Stethoscope
Overview
 
The stethoscope is an acoustic medical
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

 device for auscultation
Auscultation
Auscultation is the term for listening to the internal sounds of the body, usually using a stethoscope...

, or listening to the internal sounds of an animal body. It is often used to listen to lung and heart sounds
Heart sounds
Heart sounds, or heartbeats, are the noises generated by the beating heart and the resultant flow of blood through it...

. It is also used to listen to intestines and blood flow in arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

 and vein
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...

s. In combination with a sphygmomanometer
Sphygmomanometer
A sphygmomanometer or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just...

, it is commonly used for measurements of blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

. Less commonly, "mechanic's stethoscopes" are used to listen to internal sounds made by machines, such as diagnosing a malfunctioning automobile engine by listening to the sounds of its internal parts.
Encyclopedia
The stethoscope is an acoustic medical
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

 device for auscultation
Auscultation
Auscultation is the term for listening to the internal sounds of the body, usually using a stethoscope...

, or listening to the internal sounds of an animal body. It is often used to listen to lung and heart sounds
Heart sounds
Heart sounds, or heartbeats, are the noises generated by the beating heart and the resultant flow of blood through it...

. It is also used to listen to intestines and blood flow in arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

 and vein
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...

s. In combination with a sphygmomanometer
Sphygmomanometer
A sphygmomanometer or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just...

, it is commonly used for measurements of blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

. Less commonly, "mechanic's stethoscopes" are used to listen to internal sounds made by machines, such as diagnosing a malfunctioning automobile engine by listening to the sounds of its internal parts. Stethoscopes can also be used to check scientific vacuum chambers for leaks, and for various other small-scale acoustic monitoring tasks. A stethoscope that intensifies auscultatory sounds is called phonendoscope.

History

The stethoscope was invented in France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 in 1816 by René Laennec
René Laennec
René-Théophile-Hyacinthe Laennec was a French physician. He invented the stethoscope in 1816, while working at the Hôpital Necker and pioneered its use in diagnosing various chest conditions....

 at the Necker-Enfants Malades Hospital
Necker-Enfants Malades Hospital
The Hôpital Necker – Enfants Malades is a French teaching hospital, located in Paris, France. It is an hospital of the Assistance publique - Hôpitaux de Paris group, and is affiliated to the University of Paris Descartes...

 in Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

. It consisted of a wooden tube and was monaural. His device was similar to the common ear trumpet
Ear trumpet
Ear trumpets are tubular or funnel-shaped devices which collect sound waves and lead them into the ear. This results in a strengthening of the sound energy impact to the eardrum and thus a better hearing for a reduced or decreased hearing individual....

, a historical form of hearing aid; indeed, his invention was almost indistinguishable in structure and function from the trumpet, which was commonly called a "microphone". The first flexible stethoscope of any sort may have been a binaural instrument with articulated joints not very clearly described in 1829. In 1840, Golding Bird
Golding Bird
Golding Bird was a British medical doctor and Fellow of the Royal College of Physicians of London. Bird became a great authority on kidney diseases and published a comprehensive paper on urinary deposits...

 described a stethoscope he had been using with a flexible tube. Bird was the first to publish a description of such a stethoscope but he noted in his paper the prior existence of an earlier design (which he thought was of little utility) which he described as the snake ear trumpet. Bird's stethoscope had a single earpiece. In 1851, Irish physician Arthur Leared invented a binaural stethoscope, and in 1852 George Cammann perfected the design of the instrument for commercial production, which has become the standard ever since. Cammann also wrote a major treatise on diagnosis by auscultation, which the refined binaural stethoscope made possible. 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 practice.

Rappaport and Sprague designed a new stethoscope in the 1940s, which became the standard by which other stethoscopes are measured, consisting of two sides, one of which is used for the respiratory system, the other for the cardiovascular system. The Rappaport-Sprague was later made by Hewlett-Packard
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...

. HP's medical products division was spun off as part of Agilent Technologies, Inc., where it became Agilent Healthcare. Agilent Healthcare was purchased by Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....

 which became Philips Medical Systems, before the walnut-boxed, $300, original Rappaport-Sprague stethoscope was finally abandoned ca. 2004, along with Philips' brand (manufactured by Andromed, of Montreal, Canada) electronic stethoscope model. The Rappaport-Sprague model stethoscope was heavy and short (18–24 in (45.7–61 cm)) with an antiquated appearance recognizable by their two large independent latex rubber tubes connecting an exposed-leaf-spring-joined-pair of opposing "f"-shaped chrome-plated brass binaural ear tubes with a dual-head chest piece.

