Stethoscope

The stethoscope (Greek στηθοσκόπιο, of στήθος, stéthos - chest and σκοπή, skopé - examination) 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 (breath sounds), though it is also used to listen to intestines and blood flow in arteries and veins.

History

The stethoscope was invented in France in 1816 by René-Théophile-Hyacinthe Laënnec. It consisted of a wooden tube and was monaural. In 1851 Arthur Leared invented the binaural stethoscope which has become the standard ever since. By 1873, there were descriptions of a differential stethoscope that could connect to slightly different locations to create a slight stereo effect, though this did not become a standard tool in clinical practise.

Several other minor refinements were made to stethoscopes until in the early 1960's Dr. Littmann, a Harvard Medical School professor, created a new stethoscope with vastly improved acoustical performance.

Dr. David Littmann was a distinguished cardiologist and international authority on electrocardiography. In 1961 he described his "ideal" stethoscope in the November issue of the Journal of the American Medical Association. The device included an "open chestpiece for the appreciation of low-pitched sounds, a closed chestpiece with a stiff plastic diaphragm to filter out low-pitched sounds, firm tubing with a single lumen bore, the shortest practical overall length, a spring with precise tension to hold the ear tubes apart, and light and convenient to carry and use." The Littmann Stethoscope was referred to as a "two-sided chestpiece" stethoscope and was originally made by a small, Cambridge Massachusetts company, Cardiosonics. There were two models, the doctor's stethoscope and the nurse's stethoscope. Dr. Littmann 's description of his invention is what is now referred to as a "combination " or "two-sided chestpiece " stethoscope... a major advancement in stethoscope technology at the time.

The Littmann Stethoscope rapidly became the stethoscope of choice in America and its original design is still the basis for most stethoscopes used in medical practice today.

Current practice

The stethoscope is used in aid of diagnosing certain diseases and conditions. 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 in hopes of hearing something.

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.

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 stethoscope 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 require conversion of acoustic sound waves to electrical signals which can then be amplified and processed for optimal listening. Unlike acoustic stethoscopes, which are all based on the same physics, transducers in electronic stethoscopes vary widely. The simplest and least effective method of sound detection is achieved by placing a microphone in the chestpiece. This method suffers from ambient noise interference and has fallen out of favor. Another method, used in Welch-Allyn's Meditron stethoscope, comprises placement of a piezoelectric crystal at the head of a metal shaft, the bottom of the shaft making contact with a diaphragm. 3M also uses a piezo-electric crystal placed within foam behind a thick rubber-like diaphragm. Thinklabs uses a stethoscope diaphragm with an electrically-conductive inner surface to form a capacitive sensor. This diaphragm responds to sound waves identically to a conventional acoustic stethoscope, with changes in an electric field replacing changes in air pressure. This preserves the sound of an acoustic stethoscope with the benefits of amplification.

Methods of examination

Trivia

The root of the word stethoscope is the Greek word stethos which mean "chest".

External links

BBC: Smart stethoscope for detecting kidney stones

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