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NOISE-INDUCED HEARING
LOSS
Dr. Supreet Singh Nayyar, AFMC
For more presentations, visit www.nayyarENT.com
14-Jul-12
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LAYOUT
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Historical perspective
Noise & effects of noise on hearing
Mechanism & clinical features of NIHL
Early detection and prevention of NIHL
Noise and the armed forces
Recent advances
Legal and social issues in relation to NIHL
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Historical perspective
• Bronze age
• 1713, Ramazzini found hearing loss in coppersmiths
who hammered copper for their living.
• 1886 the first epidemiological survey of NIHL was
conducted by Thomas Barr
• 1890 Habermann described the histology of NIHL in
organ of corti .
• 1928 Fowler observed the typical dip at 4 KHz due to
NIHL
• 1939 Bunch published the first audiometric feature of
NIHL demonstrating the typical high frequency
SNHL
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Noise
• Noise is unwanted sound which may damage A
person’s hearing
• Temporal pattern of environmental noise can be
continuous (steady state), fluctuating, impulsive or
intermittent
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Assessing Noise Levels
• Duration, frequency and sound pressure levels
• Sound Level Meter (SLM)
• Noise Dose Meter (NDM)
• The meter is designed to measure a frequency
weighted and time-weighted value of the sound
pressure level
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General Aim Of A Noise Assessment
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I•dentify
•Obtain information
•Effectiveness of measures taken
•Choose appropriate personal hearing protectors
•Define hearing protection areas at work
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Excessive Noise
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A heavy truck is about 85 db,
A jet taking off is about 120 db.
Suction and drill during ear surgery 91-108 dB.
MRI units 90 dB.
Peak sound level in entertainment clubs
140dB
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Effects Of Noise On Hearing
• Either reversible or permanent inner ear damage
• Auditory or non-auditory.
• Effects can happen with both high and low level
noise
• Tinnitus
• Loss of hearing as well as health effects
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Auditory Effects Of Noise
• Auditory adaptation
• Noise induced temporary threshold shift
(NITTS)
• Noise induced Permanent threshold shift
(NIPTS)
• Acoustic trauma
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Adaptation
• An immediate physiological phenomenon that
occurs whenever the ear is stimulated by
sound.
• For sounds up to 70 db spl, recovery occurs in
less than half a second.
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Acoustic trauma
• A condition when there is a sudden damage to the
ear due to intense short term exposure or even a
single exposure to a very high intensity noise
• Usually occurs from fireworks, small arms fire, gun
fire and explosion. This not only results in some
damage to inner ear but also can damage the
tympanic membrane and ear ossicles
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Noise Induced Temporary Threshold Shift
(NITTS)
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Exposure to moderately intense sounds
A short term elevation of hearing thresholds
Associated with other auditory symptoms
Measured in minutes and days
The amount of TTS is directly proportional to the
intensity of sound and duration of exposure
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Noise Induced Permanent Threshold Shift
(NIPTS)
• Permanent elevation of hearing threshold due to
chronic exposure to moderately intense noise
• Permanent structural damage to the critical
elements of the cochlea
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Factors Affecting The Development Of
NIPTS
• Physical factors- intensity, duration of noise.
• Biological factors – individual susceptibility, age,
sex, genetic and social predisposition, acoustic
reflex, pre exposure threshold
• Pathological factors –drugs and chemicals, other
co existing ear diseases.
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Intensity of exposure
• Most studies have
found exponential
increase in hearing
losses with increasing
intensities
• Damage risk criteria
regarding safe level
duration of exposure
have been established
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Duration Of Exposure
• An average work place exposure of 90-94 dB
everyday over a period 10 years, NIHL reaches
its maximum and remains constant thereafter.
• Hearing loss in the higher frequencies will stop
progressing but it will spread gradually to lower
frequencies.
• Hearing loss occurs early in the first 2-3 years
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Individual susceptibility
• Certain biologic characters unique to the
individual
• Potentially important variables have been
investigated
• No evidence to suggest that there is any
relationship between age and susceptibility to
NIHL
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Role of Acoustic Reflex
• Variability in fatiguability of acoustic reflex may be one
of the factors in individual susceptibility to noise
trauma
• Documented that subjects with poor acoustic reflex
recorded a large TTS after exposure to noise
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Effect Of Melanin
• Melanin in stria vascularis of cochlea may have a
protective effect against noise
• People with blue and light colored iris may be more
susceptible to NIHL
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Drugs And Chemicals
• Combination of noise and aminoglycosides
• Additional hearing loss may take place when
humans are treated with aspirin and other
NSAID’s and exposed to high intensity noise
concomitantly.
