Study the sounds

Study the sounds

The term 'Stethoscope' is derived from two words: 'Steth' meaning 'chest' and 'Scope' meaning 'to inspect'. Here I discuss the history, use, and inner functioning of the stethoscope.

The Musician's Medical Device

Rene Laënnec invented the stethoscope in 1816. He was a French Physician and musician. He integrated his music skills into medicine and invented the stethoscope. As a musician, he was trained in the skill of carving his own wooden flutes. Great was his interest in the arts that he once even quit medicine to focus solely on music. But after a while, he decided to come back to this noble profession. As it is said, "The comeback is always bigger than the setback." It is during his comeback that he developed this masterpiece. His musical skills and clinical expertise helped him design the most famous and essential medical discovery which is found in every doctor's office.

A monaural Stethoscope gifted by Rene Laennec to a French Surgeon

A monaural Stethoscope gifted by Rene Laennec to a French Surgeon

The Innovative Invention

Rene Laennec wrote the story about this celebrated discovery in his classic treatise titled 'De l'auscultation médiate'. He talks about his interaction with a young obese woman with a diseased heart, in whose case clinical examination methods such as direct palpation and percussion were not practical due to the extreme degree of fatness. He goes on to explain that the other method which is direct auscultation by placing the ears on the chest to listen to the heart sounds was not appropriate on a young female patient.

Laennec was left with a need to find out the reason for the patient's ailment and the lack of resources to do so. Yet he had the will to find out what it was that ailed the patient. As it is said, "Where there is a will, there is a way." He recollected his musical knowledge and pondered upon how one can listen to the scratch of a pin at one end of a piece of wood while placing one's ear on the other end. He then rolled a piece of paper in a cylindrical manner and applied one end of it to the patient's chest and the other end to his ear. As he listened, he was fascinated by how clear and distinct the sound was when compared to direct placement of the ears.

Laennec had then discovered that the then newly discovered stethoscope was superior to the previously used method of placing the ear over the chest, particularly if the patient was overweight. A stethoscope also avoided the embarrassment of placing one's ears over a woman's chest.

Laennec auscultating using a monaural stethoscope

Laennec auscultating using a monaural stethoscope

The Way Up

The first stethoscopes were monaural, meaning it can be used to listen to sounds with only one ear at a time. The shape of those stethoscopes was cylindrical and they were usually made of wood and brass.

As the years went by, the design of the stethoscopes was met with numerous modifications such as the addition of rubber tubing, and earpieces that can be fit into both the ears. Some stethoscopes also have volume control. Currently, there are even stethoscopes that have recording and Bluetooth access to help the listener study the sounds better.


Binaural Stethoscope

Binaural Stethoscope

Parts of a Stethoscope

The three main parts of a stethoscope are:

  1. The chest piece
  2. The rubber tubing
  3. The ear frame

1. The chest piece

The classic form is two-sided, consisting of a bell and a diaphragm. The two sides are connected by a drum. The drum is in turn attached to a stem.

Some forms of chest piece have tunable diaphragms and they do not have a bell. Whereas certain forms have a convertible diaphragm where the bell end of the stethoscope can be converted to a small diaphragm by adding a flat attachment. This is particularly useful while auscultating in children.

2. The rubber tubing

The chest piece is connected to the ear frame through a rubber tubing. The stem of the chest piece is connected to a rubber tubing which is connected to the aural frame.

3. The ear frame

The ear frame, also known as the aural ('aural' meaning 'ear') frame consists of the aural tube and the ear tips. A 'U' shaped spring connects the aural tubes and allows them to be flexible during usage and to spring back together while not in use.

Note: Refer the figure below for the parts of the stethoscope.

Note the 'U' shaped centre that contains the spring

Note the 'U' shaped centre that contains the spring

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How to wear a stethoscope?

Step 1:

Hold the stethoscope with the ear tips pointing away from you. The pores in the ear tips will not be visible at your end when you hold it this way.

