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TABLE OF CONTENT
1.0
Introduction
1.1
Noise exposure
1.2
Epidemiology
1.3
Path physiology
1.4
Illustrative cases 1 and 2
2.0
Noise induced hearing damage
2.1
Sound that causes noise induced hearing damage
2.2
The effect of noise induced hearing damage
2.3
The symptom of noise induced hearing damage
2.4
Who is affected by noise induced hearing damage
2.5
Prevention of noise induced hearing damage
3.0
Prevention
3.1
Primary prevention
3.2
Educating and motivation of patient
3.3
Patients should be made aware of the availability of hearing protection and
ways to use it correctly
3.4
4.0
Occupational hearing conversation
Conclusion and recommendation
References
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1.0
INTRODUCTION
Hearing loss caused by exposure to recreational and occupation noise result in
devastating disability that is virtually 100 percent preventable. Noise induced hearing
damage is the second most common form of sensorineural hearing deficit after
presbycusis (age-related hearing loss). Shearing forces caused by any sound have an
impact on the stereocilla of the hair cells of the basilar membrane of the cochlea; when
excessive, these forces can cause cell death. Avoiding noise exposure stops further
progression of the damage.
Noise induced hearing damage can be prevented by avoiding excessive noise and
using hearing protection such as ear plug and ear muff.
Noise induced hearing damage is a sensorneural hearing deficit that began at the
higher frequencies (2,000 to 6,000hz) and develops gradually as a result of chronic
exposure to excessive sound levels. Although the loss is typically symmetrics noise
from such as firearms or sirens may produce an asymmetric loss.
1.1
Noise exposure
Noise perhaps is the most common occupational and environmental hazard. As
many environmental hazard. As many as 30 million Americans are exposed to
potentially harmful sound levels in their workplace. Outside of work, many
persons purse recreational activities that can produce harmful noise.
Sixty million Americans own firearms, and many use them without adequate
hearing protection, other non occupational source of noise include; chain saws
and other powerful tools, amplified music and recreational vehicles such as
snowmobile and motorcycles. Some type of toys for children can produce
sounds capable of causing permanent hearing damage.
Table 1
Common source
Sounds
Loudness (dB)
Gunshot (Peak period)
140 to 170
Jet take off
140
Rock concert, chainsaw
110 to 120
Diesel locomotive, stereo headphones
110 to 120
Motor cycles, lawn mower
90
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OSHA level for hearing
85*(8
hour
time
coverstion
program weighted average)
Converstion
60
Quiet room
50
Whisper
30 to 40
OSHA= occupational safety and health administration; dB * measurement
expressed as dB (A), a scale weighted towards sound at higher frequencies.
Noise can be described in terms of intensity (perceived as loudness) and
frequency (perceived as pitch). Both the intensity and the duration of noise
exposure determine the potential for damage to hair cells of the inner ear. Even
sounds perceived as “comfortably” loud can be harmful.
Sound intensity is measured as sound pressure level (SPL) in a logarithmic
decibel (dB) scale Table 1. noise exposure measurement are often expressed as
dB (A), a scale weighted towards sounds at higher frequencies, to which the
human ear is more sensitive. Noise can cause permanent hearing damage at
chronic exposure equal to an average SPL of 85.
dB (A) or higher for an eight hour period. Based on the logarithmic scale, a dB
increase in SPL represents a doubling of the sound intensity. Therefore four
hours of noise exposure at 88 (A) is considered to provide the same noise
“dose” as eight hours at 85dB(A), and a single gunshot which is approximately
140 to 170 dB (A), has the same sound energy as 40 hours of 90 dB (A) noise.
FIG. 1.
Diagram illustration the human ear
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1.2
Epidemiology
Noise induced hearing damage is the second most common sensorineural
hearing damage after age related hearing loss (prebycusis). Of the more than 28
million Americans with some degree of hearing impairment, as many as 10
million have hearing damage caused in part by excessive noise exposure in the
workplace or during recreational activities.
The economic costs of occupational hearing damage have been estimated to be
in the billions of dollars.
Noise induced hearing damage had been well recognized since the industrial
revolution. An early tern for the condition was “boilermakers” disease, because
so many workers who made steam boilers developed hearing loss.
In today’s noisy society, even children and young adults are at risk. A recent
study found evidence of high- frequency hearing damage in nearly one third of
a whort of college students.
