stethoscope

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Any of various instruments used for listening to sounds produced within the body.

[French stéthoscope : Greek stēthos, chest + French -scope, an instrument for viewing (from Latin -scopium; see –scope).]

Definition

The stethoscope is an instrument used for auscultation, or listening to sounds produced by the body. It is used primarily to listen to the lungs, heart, and intestinal tract. It is also used to listen to blood flow in peripheral vessels and the heart sounds of developing fetuses in pregnant women.

Purpose

A stethoscope is used to detect and study heart, lung, stomach, and other sounds in adult humans, human fetuses, and animals. Using a stethoscope, the listener can hear normal and abnormal respiratory, cardiac, pleural, arterial, venous, uterine, fetal and intestinal sounds.

Demographics

All health care providers and students learn to use a stethoscope.

Description

Stethoscopes vary in their design and material. Most are made of Y-shaped rubber tubing. This shape allows sounds to enter the device at one end, travel up the tubes and through to the ear pieces. Many stethoscopes have a two-sided sound-detecting device or head that listeners can reverse, depending on whether they need to hear high or low frequencies. Some newer models have only one pressure-sensitive head. The various types of instruments include: binaural stethoscopes, designed for use with both ears; single stethoscopes, designed for use with one ear; differential stethoscopes, which allow listeners to compare sounds at two different body sites; and electronic stethoscopes, which electronically amplify tones. Some stethoscopes are designed specifically for hearing sounds in the esophagus or fetal heartbeats.

Diagnosis/Preparation

Training

Stethoscope users must learn to assess what they hear. When listening to the heart, one must listen to the left side of the chest, where the heart is located. Specifically, the heart lies between the fourth and sixth ribs, almost directly below the breast. The stethoscope must be moved around. A health care provider should listen for different sounds coming from different locations. The bell (one side of the head) of the instrument is generally used for listening to low-pitched sounds. The diaphragm (the other side of the head) of the instrument is used to listen to different areas of the heart. The sounds from each area will be different. "Lub-dub" is the sound produced by the normal heart as it beats. Every time this sound is detected, it means that the heart is contracting once. The noises are created when the heart valves click to close. When one hears "lub," the atrioventricular valves are closing. The "dub" sound is produced by the pulmonic and aortic valves. Other heart sounds, such as a quiet "whoosh," are produced by "murmurs." These sounds are produced when there are irregularities in the path of blood flow through the heart. The sounds reflect turbulence in normal blood flow. If a valve remains closed rather than opening completely, turbulence is created and a murmur is produced. Murmurs are not uncommon; many people have them and are unaffected. They are frequently too faint to be heard and remain undetected.

The lungs and airways require different listening skills from those used to detect heart sounds. The stethoscope must be placed over the chest, and the person being examined must breathe in and out deeply and slowly. Using the bell, the listener should note different sounds in various areas of the chest. Then, the diaphragm should be used in the same way. There will be no wheezes or crackles in normal lung sounds.

Crackles or wheezes are abnormal lung sounds. When the lung rubs against the chest wall, it creates friction and a rubbing sound. When there is fluid in the lungs, crackles are heard. A high-pitched whistling sound called a wheeze is often heard when the airways are constricted.

When the stethoscope is placed over the upper left portion of the abdomen, gurgling sounds produced by the stomach and small intestines can usually be heard just below the ribs. The large intestines in the lower part of the abdomen can also be heard. The noises they make are called borborygmi and are entirely normal. Borborygmi are produced by the movement of food, gas or fecal material.

Operation

Some stethoscopes must be placed directly on the skin, while others can work effectively through clothing. For the stethoscopes with a two-part sound detecting device in the bell, listeners press the rim against the skin, using the bowl-shaped side, to hear low-pitched sounds. The other flat side, called the diaphragm, detects high-pitched sounds.

A stethoscope is used in conjunction with a device to measure blood pressure (sphygmomanometer). The stethoscope detects sounds of blood passing though an artery.

