The stethoscope (Gk. stethos - chest & skopeein - to examine) is an acoustic medical device for auscultation, i.e. listening to internal sounds in the human body. It is most often used to listen to heart sounds and breathing, though it is also used to listen to intestines and to blood flow in arteries and veins.

History

The stethoscope was invented in France in 1816 by René-Théophile-Hyacinthe Laennec. It consisted of a hollow wooden tube. Legend has it that Laennec invented the stethoscope so that he would nto have to place his ear against the breasts of French women. It is unclear whether Laennec was attempting to avoid his own, or his patients' embarrassment. Nevertheless, one might say that "mother was the necessity of the invention".

Current practice

There are currently two types of stethoscopes - acoustic and electronic.

Acoustic stethoscopes are familiar to most people, and operate on the transmission of sound from the chestpiece, via air-filled hollow tubes, to the listener's ears. The chestpiece usually consists of two sides that can be placed against the patient for sensing sound - a diaphragm (plastic disc) or bell (hollow cup). If the diaphragm is placed on the patient, body sounds vibrate the diaphragm, creating acoustic pressure waves which travel up the tubing to the listener's ears. If the bell is placed on the patient, the vibrations of the skin directly produce acoustic pressure waves traveling up to the listener's ears. The bell transmits low frequency sounds, while the diaphragm transmits higher frequency sounds. This 2-sided stethoscope was invented by Rappaport and Sprague in the early part of the 20th century. The problem with acoustic stethoscopes is that the sound level is extremely low, making diagnosis difficult.

Electronic stethoscopes overcome the low sound levels by amplifiying body sounds. Currently, a number of companies offer electronic stethoscopes, and it can be expected that within a few years, the electronic stethoscope will have eclipsed acoustic devices.

Electronic stethoscopes operate on a number of principles. In most cases, a microphone is placed within a bell or behind a diaphragm, and the microphone converts the sound in the chestpiece to an electronic signal for amplification. This is the method used by companies such as 3M Littmann and Cardionics. The most recent innovation, by Thinklabs, is the direct detection of body sounds using a custom stethoscope sensor. Thinklabs technique uses an electrically-conductive diaphragm to directly convert diaphragm vibrations into electronic signals. In a Thinklabs stethoscope, since the diaphragm is in contact with the body, the conversion of sound to electronics is direct, rather than using a microphone placed inside a chestpiece separated from the body by air in the chestpiece.

The stethoscope is used in aid of diagnosing certain diseases. The stethoscope is able to transmit certain sounds and exclude others. Before the stethoscope was invented, doctors placed their ear next to the patient's body.

Stethoscopes are often considered as a symbol of the doctor's profession, as doctors are often seen or depicted with a stethoscope hanging around their neck.

Stethoscopes are also used by mechanics to isolate sounds of a particular moving engine part for diagnosis.

See also:

• Physical examination
• Inspection (medicine)
• Palpation
• Percussion

• Fetal stethoscope

External link

• Thinklabs Electronic Stethoscope
• BBC:Smart stethoscope for detecting kidney stones