1.3
Pathophysiology
Noise induced hearing damage maybe exacerbated by concurrent exposure to
ototoxic agents such as solvents or heavy metals.
To be perceived, sounds must exert a shearing force on the stereocilla of the
hair cells lining the basilar membrane of the cochlea. When excessive, this
force can lead to cellular metabolic over bad. Cell damage and cell death.
Noise- induced hearing damage therefore represents excessive “wear and tear”
on the delicate inner ear structure. Concurrent exposure to ototoxic substances,
such as solvents and heavy metals, may increase the damage potential of noise.
Once exposure to damaging noise level is discontinued, further significant
progression of hearing damage stops. Individual susceptibility to noise induced
hearing damage varies greatly, but the reason that some persons are more
resistant to it while others are more susceptible is not well understood.
Recent animals experiments suggest that free oxygen radicals may mediate
noise damage to hair cells. In the future, use of chemoprotective agents such as
anti oxidants as well as identification of host risk factors for susceptibility to
noise induced hearing damage, may enhance prevention and treatment effort.
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1.4
Illustrative cases
A “temporary threshold shift” represents transient hair cell dysfunction and
occurs in patients who have had an exposure to excessive noise
(e.g. at a rock concert). Repeated temporary threshold shifts may ultimately
cause a permanent hearing deficit
CASE 1
A teenaged girl was seen for a school physical examination. Screening
audiometry performed in the office revealed a 30- dB (mild) elevation of
hearing threshold at 4, 000hz, a confirmation audiogram taken by an
audiologist showed a sensoneural loss in a “notch” pattern at 4, 000hz figure 1.
In response to questioning, the girl reported spending several hours a day
listening to music through headphones. The previous hours at a rock concert
without wearing hearing protectors. Afterwards, she noticed and “felt like there
was cotton in them”. Several days later, her hearing had returned to normal.
This patient is an example of a person who has experienced a “temporary
threshold shift”. Temporary threshold shift are common in persons exposed to
excessive noise and they represent transient hair cell dysfunction. Although
complete recovery from a given episodes of such shifts occurring after noise
exposures give way to permanent threshold shifts because hair cells in the
cochlea are progressively lost.
FIG 2: illustrative Audio graph findings for case
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CASE 2
A 55 years old factory worker consulted his family physician because of
ringing in his ears and depression that began soon after the onset of the tinnitus.
He had seldom worn hearing protection at work, where he has to shalet to
communicate with co- workers. Away from work, he had difficulty
understanding conversations in crowded rooms and he said he often argued
with is wife about the volume of the television set. His physician findings were
normal. An office audiogram showed a high frequency hearing damage. The
patient was referred to and audiologist, who confirmed a sensor neural hearing
loss that has probably caused by excessive noise exposure, with superimposed
age related changes. A hearing aid was prescribed.
The case shows that noise induced hearing damage can interfere with speech
discrimination and social functioning. The high frequency deficit causes
difficulty in perceiving and differentiating consonants sounds; patients often
report that words “run together”. High pitched sounds, such as a baby crying or
a distant telephone ringing, may not be perceived at all. Tinnitus is a common
symptom of noise overexposure and if further interferes with hearing activity,
depression and increased risks of ancients.
FIG. 3 An office audiogram
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2.0
NOISE INDUCED HEARING DAMAGE
2.1
Sound That Causes Noise Induced Damage
Noise induced hearing damage can be caused by a one-time exposure to an
intense ‘impulse’ sound such as an explosion, or by continuous exposure to
loud sound over an extended period of time, such as noise generated in a loud
working shop.
Sound is measured in units called, decibels. On the decibel scale, an increase of
10 means that a sound is 10 times more intense, or powerful, or powerful. To
your ears it sounds twice as loud. The humming of a refrigerator is 45decibels,
normal conversation is approximately 60 decibels and the noise from heavy
city traffic can reach 85 decibel. Sources of noise can cause NIHD include
motorcycles firecrackers and small firearms, all emitting sound from 120 to
150 decibel long or repeated exposure to sound at or above 85 decibel can
cause hearing loss. The louder the noise, the shorter the time period before
noise induced hearing damage can occur. Sound of less than 75 decibels, even
after long exposures are unlikely to cause hearing loss. Although being aware
of decibel levels is an important factor in protecting ones hearing, distance
from the source of the sound and duration of exposure to the sound are equally
important. A good role of thumb is to avoid noises that are “too loud” or too
close” or “too long”.