Examination with a stethoscope is noninvasive but very useful. It can assist members of the health care team in localizing problems related to the patient's complaints.

Maintenance

Stethoscopes should be cleaned after each use in order to avoid the spread of infection. This precaution is especially important when they are placed directly onto bare skin.

Aftercare

A stethoscope is a sensitive instrument. It should be handled with some care to avoid damage. It requires periodic cleaning.

Risks

There are no risks to persons being examined with a stethoscope. Users of a stethoscope may be exposed to loud noise if the bell is accidentally dropped or struck against a hard surface while the earpieces are in the user's ears.

Normal Results

Stethoscopes produce important diagnostic information when used by a person with training and experience.

Morbidity and Mortality Rates

Normal use of a stethoscope is not associated with injury to either an examiner or a person being examined.

Alternatives

A tube formed by a roll of paper will function in the same manner as a stethoscope. This improvised instrument was the first form of the modern stethoscope invented by René Laënnec (1781-1826), a French physician. An inverted glass will also function as a stethoscope by placing the open portion on the surface to be listened to and the ear of the examiner on the bottom of the glass. Due to their shape, wine glasses with stems are more effective than flat-bottomed tumblers.

See also Physical examination.

Resources

Books

Bickley, L. S., P. G. Szilagyi, and J. G. Stackhouse, eds. Bates'Guide to Physical Examination & History Taking, 8th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2002.

Blaufox, MD. An Ear to the Chest: An Illustrated History of the Evolution of the Stethoscope. Boca Raton, FL: CRC Press-Parthenon Publishers, 2001.

Duffin, J. To See with a Better Eye. Princeton, NJ: Princeton University Press, 1998.

Duke, M. Tales My Stethoscope Told Me. Santa Barbara, CA: Fithian Press, 1998.

Periodicals

Conti, C. R. "The Ultrasonic Stethoscope: The New Instrument in Cardiology?" Clinical Cardiology 25 (December 2002): 547-548.

Guinto, C. H., E. J. Bottone, J. T. Raffalli, et al. "Evaluation of Dedicated Stethoscopes as a Potential Source of Nosocomial Pathogens." American Journal of Infection Control 30 (December 2002): 499-502.

Hanna, I. R., and M. E. Silverman. "A History of Cardiac Auscultation and Some of its Contributors." American Journal of Cardiology 90 (August 1, 2002): 259-267.

Savage, G. J. "On the Stethoscope." Delaware Medical Journal 74 (October 2002): 415-416.

Organizations

American Academy of Family Physicians. 11400 Tomahawk Creek Parkway, Leawood, KS 66211-2672. (913) 906-6000. www.aafp.org. E-mail: fp@aafp.org

American Academy of Pediatrics. 141 Northwest Point Boulevard, Elk Grove Village, IL 60007-1098. (847) 434-4000; FAX: (847) 434-8000. www.aap.org. E-mail: kidsdoc @aap.org

American College of Physicians. 190 N. Independence Mall West, Philadelphia, PA 19106-1572. (800) 523-1546, x2600 or (215) 351-2600. www.acponline.org.

American College of Surgeons. 633 North St. Clair Street, Chicago, IL 60611-3231. (312) 202-5000; FAX: (312) 202-5001. www.facs.org. E-mail: postmaster@facs.org

Other

British Broadcasting Company. www.bbc.co.uk/radio4/science/guessingtubes.shtml. (March 1, 2003)

Institution of Electrical Engineers. www.iee.org/News/PressRel/z18oct2002.cfm. (March 1, 2003)

McGill University Virtual Stethoscope. www.music.mcgill.ca/auscultation/auscultation.html. (March 1, 2003)

University of Minnesota Academic Health Center. www.ahc.umn.edu/rar/MNAALAS/Steth.html. (March 1, 2003)

— L. Fleming Fallon, Jr., MD, DrPH

Background

A stethoscope is a medical instrument used to listen to sounds produced in the body, especially those that emanate from the heart and lungs. Most modern stethoscopes are binaural; that is, the instrument is intended for use with both ears. Stethoscopes comprise two flexible rubber tubes running from a valve to the earpieces. The valve also connects the tubes to the chestpiece, which can be either a bell-shaped piece to pick up low sounds or a flat disk for higher frequencies. The stethoscope is used mainly for the detection of heart murmurs, irregular heart rhythms, or abnormal heart sounds. It is also used to listen to the sound of air moving through the lungs in order to detect abnormalities in the air tubes and sacs found in the lung walls.

