Stethoscope FAQs
Stethoscope FAQs
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types of stethoscope : stethoscope history : stethoscope maintenance : heart sounds : how does a stethoscope work? : buy stethoscopes
acoustic stethoscope : electronic stethoscope : noise reduction stethoscope : recording stethoscopes : fetal stethoscope
Acoustic stethoscopes are familiar to most people, and operate on the transmission of sound from the chest piece, 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. One problem with acoustic stethoscopes was that the sound level is extremely low. This problem was surmounted in 1999 with the invention of the stratified continuous (inner) lumen, and the kinetic acoustic mechanism in 2002. Acoustic stethoscopes are the most commonly used. A recent independent review evaluated 12 common acoustic stethoscopes on the basis of loudness, clarity, and ergonomics. They did acoustic laboratory testing and recorded heart sounds on volunteers. The results are listed by brand and model. [5]
An electronic stethoscope (or stethophone) overcomes the low sound levels by electronically amplifying body sounds. However, amplification of stethoscope contact artifacts, and component cutoffs (frequency response thresholds of electronic stethoscope microphones, pre-amps, amps, and speakers) limit electronically amplified stethoscopes' overall utility by amplifying mid-range sounds, while simultaneously attenuating high- and low- frequency range 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' Rhythm 32 inventor, Clive Smith 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.
Because the sounds are transmitted electronically, an electronic stethoscope can be a wireless device, can be a recording device, and can provide noise reduction, signal enhancement, and both visual and audio output. Around 2001, Stethographics introduced PC-based software which enabled a phonocardiograph, graphic representation of cardiologic and pulmonologic sounds to be generated, and interpreted according to related algorithms. All of these features are helpful for purposes of telemedicine (remote diagnosis) and teaching.
More recently, ambient noise filtering has become available in some electronic stethoscopes, with 3M's Littmann 3000 and Thinklabs ds32a offering methods for eliminating ambient noise. In acoustic stethoscopes ambient noise filtering is available in TRIMLINE Puretone (DRG, R. Deslauriers) external noise reducing models.
Some electronic stethoscopes feature direct audio output that can be used with an external recording device, such as a laptop or MP3 recorder. The same connection can be used to listen to the previously-recorded auscultation through the stethoscope headphones, allowing for more detailed study for general research as well as evaluation and consultation regarding a particular patient's condition and telemedicine, or remote diagnosis.
A fetal stethoscope or fetoscope is an acoustic stethoscope shaped like a listening trumpet. It is placed against the abdomen of a pregnant woman to listen to the heart sounds of the fetus. The fetal stethoscope is also known as a Pinard's stethoscope or a pinard, after French obstetrician Adolphe Pinard (1844-1934).
The word 'stethoscope' is derived from the Greek words for 'I see', and 'the chest.' The first stethoscope was invented in 1819 by Rene Laennec. This invention enabled doctors to detect a heartbeat with greater confidence and helped Dr Eugene Bouchut to win a prize from the Academy of Sciences in Paris in 1846 for 'the best work on the signs of death and the means of preventing premature burials'.
After experimenting on dead and sedated animals, in combination with observations of dying people, Bouchut believed that if a heartbeat was absent for more than two minutes, a person could be considered dead. In the face of opposition, he extended the period to five minutes. Even with this concession, death determined by a lack of heartbeat was only slowly accepted.
Several of Bouchut's chief critics were fellow contestants for the prize. They advanced ideas like introducing leeches near the anus, applying specially-designed pincers to the nipples, or piercing the heart with a long needle with a flag at the end, which would wave if the heart were still beating.
Monaural stethoscopes (having only one earpiece), were used from 1819 and, by the 1850s, they were the mainstay of the physical examination. The monaural model did become increasingly obsolete by the 1860s with the invention of binaural stethoscope (having two earpieces) in 1852. However, they were still used by many doctors into the late 19th and early 20th centuries.
The flexible vinyl, rubber and plastic parts of stethoscopes should be kept away from solvents, including alcohol and soap. Solvents can have detrimental effects including accelerating the natural aging process by dissolving the plasticizers that keep these parts flexible and looking new.
In addition, when they are manufactured stethoscopes with two sided chestpieces are lubricated where the chestpiece rotates around the stem and need to be re-lubricated periodically, just like any other machine. If these moving parts are not lubricated they grind together and ruin the fine tolerances required for the proper acoustic performance of the stethoscope. Cleaning the stethoscope will also remove lubricants making periodic lubrication essential.
Be careful to use only products that have been tested to be safe and effective for cleaning stethoscopes and other medical instruments.
Modern stethoscopes consist of a shallow bell-shaped device with a clear stiff diaphragm, connected to the ear pieces by flexible tubing and a hollow metal headset. The chest piece is placed directly on the patient's skin. As the patient takes deep breaths or the heart beats, sounds are amplified through the diaphragm or bell. These amplified sounds travel through the hollow flexible tubing and headset, finally reaching the examiner's ears through the tight-fitting earpieces. At this point the examiner can describe and assess the sounds they heard and apply them to their diagnoses and treatment.
Modern stethoscopes consist of a shallow bell-shaped device with a clear stiff diaphragm, connected to the ear pieces by flexible tubing and a hollow metal headset. The chest piece is placed directly on the patient's skin. As the patient takes deep breaths or the heart beats, sounds are amplified through the diaphragm or bell. These amplified sounds travel through the hollow flexible tubing and headset, finally reaching the examiner's ears through the tight-fitting earpieces. At this point the examiner can describe and assess the sounds they heard and apply them to their diagnoses and treatment.
Modern stethoscopes consist of a shallow bell-shaped device with a clear stiff diaphragm, connected to the ear pieces by flexible tubing and a hollow metal headset. The chest piece is placed directly on the patient's skin. As the patient takes deep breaths or the heart beats, sounds are amplified through the diaphragm or bell. These amplified sounds travel through the hollow flexible tubing and headset, finally reaching the examiner's ears through the tight-fitting earpieces. At this point the examiner can describe and assess the sounds they heard and apply them to their diagnoses and treatment.
Modern stethoscopes consist of a shallow bell-shaped device with a clear stiff diaphragm, connected to the ear pieces by flexible tubing and a hollow metal headset. The chest piece is placed directly on the patient's skin. As the patient takes deep breaths or the heart beats, sounds are amplified through the diaphragm or bell. These amplified sounds travel through the hollow flexible tubing and headset, finally reaching the examiner's ears through the tight-fitting earpieces. At this point the examiner can describe and assess the sounds they heard and apply them to their diagnoses and treatment.
Purchase stethoscopes online at www.amamedicalproducts.com.au . The site’s comprehensive content provides information on medical equipment, textbooks and supplies, and enables purchases to be made via a secure online facility. The site is aimed at medical professionals and students, offering an easy and cost effective way of purchasing high quality medical supplies online.
Popular models and accesories availble for purchase online include:
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Welch Allyn Harvey Elite - Black |
Littmann Classic II - Purple |
Littmann Clardiology III - Burgundy |
Littmann ID tag - Black |
The Auscultation Assistant - "provides heart sounds, heart murmurs, and breath sounds in order to help medical students and others improve their physical diagnosis skills"
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