2.2
Effects of Noise Induced Hearing Damage
Exposure to harmful sounds causes damage to the hair cells as well as the
auditory or hearing nerve.
Impulse sound can result in immediate hearing loss that may be permanent.
This kind of hearing damage may be accompanied by tinnitus – a ringing
buzzing or roaring in the ears or head, which may subside overtime. Hearing
loss and tinnitus may be experienced in one or both ears, and tinnitus may
continue constantly or occasionally throughout a lifetime.
Continuous exposure to loud noise also can damage the structure of hair cells,
resulting in hearing loss and tinnitus, although the process occurs more
gradually than for impulse noise.
Exposure to impulse and continuous noise may cause only a temporary hearing
damage. If a person regains hearing, the temporary hearing loss is called a
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temporary threshold shift. A temporary threshold shift largely disappears 16 to
48 hours after exposure to loud noise. You can prevent NIHD from both
impulse and continuous noise by regularly using hearing protectors such as
earplugs or earmuffs.
Scientists believe that depending on the type of noise, the pure force of
abrations from noise can cause hearing damage. Recent studies also show that
exposure to harmful noise level triggers the formation of molecules inside the
ear that damage hair cells and result in NIHD. These destructive molecules
play an important role in hearing damage in children and adults who listen to
loud noise for too long.
2.3
Symptoms of Noise-Induced Hearing Damage (NIHD)
When a person is exposed to loud noise over a long period of time, symptoms
of NIHD will increase gradually over time, the sounds a person hear may
become distorted or muffled, and it may be difficult for the person to
understand speech. Some with NIHD may not even be aware of the loss, but it
can be detected with a hearing test.
Physician providing occupational health services to a company may supervise
the hearing conversation programme, review abnormal audiograms and advice
the programme administrator. A worker whose audiogram shows a “standard
threshold shift” (worsening 10dB on average at 2000, 3000 and 4000 Hz when
compared with the employee’s baseline test) must be notified and receive
additional training and evaluation
2.4
Who is affected by noise induced hearing damage (NIHD)
People of all ages, including children, teen, young adults and other people, can
develop NIHD. Approximately 15% of Americans between the ages 20 and 69
or 26 million Americans have high frequency hearing loss that may have been
exposed to loud sound or noise at work or in leisure activities. Recreational
activities that can put someone at risk for NIHD include target shooting and
hunting, snow mobile riding, woodworking and other hobbies, playing in a
band, and attending rock concert. Harmful noise at home may come from
lawnmowers, leaf blowers and shop tools.
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2.5
Prevention of noise induced hearing damage
NIHD is 100 percent preventable. All individual should understand the hazards
of noise and how to practice good hearing health in everyday life. To protect
your hearing, know which noise can cause damage (those at or above 85
decibel) wear earplugs or other hearing protective devices when involved in a
loud activity (special earplugs and earmuffs are available at hardware and
sporting goods stores). Be alert to hazardous noise in the environment; protect
the ears of children who are too young to protect their own. Make family,
friends and colleague aware of the hazards of noise.
Hearing Processes
Hearing depends on a series of events that change sound waves in the hear into
electrical signals. Our auditory nerve then transmits these signals to the brain
through a complex series of steps.
Sound waves enter the outer ear and travel through a narrow passage way
called the ear canal, which leads to the eardrum. The eardrum vibrates from the
incoming sound waves and sends these vibrations to three tiny bones in the
middle ear. These bones are called the malleus, incus, and stapes. The bones in
the middle ear amplify or increase the sound vibrations and send them to the
inner ear also called the cochlea, splitting it into an upper and lower part this
membrane is called “basilar” membrane, because it serves as the base or
ground floor, on which key hearing structures sit. The sound vibrations cause
the fluid inside the cochlea to ripple, and a traveling wave forms along the
basilar membrane. Hear cells, sensory cells sitting on top of the membrane
“rides the wave”.
As the hair cells move up and down, their bristly structures bump up against an
overlying membrane and tilt to one side. This tilting action cause pores like
channels, which are in the surface of the bristles, to open up. When that
happens, certain chemicals rush in, creating an electrical signal.