• Environmental pollutants
• Chemical pollutants or chemical intermediaries
in industries like toluene, hexa methyl mercury
and lead acetate
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Sociacusis
• Urban setting transportation is the main cause
• A worker who is exposed to sound levels of 88
dB for 8 hours, who is then exposed to 94 dBA
sounds while commuting to and from work is at
risk of developing NIHL due to additive effects of
sound
• Recreational noise, personal stereos and CD
players can also be potentially harmful
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Medical noise
• MRI units may produce sound levels at patients
head in excess of 90 dB
• Sound levels produced by drills and suction
units during ear surgery are high enough to
produce NIHL, ranging from 91- 108 dB
• Amplified noise in powerful hearing aids
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Mechanisms for NIHL - theories :
• Mechanical/structural
damage, ranging from
disturbance of the delicate
stereocilia to tearing of the
organ of corti and
eventually permanent haircell loss, caused by severe
motion of basilar
membrane due to excessive
noise
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Mechanisms for NIHL - theories :
• Exposure to extremely intense noise (130dB)
results in necrotic-cell death process
• Metabolic exhaustion (overstimulation) of hair
cells may lead to excessive release of glutamate,
which may contribute to NIHL by causing swelling
of auditory nerve terminals
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Mechanisms for NIHL - theories :
• Severe vascular narrowing and ischemia of
cochlear microvasculature due to excessive noise
exposure
• Ionic imbalance and cellular damage due to
disruption of ionic gradients of cochlear structures
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Specific features of NIHL
• Permanent SNHL with damage predominantly to outer
hair cells (OHCs).
• History of long term exposure to dangerous noise levels
(> 85 dB for 8 hours per day)
• Gradual loss of hearing over 5-10 years of exposure
• Hearing loss initially involving higher frequencies 3-8
kHz before involving frequencies below 2KHz and below
• Speech recognition scores that are consistent with
audiometric pattern
• Hearing stabilizes once the noise exposure is terminated
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Audiometric configuration- acoustic notch
AUDIOGRAM
Test Frequency
Hearing Threshold (dB)
125
250
500
1000
2000
4000
8000
-10
0
10
20
30
40
50
60
70
80
90
100
110
120
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Otoacoustic emission (OAE) in NIHL
• The fact that OAEs are primarily generated by
OHCs assumes great significance as noise
primarily destroys the OHCs of cochlea in NIHL
• Therefore this investigative modality offers
exciting prospects for early diagnosis of NIHL and
possible detection of susceptible individuals
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Diagnosis
• Diagnosis, which is circumstantial, is largely
based on a careful history, physical examination
and appropriate audiometric evaluation, and is
frequently made by exclusion
• Noise exposure has been adequate, and there is
an appropriate hearing loss, it is customary to
attribute the loss to that cause
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Damage Risk Factors
• Intensity of sound and duration of exposure.
• Equal amounts of sound exposure produce equal amounts
of damage whether sound exposure is spread over a short
or long period.
• Important to know that with a 90 dBA sound exposure for 8
hours a day, 5 days a week, 15% of the population is at risk
for significant hearing loss after 10 years of exposure, and
that for 85 dBA exposure 8 hours a day, 5 days a week, after
10 years, only 7% of the population is at risk
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Noise and Armed forces
• Personnel of the armed forces are exposed to
very high intensity noise produced as a result of
the weapon that they use, the mechanical
transport, aircraft and ships
• Nature of their occupation exposes them to
noise levels that can jeopardize their hearing
• Exposure to a combination of steady state noise
and impulse noise of very high intensities and
their unprotected ears are vulnerable to
extensive hearing damage
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Noise and Armed forces
• In armed forces, personnel serving in certain branches
and trades are more vulnerable.
• In the army the infantry, artillery , armoured corps and
engineers are at higher risk of developing NIHL
• In the air force the pilots, air handlers and air craft
maintenance personnel are at higher risk.