Several other minor refinements were made to stethoscopes, until in the early 1960s Dr. David Littmann
David Littmann
David Littmann, M.D., was a German cardiologist and Harvard Medical School professor and researcher. The name Littmann is well known in the medical field for the patented Littmann Stethoscope reputed for its acoustic performances for auscultation.With Gus Machlup, Dr. David Littmann founded...

, a Harvard Medical School
Harvard Medical School
Harvard Medical School is the graduate medical school of Harvard University. It is located in the Longwood Medical Area of the Mission Hill neighborhood of Boston, Massachusetts....

 professor, created a new stethoscope that was lighter than previous models and had improved acoustics. In the late 1970s, 3M-Littmann introduced the tunable diaphragm: a very hard (G-10) glass-epoxy resin diaphragm member with an overmolded silicone flexible acoustic surround which permitted increased excursion of the diaphragm member in a "z"-axis with respect to the plane of the sound collecting area. The left shift to a lower resonant frequency increases the volume of some low frequency sounds due to the longer waves propagated by the increased excursion of the hard diaphragm member suspended in the concentric accountic surround. Conversely, restricting excursion of the diaphragm by pressing the stethoscope diaphragm surface firmly against the anatomical area overlying the physiological sounds of interest, the acoustic surround could also be used to dampen excursion of the diaphragm in response to "z"-axis pressure against a concentric fret. This raises the frequency bias by shortening the wavelength to auscultate a higher range of physiological sounds. 3-M Littmann is also credited with a collapsible mold frame for sludge molding a single column bifurcating stethoscope tube with an internal septum dividing the single column stethoscope tube into discrete left and right binaural channels (AKA "cardiology tubing"; including a covered, or internal leaf spring-binaural ear tube connector).

In 1999, Richard Deslauriers patented the first external noise reducing stethoscope, the DRG Puretone. It featured two parallel lumens containing two steel coils which dissipated infiltrating noise as inaudible heat energy. The steel coil "insulation" added .30 lb to each stethoscope. In 2005, DRG's diagnostics division was acquired by TRIMLINE Medical Products.

Current practice

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

Acoustic

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 two-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 twelve 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.

Electronic

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.
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 an Electromagnetic Diaphragm
Electromagnetic Diaphragm
Electromagnetic Diaphragm is a form of capacitive sensor used on an electronic stethoscope. The diaphragm is coated with a conductive material. Behind the diaphragm, a conductive plate is positioned behind and parallel to the diaphragm, so that the two conductive elements form a capacitor...

 with a 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
Wireless
Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...

 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
Telemedicine
Telemedicine is the use of telecommunication and information technologies in order to provide clinical health care at a distance. It helps eliminate distance barriers and can improve access to medical services that would often not be consistently available in distant rural communities...

 (remote diagnosis) and teaching.

Electronic stethoscopes are also used with Computer-aided Auscultation
Computer-aided auscultation
Computer-aided auscultation is a clinical decision support system, which is designed to assist physicians and other health professionals with decision making tasks when assessing a heart murmur. The need for computer-aided auscultation is increasing as the auscultation skills of physicians are...

 programs to analyze the recorded heart sounds pathological or innocent heart murmurs.

Recording stethoscopes

Some electronic stethoscopes feature direct audio output that can be used with an external recording device, such as a laptop or MP3
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...

 recorder. The same connection can be used to listen to the previously-recorded auscultation
Auscultation
Auscultation is the term for listening to the internal sounds of the body, usually using a stethoscope...

 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
Telemedicine
Telemedicine is the use of telecommunication and information technologies in order to provide clinical health care at a distance. It helps eliminate distance barriers and can improve access to medical services that would often not be consistently available in distant rural communities...

, or remote diagnosis.

Fetal stethoscope

A fetal stethoscope or fetoscope is an acoustic stethoscope shaped like a listening trumpet. It is placed against the abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

 of a pregnant
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

 woman to listen to the heart sounds of the fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

. The fetal stethoscope is also known as a Pinard's stethoscope or a pinard, after French obstetrician Adolphe Pinard
Adolphe Pinard
right|thumb|Adolphe Pinard Adolphe Pinard was a French obstetrician who was a native of Méry-sur-Seine. He practiced medicine in Paris, where he was an assistant to Étienne Stéphane Tarnier and a professor of obstetrics.Pinard was a pioneer of modern perinatal care and the "puericulture movement"...

(1844–1934).

Stethoscope Earpieces

Stethoscopes usually have rubber earpieces which aid comfort and create a seal with the ear improving the acoustic function of the device. Stethoscopes can be modified by replacing the standard earpieces with moulded versions which improve comfort and transmission of sound. Moulded earpieces can be cast by an audiologist or made by the stethoscope user from a kit.

Maintenance

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. Most lubricants must be kept away from rubber, vinyl, and plastic parts. Only products that have been tested to be safe and effective for cleaning stethoscopes and similar medical instruments should be used.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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