The auditory nerve carries these electrical signals to the brain, which translates
it into a “sound” that we recognize and understand.
Hair cells near the base of the cochlea detect higher-pitched sound, such as a
cell phone ringing. Those nearer the apex, or outermost point, detect lowerpitched sounds, such as a large dog barking
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3.0
PREVENTION
3.1
Primary Prevention
Although no studies have evaluated the efficacy of educating patient about
noise induced hearing loss, family physicians can easily screen for excessive
noise exposure during health maintenance visits seen in Table 2
An example of a screening question is “are you exposed to excessive noise in
your work place or through music or hobbies? During well child visits, parents
can be asked whether the child plays with noisy toys.
Adolescents and their parents should be counseled about exposure to amplified
music. Adults should be asked about firearms, noisy hobbies and noise
exposure at work. A positive response to the “shout” test that is, if a person
gives an affirmative answer when asked whether it is necessary to shout to
converse with someone it aims at, length in the workplace- indicates a
potentially hazardous noise level.
Table 2
Screening for noise-induced hearing damage and prevention strategies
Condition
Screening techniques
Preventive techniques
Excessive noise exposure history: are you exposed to excessive noise in your
workplace or through music or hobbies
“Short test”, do you often have to shout to talk to someone at arms length
because it is so noisy around you?
Specific sources of noise; firearms, loud music, motor cycles, snowmobiles,
power tools. Having protection; “How often do you use earplugs, earmuffs,
etc?
3.2
Educating and Motivating Patients
“Hearing health” is part of a healthy lifestyle. noise induced hearing damage is
permanent and only partially treatable, yet virtually 100% preventable.
Excessive noise should be prevented when possible. Hearing protection should
be used correctly and consistently during exposure to excessive noise.
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3.3
Awareness of the availability of hearing protectors
Patients should be made aware of the availability of the hearing protectors and
the possible way of correctly utilizing them.
Hearing impairment, do you have any difficulty with understanding speech in
noisy environment? Do you need to turn up the television volume? Do you ask
to repeat sentences? Is your hearing not as good as it was10years ago? have
family members noticed a problem with your hearing?
Physical examination; otosiopic examination Rinne and weber turning fork test
others include; office adiometry, tympanometry. Meter patient to audiologist/
otolaryngologist. If hearing loss is strongly suspected, encourage patient to
seek treatment. Assist patient and family in coping with hearing deficit. Advice
patient to use hearing protection and avoid excessive noise (lifelong) to limit
further hearing damage.
A patient reports significant exposure to noise should be inferred that noise
induced hearing damage, although permanent and not fully treatable, is
virtually 100% preventable. The clinician can motivate patients to maintain
their hearing health and thereby reduce the risk of hearing disability as they
grow older. Key factors in this efforts are living to avoid excessive noise when
possible and correctly using hearing protection when necessary. Hearing
protectors indicating earmuffs, disposable earplugs and custom-fitted earplugs,
can provide 20 to 40 dB of attenuation when used correctly. Physicians can
obtain samples from manufacturers and keep them in the office for distribution
and demonstration of techniques for proper use.
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CONCLUSION
Noise-induced hearing damage results from a single or several exposures to relatively few or
intense level of sound or noise, which affects hearing in four major ways: Acoustic trauma,
temporary threshold shift (TTS), permanent threshold shift (PTS) and Tinnitus.
RECOMMENDATION
Planning of the environment such as workplace should be properly carried out before citing of
any industry in order to prevent future occurrences of noise-induced hearing damage.
Adequate enlightenment should be made on how to prevent noise-induced hearing damage to
the hearing system. This could be achieved by educating and motivating the people on the
effect of exposure to excessive noise and how they could possibly minimize or completely
prevent exposure to excessive noise.
The use of artificial hearing protectors should be encourage in industries where exposure to
excessive noise can not be avoided. Hearing protectors such as earplugs, earmuffs, etc.
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REFERENCES
Callender, J.H. (1974) Time-Saver Standards for Architectural design data.
McGraw-hill Book
Evans, M.(1980) Housing, Climate and Comfort. The Architectural Press,
London
Microsoft Student Encarta 2008
www.nidcd.nih.gov/../noise.asp
www.aafp.org/afp/20000501/2749.html
www.dangerousdecibels.org/hearinglo
www.medicinenet.com/../article.htm
www.hearinglossweb.com
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