The universally acknowledged inventor of the stethoscope is Rene-Theophile-Hyacinthe Laennec, who, finding it difficult to listen to a patient's heartbeat unaided, rolled up a cylinder of paper, thereby amplifying the sound. Laennec had noticed, as others such as Leonardo da Vinci had before him, that sound becomes amplified to the human ear as it passes through wood. He observed children holding a piece of wood to their ears and scratching the other end. The wood increased the sound of the scratching. In 1819, Laennec provided physicians with what he originally called a baton, a hollow cylinder made from wood (walnut or such light woods as fir or boxwood) perhaps as short as 5.9 inches (15 centimeters) in length. The bore was shaped like a trumpet, but for listening to the heart, a stopper could be inserted to make the bore merely cylindrical.

The first true stethoscopes (based on Laennec 's "baton") were made of wood (usually cedar or pine) tubes that ranged in shape from cylinder- to goblet- or hourglass-shaped. The lengths ranged from 5.90 to 8.86 inches (15 to 22.5 centimeters). Unlike those of today, these stethoscopes were monaural; that is, they were held to one ear and had no ear plugs. This type of stethoscope is still used in some places in Europe. Stethoscopes of varying materials (such as hard rubber or aluminum) were common during the mid-nineteenth century. A few telescoped to provide a stethoscope of varying length. The first innovation was not at first applied to the stethoscope, but to conversation tubes and hearing aids produced by many manufacturers in the late 1800s. These items were at first horn-shaped, yet eventually included earplugs connected to rubber tubes. Designers of stethoscopes adapted such devices, and the stethoscope of the time consisted of an earplug, a flexible rubber tube, and a bell-shaped chestpiece. Despite its short-comings in the conductance of all chest sounds equally, this early stethoscope was commended for its convenient shape and flexibility.

Binaural stethoscopes increased in popularity fairly rapidly. As early as 1829 a trumpet-shaped mahogany chestpiece was screwed into a joint from which two lead pipes led to the ears. The device, invented by medical student Nicholas P. Comins, was deemed flexible (despite the rigidity of the wooden and metallic parts), because unlike the earlier monaural stethoscopes, it had movable parts.

The 1840s and 1850s saw the development of prototypes that closely resembled the stethoscope of today. In 1841 Marc-Hector Landouzy of Paris introduced a stethoscope made partly of gum elastic tubes; this proto-type was improved slightly in 1851 by Arthur Leared of Dublin. The main problem with many early designs was the inferior earpieces that provided muffled sound. George Cammann of New York perfected the nineteenth century stethoscope in 1852. His instrument, considered to be the best of the time, had ivory or ebony knobs as earpieces, and these had springs attached to hold them more securely in the ear. The tubes were made of coils of wires sandwiched between rubber that was then coated with silk or cotton. The chestpiece was surrounded by a ring of rubber, creating a suction cup that more easily adhered to the skin.

Another type of stethoscope was developed in 1859. Designed by Scott Alison, the differential stethoscope had two separate chestpieces, allowing the user to hear and compare sounds in two different places. This stethoscope also allowed the physician to better pinpoint the source of the sound through the natural process of triangulation our ears normally use to discover the direction of sounds.

The first electronic stethoscopes became available as early as the 1890s; by 1902, Albert Abrams developed a truly useable one. With it, he was able to amplify the sounds made by the heart. By applying resistance gradually to the circuit, he could eliminate certain sounds, thereby differentiating between the heart's muscular and valvular movements.