• In the navy, engine room sailors, gunnery crew, air craft
carrier personnel and divers and submariners are at
higher risk of developing NIHL due to nature of their
jobs
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Noise in shooting ranges
• Nature of firing a firearm: produces very high
peak sound pressure levels even with small calibers
• These peak levels cause impulsive sound to reach
the inner ear and because of the characteristics of
impulsive type sounds, our ears are more prone to
hearing damage than with sounds emitted from
operating machines
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Typical noise levels from firearms
Outdoor range
• pistol cal. 22 @ 10 m to the side 127 - 129dB peak(C)
• rifle cal 7.62 mm @ 2 m to the side 154 – 158dB peak(C)
• rifle cal 5.56 mm @ ear level 156 - 157dB peak(C)
• revolver cal .38 @ ear level 149 – 153dB peak(C)
Indoor range
• pistol cal .38 @ approx. 1.5 m behind 145 – 147dB peak(C)
• pistol 9 mm @ approx. 1.5 m behind 147 - 149dB peak(C)
• 12 gauge pump action shotgun 150 – 151dB peak(C)
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Treatment
• NIHL unfortunately cannot be cured but it
probably is the single largest cause of
preventable deafness all over the world
• Experimental treatment modalities like
antioxidant therapy need further evaluation
• Rehabilitation with hearing aids is an excellent
option in improving the communication status of
people suffering from NIHL
• Advanced digital and programmable hearing aids
offer very good quality of hearing improvement
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Prevention
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Noise hazard identification
Engineering controls
Personal hearing protection
Monitoring audiology
Record keeping
Health education
Enforcement
Programme evaluation
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Dealing With Noise Hazards
• Carry out a risk assessment to determine the
risks from noise exposure
• •Develop a noise control policy and a hearing
conservation program
• •Provide workers with information and training
on noise, the risks from noise exposure
• Control measures put in place at the workplace
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Personal Hearing Protectors
• A device, or pair of devices, designed to be worn over (ear
muffs) or inserted in the ears (earplugs) of a person to protect
hearing
• Vary considerably in effectiveness and is highly frequency
dependent
• Earplugs reduces the noise reaching the middle ear by 15 to 30
db and work best for the mid to higher frequency region (i.e. 25 kHz)
• Earmuffs attenuate the noise by 30 to 40 db.
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Personal Hearing Protectors
• Personal hearing protectors are most vital for
prevention of NIHL
• The most important aspect of personal hearing
protectors is the regularity of use
• Most important aspect of choosing a hearing
protector device is worker comfort and confidence of
the worker using it
• A large variety of personal hearing protectors like ear
plugs, ear muffs and canal caps are available with
varying degrees of attenuation
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WHO Recommendation
• National programme for prevention of noise-induced hearing loss
should be established in all countries and integrated with primary
health care. This should include environmental and medical
surveillance, noise reduction, effective legislation, inspection,
enforcement, health promotion and education, hearing
conservation, compensation and training
• Prevention of NIHL must be appropriate, adequate, acceptable
and affordable
• Most of the population of developing countries is ignorant of the
hazards of excessive noise exposure. Awareness must be
increased about the harmful effects of noise and about its
prevention and control of NIHL
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WHO Recommendation
• There is acute shortage of reliable epidemiological data
on prevalence, risk factors and costs of NIHL from
developing countries. There is an urgent need of
structured and controlled studies in this regard.
• Research needs to be focused on pathophysiology,
technical measures for noise reduction, improving
personal hearing protectors and low cost medications
for prevention
• Communication and collaboration should be
strengthened between developed and developing
countries to facilitate research and development in this
field
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Legislations: Noise control policy
An important step in managing noise in the workplace is the
development of a noise control policy which should cover the
following issues:
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•Goals for noise exposure and peak noise levels
Design goals for new workplaces and plant
•Selection and purchase of quiet plant
•Noise controls for temporary work areas and situations
•Agreements with contractors for the responsibility of noise control and
provision of information
– •Audiometric testing and availability of records
– •Funding for a hearing conservation program
– •Period of review for the hearing conservation program
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Permitted hours of exposure at work place
Hrs permitted
Leq
LOSHA
16
8
4
2
1
0.5
0.25
87 dB
90 db
93 dB
96 dB
99 dB
102 dB
105 dB
85 dB
90 dB
95 dB
100 dB
105 dB
110 dB
115 dB
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Ambient Noise standards and Guidelines in India
Area code
Category of area
A
B
C
D
Industrial area
Commercial area
Residential area
Silence Zone
Limits in dB(A) Leq
Day
Night
75
70
65
55
55
45
50
40
• Ambient noise standards published in Gazette of India no 643 dt 26.12.89,
Succeeded by the Noise pollution (Regulation and control ) rules, 2000(Gazette of
India, vide SOI 123(E) dated 14-12-2000 and subsequently amended vide SO 1046
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(E)
dated 22-11-2000.
