What is a stethoscope?
A stethoscope is an instrument that is used to amplify sounds. This is possible due to the fact that the diaphragm of a stethoscope covers a larger surface than the human eardrum. The tube running from the stethoscope diaphragm to the eardrum is airtight, helping to transfer vibrations in the diaphragm directly to the user’s eardrum. In the medical world, doctors use a stethoscope as a diagnostic instrument for heart and lung conditions, amongst others. The word 'stethoscope' is derived from the Greek 'stèthos', which means (chest) cavity.
History of the stethoscope
The stethoscope has an interesting history. The main developments are summed up below in chronological order: The stethoscope was invented in 1816 by René Laennec. The Laennec stethoscope looked like a horn and was made of wood. Laennec’s single-tube model was superseded in 1851 by the double-tube stethoscope designed by Arthur Leared. A year later, in 1852, George Cammann perfected Leared’s design and prepared it for commercial production. In addition, Cammann wrote a long treatise on the stethoscope as a diagnostic instrument. In the 1940s, Sprague and Rappaport developed a new type of stethoscope. A feature of their new model was that one side of the stethoscope was used to listen to the lungs (the respiratory system) while the other was especially suited to listening to the heart (the cardiovascular system). This new stethoscope soon became the standard. The Sprague-Rappaport was later manufactured by Hewlett-Packard. Hewlett-Packard's medical division, Agilent Healthcare, was later taken over and the Sprague-Rapport fell into the hands of Philips. It was only in 2004 that Philips’ medical division, Philips Medical, stopped manufacturing the model. Various minor adjustments followed until the early 1960s, when a Harvard Medical School professor, Dr. David Littmann, introduced a new stethoscope that was not only lighter but also performed better acoustically. Later in the 1970s, 3M Littmann introduced an extra-hard plastic diaphragm. The diaphragm is flexible at the edges. By exerting pressure on the chest-piece, the part of the diaphragm that vibrates can be reduced. This enables high tones to be heard. When the pressure on the chest-piece is then decreased, the surface of the diaphragm that starts to vibrate increases. The low tones can then be heard. 3M Littmann later developed a tube with a double internal lumen. In this tube, two channels separated by a septum run from the chest-piece and end in a discrete left and right ear bracket.
Types of stethoscopes
The acoustic stethoscope
This is the best-known stethoscope type. It is the traditional stethoscope in which the sound is picked up by a diaphragm. The acoustic pressure waves are transferred to the listener’s eardrum through the chest-piece. The sound is amplified because the diaphragm has a larger surface than the human eardrum. Nowadays, there are single-tube and double-tube acoustic stethoscope models available. The double-tube stethoscopes have an internal double lumen.
The electronic stethoscope
The electronic stethoscope can amplify sounds. In an electronic stethoscope, the sound is picked up in different ways. The easiest and most straightforward way of doing this is by positioning a microphone in the chest-piece. With this method, however, there can be a lot of interference from ambient sounds. Another method is to convert the sound into an electrical signal using a Piezoelectric crystal that is in contact with the diaphragm.
Using your stethoscope
If you can hear little or nothing:First check the following:
- Insert the ear bracket properly in your ears: The ear bracket regulates the course of the auditory channel. The auditory channel runs in a forward direction. It is therefore very important that the stethoscope and the ear bracket/ earpieces are inserted pointing forward. Some people have a differently shaped auditory channel. The ear bracket can be adjusted if it does not feel comfortable or if you cannot hear clearly.
- Earpieces: It is important that the earpieces sit comfortably in your ears, which is particularly important when using so-called Soft-Sealing earpieces. This is because when these soft-sealing earpieces are too large for the user, they can block the ear because they can become compressed.
- Check for obstructions: When a stethoscope is carried in the (doctor’s) coat, dirt can often block the ear bracket. This can be prevented by routinely cleaning and maintaining the stethoscope.
- Check that your stethoscope is airtight: In order for a stethoscope to function properly, it is important that the system is airtight, from the diaphragm up to and including the earpieces. Loose parts in the chest-piece can be a sign that the system is no longer airtight. This can also occur, of course, when the tube or earpieces are broken or damaged.
- Is the chest-piece turned to the proper side? The chest-piece in most stethoscopes must be rotated around the tube in order to alternate between the diaphragm and the clock (or paediatric diaphragm). To do this, rotate the chest-piece until you hear a 'click'.
If you are using the stethoscope correctly and you still cannot hear clearly, it may mean that the stethoscope needs to be cleaned. For more information, see the user guide for your stethoscope.
Performing maintenance on your stethoscope
- You can disinfect your stethoscope by wiping it all over with a 70% isopropyl alcohol solution or soapy water
- For a thorough cleaning, the earpieces can be removed from the ear bracket. Depending on the model, you can do this by rotating or pulling out the earpieces (Snap On earpieces). If the earpieces are attached with screw thread, remove them by screwing them anti-clockwise.
- Do not expose a stethoscope to extreme heat or cold, solvents or oils. Never immerse the stethoscope in liquids or in the autoclave. To disinfect your stethoscope, wipe it with a 70% isopropyl alcohol solution.