The basic form of the binaural stethoscope has remained virtually unchanged since the beginning of the twentieth century. Major advancements have been made in the type of materials used—plastics such as polyvinyl chloride and Bakelite became available; the manufacturing processes that increase the airtightness and flexibility of the stethoscope have been refined; and large scale production has been streamlined, ensuring that medical practitioners can obtain sufficient stethoscopes from a wide range of choices, and that consumers can purchase stethoscopes for home use.

Raw Materials

A binaural stethoscope consists of earplugs, binaural pieces, flexible tubing, a stem, and a chestpiece. The earplugs are attached to springs made of steel so that they fit firmly in the ears, while the earplugs themselves are made from either Delrin (a trademark plastic that is white, rigid, and similar to nylon) or softer molded silicone rubber. The binaural pieces that run from the earplugs to the flexible tubing, the stem that runs from the flexible tubing to the chestpiece, and the chestpiece itself are made from metal (aluminum, chrome-plated brass, or stainless steel). The flexible tubing is either polyvinyl chloride or latex rubber. The stem for stethoscopes with dual diaphragms has a valve with a steel ball bearing and a steel spring inside. This type of stethoscope can switch from a flat diaphragm to a cupped one when turned by shifting the ball bearing to cover up the pathway to the diaphragm that is not in use. The flat diaphragm is formed from a flat, thin, rigid plastic disk that can be Bakelite, an epoxy-fiberglass compound, or other suitable plastic. Today, most stethoscopes have an anti-chill ring attached to both sides of the diaphragm. The anti-chill ring, besides being more comfortable for the patient, allows better suction and thus allows sounds to be heard more clearly. The rings are made from either silicone rubber or polyvinyl chloride.

The Manufacturing
Process

Although the stethoscope is a simple device, it is typical for its metal parts and plastic parts to be manufactured at separate locations, and for the entire device to be assembled at yet another location. It is also common for inexpensive models to be sold disassembled. Stethoscopes are rarely custom-made. If there is a large volume sold to one customer, the manufacturer can make a certain specified color or put the name of the hospital onto the stethoscopes.

Making the metal chestpiece

• Aluminum is typically die cast. In this process, pressured molten aluminum is injected into molds, forming a slug in the form of a crude binaural piece or chestpiece. The slug is then machined to form its proper shape. Stainless steel arrives in huge rods that are machined on lathes using a semiautomatic process. Brass is also machined before being sent out for electroplating.

  The machining process consists of cutting excess metal from the slug or rod according to a plan that will yield a correctly shaped binaural piece or chestpiece. The binaural piece is then threaded at the top for the earplugs, and barbs are cut into the bottom to allow for the tubing connection. The chestpiece is also barbed at the top to allow for the connection. The metal springs are then connected and sealed to the binaural pieces.

Forming the tubes

• More expensive stethoscopes have tubing that is "dipped." The binaural pieces are repeatedly dipped into a liquid latex until the tubes are of the correct thickness. Tubes intended for inexpensive or disassembled models are molded or extruded using standard methods. To attach the separate tubing, it is first heated by placing it in warm water; next, it is pushed onto the binaural pieces, wrapping snugly around the barbs. Another less-common method of attaching the tubing is to place the binaural pieces in a mold and then place the tubing around them to form a seal.

Assembly

• Stethoscopes are hand assembled. Once the binaural pieces have tubes, the diaphragm is placed in the chestpiece and sealed. Next, the anti-chill ring is put on both sides of the chestpiece. This can be done by cutting a recess in a circular track around the rim and slipping the ring inside. The preferred method is to stretch the ring around the rim of the diaphragm or bell, making a secure fit. The earplugs are then screwed on.

Packaging

• Inexpensive stethoscopes, which may be disassembled, are placed in bags and sealed. Mid-range stethoscopes are boxed. Quality stethoscopes are placed in sturdy boxes that have spaces die-cut in the packaging into which the stethoscope and accessories fit snugly. The stethoscopes are then placed in cases that hold 20 to 50 boxes each and shipped to medical supply dealers, or, if there is a large volume, directly to a hospital. The medical supply dealers then provide stethoscopes to private practice, hospitals, medical supply stores, and drug stores.