Noise standards for Domestic appliances
and construction equipments in India
Category
Window air-conditioners 1 ton & above
Air coolers
Refrigerators
Diesel generators foe domestic purposes
Compact rollers, front loaders, concrete
mixers, cranes, vibrators and saws
Noise limit
dB(A)
68
60
46
85-90
75
• Noise standards for Domestic appliances and construction
equipment as notified under Environment (Protection) Rules, 1986,
by G.S.R 742 (E) dated 30-8-90 and subsequently amended by GSR
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422
(E) dated 19 May 1993 www.nayyarENT.com
Noise limits for vehicles in India
Type of vehicle
Two wheeler displacement up to 80 cm3
Displacement more than 80 cm3 but less than 175 cm3
Displacement more than 175 cm3
Three wheeler
Displacement up to 175 cm3
Displacement more than 175 cm3
Passenger car
Passenger or commercial vehicle
Gross weight up to 4 tonne
Gross vehicle weight more than 4 tonne but up to 12
tonne
Gross vehicle weight more than 12 tonne
NoiseLimits
dB(A)
75
77
80
77
80
75
77
80
82
• Noise limits for vehicles from Jan 2003 as notified under Environment
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(Protection)
Rules, 1996, by GSR 742(E)
dated 25 Sep 2000
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Research on NIHL
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Hair cell regeneration
Genetic and molecular basis for NIHL
Protection from conditioning the cochlear-efferent
system
Antioxidant therapy for NIHL and acoustic trauma
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Hair cell regeneration
• Recent results using in vitro cultures of neonatal
mouse cochleas showed that over expression of
mammalian atonal homolog 1 or Math 1 , a basic
helix-loop-helix transcription factor known to be
necessary for hair cell differentiation during
development, leads to an increase in the production of
extra numerary hair cells.
• It appears that certain cells in the mammalian organ of
Corti can, at least in young animals, be redirected
towards a hair cell fate by the over expression of Math
1
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Hair cell regeneration
• Recent studies discovered that new hair cells
can be grown in a mature mammalian ear
using the Math 1 gene.
• Math 1 gene can direct hair cell
differentiation in mature nonsensory cells
and that adenoviral gene therapy will some
day likely lead to a treatment of NIHL.
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Genetic and molecular basis for NIHL
• Effort being made to find out if there are genetic factor
in the susceptibility to NIHL
• It has been seen that some strains of inbred mice are
more susceptible to NIHL than others
• Efforts to isolate a NIHL gene to a chromosomal loci
• A recessive gene that is responsible for premature age
related hearing loss has been shown to be related to
excessive susceptibility to NIHL
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Protection from conditioning
• “exposure experience” pre exposure of low to
moderate intensity sounds toughen or condition
the ear and offer protection against subsequent
harmful effects of high intensity noise
• Recent studies have demonstrated
“conditioning” effect or the development of
“resistance” in human subjects
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Antioxidant therapy for NIHL
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N-L-acetylcysteine
Acetyl-L-carnitine
Carbanathione
Glutathione ( GSH )
Allopurinol
GSH peroxidase
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Non-auditory Effects Of Noise
• Interference with communication
• Interference with efficiency and work output
• Psychological effects like irritability and
annoyance
• Disturbance to sleep, rest and thereby
contributing to fatigue
• Hypertension, peptic ulcer etc and other
systemic illnesses
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Role of the Otolaryngologist
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To identify the cause and extent of NIHL
Educate the patient
Preventive measures
Aural rehabilitation
Counseling the patient
Teach the patient to guard against further loss
Expert witness
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Conclusion
• NIHL is the single most important cause for preventable
hearing loss in this world today.
• It is to be appreciated that it is practically impossible to
reduce noise levels in industry and in our cities to safe
enough levels for infinite exposure.
• Educating people about adverse effects of noise and its
prevention and the use of personal hearing protective
devices are the major strategies against NIHL
• There is an urgent need to hasten research on the
fundamental mechanisms involved in NIHL so that
preventive and curative measures to reduce or mitigate
the permanent hearing damage due noise are evolved
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References
• Scott-Brown’s Otorhinolaryngology, editor
Michael Gleeson, 7th edition.
• Otolaryngology Head and Neck Surgery, editor
Charles W. Cummings, 4th edition.
• Ballenger’s Otorhinolaryngology Head and
Neck Surgery, editor James B. Snow Jr, John
Jacob Ballenger, 16th edition.
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Thank You
For more ENT presentations, visit
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