Stethoscope

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

• 1 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

• 2 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

• 3 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

• 4 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.

—Rose Secrest

Stethoscope

Definition
Purpose
Demographics
Description
Diagnosis/Preparation
Aftercare
Risks
Normal results
Morbidity and mortality rates
Alternatives

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.

KEY TERMS

Atrioventricular— Referring to the valves regulating blood flow from the upper chambers of the heart (atria) to the lower chambers (ventricles). There are two such valves, one connecting the right atrium and ventricle and one connecting the left atrium and ventricle.

Auscultation— The act of listening to sounds produced by the body.

Bell— The cup-shaped portion of the head of a stethoscope, useful for detecting low-pitched sounds.

Borborygmi— Sounds created by the passage of food, gas or fecal material in the stomach or intestines.

Diaphragm— The flat-shaped portion of the head of a stethoscope, useful for detecting high-pitched sounds.

Murmur— The sound made as blood moves through the heart when there is turbulence in the flow of blood through a blood vessel, or if a valve does not completely close.

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.

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?

Any member of a health care team participating in a physical examination uses a stethoscope. It is used to detect and transmit sounds created within the body.

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 Rene Laennec (1781-1826), a French physician. An inverted glass will also function as a stethoscope by placing the open portion on the

QUESTIONS TO ASK THE DOCTOR

Are the sounds being heard normal or abnormal?

Have the sounds changed since the last examination?

Has a murmur, if present, changed in pitch or loudness?

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.

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. E-mail: [email protected]. www.aafp.org.

American Academy of Pediatrics. 141 Northwest Point Boulevard, Elk Grove Village, IL 60007-1098. (847) 434-4000. Fax: (847) 434-8000. E-mail: [email protected]. www.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. E-mail: [email protected]. www.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

Stomach resection seeGastrectomy

Stomach stapling seeVertical banded gastroplasty

Stomach tube insertion seeGastrostomy

Strabismus repair seeEye muscle surgery

Stethoscope

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: [email protected]

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: [email protected]

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

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?

Any member of a health care team participating in a physical examination uses a stethoscope. It is used to detect and transmit sounds created within the body.

QUESTIONS TO ASK THE DOCTOR

• Are the sounds being heard normal or abnormal?
• Have the sounds changed since the last examination?
• Has a murmur, if present, changed in pitch or loudness?

Stethoscope

Definition

The stethoscope is an instrument used to listen to sounds produced by the body. It is used to listen to the lungs, heart, and intestinal tract.

Purpose

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

Description

Stethoscopes vary in their design and material. Most are made of rubber tubing, shaped in a "Y," allowing sound 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, which listeners flip, depending on whether they need to hear high or low frequencies. However, some of the newer models have one pressure-sensitive head. The various types of stethoscopes include: binaural stethoscopes, designed for use with both ears; single, designed for use with one ear; differential, with which listeners can compare sounds at two different body sites; and electronic, which electronically amplify tones. Some stethoscopes are designed specifically for hearing the fetal heartbeat or esophagus.

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 at the end, 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.

Maintenance

In order to avoid the spread of infection, stethoscopes should be cleaned after each use—especially when placed directly on the patient's skin.

Health Care Team Roles

Everyone on the health care team uses a stethoscope, as the provider may need to listen to sounds produced by the heart, lungs, stomach, or another body organ often.

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, it is between the fourth and sixth ribs, almost directly below the breast. The stethoscope must be moved around; the health care provider should listen for different sounds emanating from different locations. The bell of the instrument—generally used to listen to sounds of low pitch, and then its diaphragm—should be used to listen to different areas of the heart. The sounds will be different. "Lub-dub" is the sound produced by the normal heart. Every time this sound is detected, it means that the heart is contracting one time. The noises represent the heart valves clicking to close. When one hears "lub," the atrioventricular valves are closing, and "dub" means the pulmonic and aortic valves are closing. Other heart sounds, such as the quiet "whoosh," heard after "lub-dub," reflect the existence of a "murmur." These are heard when the blood moves through the heart, and mean that there is "turbulence" in the blood flow. If a valve remains closed, rather than opening completely, one might hear a murmur. These are not at all uncommon; in fact, many people have them and are unaffected.

The lungs and airways require different listening skills than those used to detect heart sounds. The stethoscope must be placed over the chest, and the patient must breathe in and out deeply, and slowly. Using the bell, the different sounds should be noted 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. When performing "percussion," on the chest, the health care practitioner should be listening for sounds made by sounds the patient makes. One would lightly "thump" around the stethoscope, against the chest, with one finger. Lungs that sound hollow are normal; they have no air in them. Lungs that have a more solid sound appear dead. On percussion, this "dead" sound may be solidification of the lung. In this case, one might make an initial diagnosis of pneumonia.

When crackles or wheezes are detected, the practitioner is hearing lung sounds that are abnormal. When the chest wall is being rubbed by the lung, "friction rubs" are detected. When there is fluid in the lungs, crackles will be heard. This is often heard when the patient has pneumonia or pulmonary edema. A high-pitched whistling sound (a wheeze) is often heard when there is pneumonia or when an airway disease (like bronchitis) is present. Lastly, an infection between the lung and the chest might produce the friction rubs—squeaky noises that infections like pleuritis (an infection between the lung and chest wall) produce.

To listen to the abdomen, the stethoscope should be held over its upper left side. One can hear "gurgling" just under the ribs. The intestines, in the lower part of the abdomen, can also be heard. The noises they make are "borborygmus"—and they are normal. The abdomen is also a site where percussion can be heard. If one thumps all around the bell of the stethoscope, the individual will hear a solid sound, as if the organ is "dead." When the sound is hollow, it means that the intestinal tract has gas in it.

Despite these somewhat basic instructions, it takes experience and skill to determine what tests might be needed once examination with the stethoscope has been completed. Examination with this instrument is particularly noninvasive, but useful. It can assist the physician and health care team in localizing the problem about which the patient is complaining.

KEY TERMS

Murmur— A murmur may be heard as blood moves through the heart, when there is "turbulence" in the flow of blood; if a valve remains closed (does not open completely) a murmur might be heard.

Pleuritis— An infection between the lung and the chest wall.

Pulmonary edema— The buildup of fluid in the lungs or respiratory system. Usually results from an increase in pulmonary capillary pressure.

Stethoscope— An instrument used to listen to bodily sounds; used to listen to the lungs, heart, and intestinal tract.

Resources

BOOKS

Nettina, Sandra, ed. Lippincott Manual of Nursing Practice. 7th ed. Philadelphia: Lippincott, 2001, p. 52.

OTHER

A Beginner's Guide to Using a Stethoscope. 〈http://www.ahc.umn.edu〉. Accessed June 28, 2001.

Masoaka, Shirley, R. N., president. UltraScope, Inc. Charlotte, NC. (800) 677-2673.

Medscape dictionary online, Merriam-Webster. 〈http://www.dict.medscape.com〉. Accessed June 30, 2001.

stethoscope 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