Quality Control

A stethoscope must be able to pick up incredibly subtle, quiet sounds at such a level that a person of normal hearing can detect them using the instrument. Air leaks can decrease the volume of sound by as much as 10 to 15 decibels, as well as allow ambient noise to enter the stethoscope; therefore airtightness is imperative. Even inexpensive, disassembled stethoscopes available in drug stores easily disclose recognizable sounds (such as a heartbeat), while the highest quality instrument must meet tolerances of approximately 2.5 x 104 meters to ensure that all the pieces fit snugly and the junctions are airtight.

Air leaks are almost inevitable, and are caused by cracking, punctures, weakness of metal, or pinhole formation during the manufacturing process. To detect any problems before shipping, the manufacturer places the stethoscopes in a machine that blows a steady stream of air through each instrument. There are also tug tests for stethoscopes. The instrument is placed on a machine that pulls at a certain level of force to check whether normal use will separate the pieces.

All raw materials are also inspected, and each piece manufactured at a place other than the assembly plant is inspected for quality. Specific tolerances and procedures are checked at each step of the manufacturing and assembly process to see that the work is done correctly. The inspection consists of visually examining the stethoscope and testing the mechanical parts for proper fit and function. Every single assembled stethoscope is then checked to see if it is acoustically reliable.

Nurses, doctors, and other health care professionals undergo extensive training in auscultation so that they can interpret the sounds they hear, though most might specialize in only one or a few types of readings. For instance, somebody listening to a patient breathe must know the sounds of a healthy lung system, as well as the sounds of each type of lung dysfunction so the patient can be diagnosed correctly.

Maintenance and proper use of the stethoscope is just as important as the quality of manufacture. The stethoscope should be inspected periodically for air leaks and for defective parts that need replacing. To remove earwax and lint, the earplugs and chestpiece should be carefully wiped with rubbing alcohol, and the rest should be washed in mild, soapy water. If hospital procedure requires it, and the stethoscope can handle it, it should undergo standard sterilization procedures.

Where To Learn More

Books

Davis, Audrey B. Medicine and Its Technology. Greenwood Press, 1981.

Reiser, Stanley Joel. Medicine and the Reign of Technology. Cambridge University Press, 1978.

Periodicals

Bak, David J. "Stethoscope Allows Electronic Amplification," Design News. December 15, 1986, p. 50.

Beaumont, Estelle. "For the Latest Word on Stethoscopes: Listen Here!"Nursing78. November, 1978, pp. 33-37.

Jaffe, Joe. "Build This Doppler-Ultrasound Heart Monitor," Radio-Electronics. November, 1991, p. 49.

Reiser, Stanley Joel. "The Medical Influence of the Stethoscope," Scientific American. February, 1979, pp. 148-156.

Stone, John. "Cadence of the Heart," The New York Times Magazine. April 24, 1988, pp. 61-62.

[Article by: Rose Secrest]

The stethoscope is an instrument for listening to sounds originating within the body. It was invented in 1816 by the French physician, Rene Laennec. The older diagnostic method of direct auscultation — applying the ear to the chest wall — was known to the ancient Greeks, but had fallen out of general use. It was, however, experimented with by Jean-Nicolas Corvisart, at the end of the eighteenth century. Laennec, who had been Corvisart's student, took a special interest in chest disorders. One day, he was consulted by a young woman with the symptoms of heart disease. Still a young man, Laennec felt too embarrassed to press his head against his patient's bosom. Remembering a children's game, he picked up a sheet of paper, rolled it into a tube, and placed one end upon the woman's chest. He was able to hear the sounds of her heart and her breathing quite distinctly. The stethoscope had been invented.

Leannec experimented with various materials and shapes for his new instrument, finalizing upon a simple hollow wooden cylinder, about 25 cm long. With this tool, Laennec undertook a comprehensive investigation of the sounds emanating from the heart and lungs, correlating his findings with post-mortem results. His treatise on the subject is the basis of our modern understanding of the pathology of the lung.