Step 2:

Insert the ear tips into your ear canal(external auditory canal). When rightly placed, the ear tips will align perfectly with the direction of the ear canal. It is essential to hold the stethoscope as directed in 'step 1' to achieve its perfect fit into the ear canal. When it is held the right way, the ear tips will be directed forwards and downwards, same as the direction of the ear canal. This will ensure its proper fit once placed into the ear canal.

Hold the stethoscope with the ear tips pointing away from you

Hold the stethoscope with the ear tips pointing away from you

Hold the stethoscope with the ear tips pointing away from you

Place the ear tips into the ear canal

Place the ear tips into the ear canal

Place the ear tips into the ear canal

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Before you auscultate

The term 'auscultation' means listening to the body sounds using a stethoscope.

Before you auscultate,

1. Open the bell or the diaphragm: To do this, hold the stem using the thumb and index finger of one hand. Rotate the chest piece to 180° using the other hand. When completely rotated to 180°, a click sound will be audible. This can be a guide to denote that either the bell or the diaphragm is open.

2. Determine which side of the chest piece is open: Place the ear tips on the ear. Tap on the diaphragm of the chest piece. If the tap is audible through the ear tips, it means that the diaphragm is open, If it is not audible, then the bell is open.

3. Stethoscopes with a tunable diaphragm: The diaphragm of these stethoscopes is pressure-sensitive. The diaphragm acts as a bell or a diaphragm based on the pressure applied during auscultation.

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Ready To Listen

Open the side of the chest piece that you want to use and start to auscultate the area where you want to listen to the body sounds.

When the chest piece is placed on the area of auscultation, the sound waves at that area get concentrated over the chest piece. These sound waves are then transmitted through the rubber tubing to the ear tips, making it audible to the ears.

The bell is the smaller side of the chest piece that can be used to listen to low-frequency (low-pitched) sounds. It has to be held lightly against the skin during auscultation to allow proper amplification of the low-frequency sounds.

The diaphragm is the larger, flat side of the chest piece that is used to listen to high-frequency (high-pitched) sounds. The diaphragm filters out the high-pitched sounds and accentuates the low-pitched sounds. It should be held firmly against the skin for proper amplification of the sounds.

In case of a stethoscope with a tunable diaphragm, place the chest piece lightly over the chest to listen to low-frequency sounds as with a bell. Place it firmly over the chest to listen to high-frequency sounds as with a diaphragm.

Stethoscope with tunable diaphragm

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Pressure-sensitive tunable diaphragm

Pressure-sensitive tunable diaphragm

What can you hear?

The stethoscope is used to listen to sounds in various parts of the body including the chest. These include:

  • Heart sounds
  • Lung sounds
  • Bowel sounds
  • Arterial sounds

The bell of the stethoscope can be used to listen to low-frequency sounds such as:

  • Mid-diastolic murmur of mitral stenosis
  • S3, third heart sound in heart failure.

The diaphragm of the stethoscope can be used to listen to high-frequency sounds such as:

  • Bowel sounds
  • Lung sounds
  • S2, the second heart sound
  • Aortic and pulmonary ejection clicks
  • Misystolic click
  • Early diastolic murmur of aortic regurgitation
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Phonocardiogram

Phonocardiography is the method of graphical recording of the heart sounds.

Phonocardiograph is the device used for Phonocardiography.

Phonocardiogram is the graph that is obtained using Phonocardiography.

Phonocardiography helps study the normal and abnormal heart sounds better with graphical analysis.

Normal S3 and S4, third and fourth heart sounds can not be heard on auscultation. S3 can be heard during auscultation only in heart failure. These sounds can be better studied using a phonocardiogram.

Medical device manufacturers are developing stethoscopes with attached phonocardiograph that will enable clinicians to achieve a thorough analysis of the heart sounds during auscultation.


Stethoscope with Phonocardiograph

ViScope

ViScope

Phonocardiogram

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