While there was some early opposition, Laennec's innovation came into general use quite quickly. The development of clinical teaching in the hospitals provided students with the necessary supply of patients upon whom to practice. By the 1850s, the stethoscope had become virtually the indispensable badge of office of the medical practitioner. Its widespread adoption encouraged the development of other methods of physical diagnosis.

However, despite Laennec's claims, the stethoscope possessed only a few technical advantages over direct auscultation. In most circumstances, the instrument did not enable one to hear the thoracic sounds any more clearly than one could with the unaided ear. What it did do was enable the physician to examine the patient's chest more conveniently, more hygienically, and less intrusively. In 1828, N. P. Comins, in Edinburgh, designed a stethoscope with a hinge in the middle of its barrel, to facilitate bedside application. Comins also suggested that a binaural stethoscope might be clinically useful, and in 1851 Arthur Leared designed an instrument with two flexible rubber tubes. This was the basis of the modern stethoscope, equipped with either an open bell or a diaphragm at the chestpiece, but it did not come into common use until the 1890s. Throughout the nineteenth century, many other modifications were suggested to improve the acoustics or the ease of use of the instrument, and methods for amplifying the heart and lung sounds were investigated.

While now superseded, to a large extent, in the diagnosis of lung disorders by the X-ray machine and other imaging techniques, and of heart disorders by investigative techniques ranging from the electrocardiogram to the ultrasonic scanner, the stethoscope remains indispensible in the initial detection of abnormalities in both hospital and general practice. Numerous applications have been found outside the thoracic region, such as in the monitoring of bowel function and of pregnancy, and in the measurement of blood pressure.

— Malcolm Nicolson

See also sounds of the body.

An instrument used to assist the health professional to listen to body sounds: heart, lungs, pulse, and gastrointestinal. It consists of two earpieces connected by means of flexible tubing to a diaphragm, which is placed against the skin of the patient at a location appropriate to pick up the sound.

An instrument used in listening to internal body sounds. Most familiarly, physicians and nurses use it to listen to heart sounds.

An instrument used to hear and amplify the sounds produced by the heart, lungs and other internal organs.
The modern stethoscope is binaural, with two earpieces and flexible rubber leading to them from the two-branched opening of the bell or cone. In this way, sound travels simultaneously through both of the branches to the earpieces. See also phonendoscope.

• electronic s. — audible sounds are magnified through an amplifier to earphones, of which there may be more than one set, and may be broadcast through loudspeakers, but in both instances the results are mediocre.
• esophageal s. — one passed into the esophagus with the tip positioned at the level of the heart. It provides an excellent means of monitoring heart sounds and respiration while the animal is anesthetized.

3M Littmann Classic II Stethoscope

The stethoscope (from Greek στηθοσκόπιο, of στήθος, stéthos - chest and σκοπή, skopé - examination) is an acoustic medical device for auscultation, or listening to the internal sounds of an animal body. It is often used to listen to heart sounds. It is also used to listen to intestines and blood flow in arteries and veins. 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.

Contents 1 History 2 Current practice 3 Types of stethoscopes 3.1 Acoustic 3.2 Electronic 3.2.1 Noise reduction 3.2.2 Recording stethoscopes 3.3 Fetal stethoscope 4 Maintenance 5 See also 6 References 7 External links

History

Early stethoscopes

The stethoscope was invented in France in 1816 by René-Théophile-Hyacinthe Laennec at the Necker-Enfants Malades Hospital in Paris.^[1] It consisted of a wooden tube and was monaural. His device was similar to the common ear trumpet, 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". In 1851, 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 authored 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. The Rappaport-Sprague was later made by Hewlett-Packard. 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 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. Today there are still cardiologists who consider the original Rappaport-Sprague to be the finest acoustic stethoscope. Rappaport-Sprague copies made in China currently retail for about US$20.00. The Rappaport-Sprague model stethoscope was heavy and short (18"-24") 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, a Harvard Medical School professor, created a new stethoscope that was lighter than previous models and had improved acoustics.^[2] 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 acountic 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 ^[3] 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 .30lb to each stethoscope. In 2005, DRG's diagnostics division was acquired by TRIMLINE Medical Products.^[4] Between 1998-2007 Marc Werblud, a disabled paramedic/medical student created a lightweight 32" long acoustic noise cancelling stethoscope which improved sound quality, and reduced neck strain. The acoustic properties of the specific materials used to make stethoscope components were first tested to determine their 'resident frequency'. The results of individual acoustical component materials tests revealed how their collective interactions determine the instrument's dominant tonal character and frequency response of the stethoscope, yielding several high fidelity and acoustic noise cancelling stethoscope models. Some models weighed as little as 133 grams (4.7 oz) - half the weight of common cardiology stethoscopes from the 1960s and 1970s. The new models also included a unique set of stethoscope diaphragms which increased frequency response, and could be sanitarily changed for each patient.

Until his death in 2007, Georgetown University Professor W. Proctor Harvey (b. 1917) was the name most synonymous with the stethoscope and considered the nation's most skilled practitioner of auscultation, the ability to detect cardiac ailments by listening to the sounds of the heart. Dr. Harvey's incredible gift was being able to make sound clinical diagnoses from basic clinical examinations and the bedside using only an acoustic stethoscope. Dr. Harvey elevated the discipline of cardiovascular diagnosis to an art form. He taught differential auscultation using classical music to train a generation of clinicians to diagnose the heart by first learning to hear the individual instrument voices within a symphony. Harvey invented acoustic stethoscopes under the Tycos brand name notably, the Harvey Triple-head; and the "stethophone", the first electronic amplification auscultation device.^{[citation needed]}

Current practice

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.

Nurses, technicians, paramedics, emergency medical technicians, pharmacists, and other associated personnel may in some countries be trained to use stethoscopes to obtain basic vital signs and to listen to heart and lung sounds. A doctor will typically be notified for further assessment if something unusual is heard.

Types of stethoscopes

Acoustic

Acoustic 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]

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, 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.

Noise reduction

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.

Recording stethoscopes

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.

Fetal stethoscope

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).

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.

Be careful to use only products that have been tested to be safe and effective for cleaning stethoscopes and other medical instruments.

See also

• Doppler fetal monitor

References

1. ^ Laënnec RTH (1819). De l'auscultation médiate ou traité du diagnostic des maladies des poumon et du coeur. Paris: Brosson & Chaudé. 
2. ^ 3M.com - History of Littmann Stethoscopes at a glance
3. ^ Stethoscope Littmann Stethoscopes for Medical Students
4. ^ TRIMLINE Medical Products
5. ^ Acoustic stethoscope reviews and ratings

External links

Wikimedia Commons has media related to: Stethoscopes

• The Auscultation Assistant, - "provides heart sounds, heart murmurs, and breath sounds in order to help medical students and others improve their physical diagnosis skills"
• BBC: Smart stethoscope for detecting kidney stones

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Dansk (Danish)
n. - stetoskop

Nederlands (Dutch)
stethoscoop

Français (French)
n. - stéthoscope

Deutsch (German)
n. - Stethoskop, med. Hörrohr

Ελληνική (Greek)
n. - (ιατρ.) στηθοσκόπιο

Italiano (Italian)
stetoscopio

Português (Portuguese)
n. - estetoscópio (m)

Русский (Russian)
стетоскоп, дефектоскоп, выслушивать с помощью стетоскопа

Español (Spanish)
n. - estetoscopio

Svenska (Swedish)
n. - stetoskop

中文（简体）(Chinese (Simplified))
听诊器

中文（繁體）(Chinese (Traditional))
n. - 聽診器

한국어 (Korean)
n. - 청진기

日本語 (Japanese)
n. - 聴診器

العربيه (Arabic)
‏(الاسم) سماعه الطبيب‏

עברית (Hebrew)
n. - ‮סטתוסקופ, מסכת, אבוב-רופאים‬

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