NOISE-INDUCED HEARING LOSS Dr. Supreet Singh Nayyar, AFMC For more presentations, visit 14-Jul-12.

NOISE-INDUCED HEARING LOSS

Dr. Supreet Singh Nayyar, AFMC

For more presentations, visit www.nayyarENT.com

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http://www.nayyarent.com/

LAYOUT

• 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


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


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


General Aim Of A Noise Assessment

• Identify �• Obtain information �• Effectiveness of measures taken �• Choose appropriate personal hearing protectors�• Define hearing protection areas at work�


Excessive Noise

• 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


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


Auditory Effects Of Noise

• Auditory adaptation• Noise induced temporary threshold shift

(NITTS)• Noise induced Permanent threshold shift

(NIPTS)• Acoustic trauma


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.


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


Noise Induced Temporary Threshold Shift (NITTS)

• 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


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


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.


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


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


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



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


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


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


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


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


Mechanisms for NIHL - theories :

• Mechanical/structural damage, ranging from disturbance of the delicate stereocilia to tearing of the organ of corti and eventually permanent hair-cell loss, caused by severe motion of basilar membrane due to excessive noise



• 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



• 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


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


Audiometric configuration- acoustic notch

27

AUDIOGRAM

-100

102030405060708090

100110120

125 250 500 1000 2000 4000 8000

Test Frequency

Hearin

g T

hresh

old

(d

B)


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


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


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


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


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


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


Typical noise levels from firearmsOutdoor 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)


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


Prevention

• Noise hazard identification• Engineering controls• Personal hearing protection• Monitoring audiology• Record keeping• Health education• Enforcement • Programme evaluation


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


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. 2-5 kHz)

• Earmuffs attenuate the noise by 30 to 40 db.


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


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


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


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:– 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�



Permitted hours of exposure at work place

Hrs permitted Leq LOSHA

168421

0.50.25

87 dB90 db93 dB96 dB99 dB102 dB105 dB

85 dB90 dB95 dB100 dB105 dB110 dB115 dB


Ambient Noise standards and Guidelines in India

Area code

Category of area Limits in dB(A) Leq

Day Night

ABCD

Industrial areaCommercial areaResidential areaSilence Zone

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 (E) dated 22-11-2000. 4414-Jul-12 www.nayyarENT.com

Noise standards for Domestic appliances and construction equipments in India

Category Noise limit

dB(A) Window air-conditioners 1 ton &

aboveAir coolers

RefrigeratorsDiesel generators foe domestic

purposesCompact rollers, front loaders,

concrete mixers, cranes, vibrators and saws

686046

85-9075

• 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 422 (E) dated 19 May 1993 4514-Jul-12 www.nayyarENT.com

Noise limits for vehicles in India

Type of vehicle NoiseLimits dB(A)

Two wheeler displacement up to 80 cm3Displacement more than 80 cm3 but less than 175 cm3Displacement more than 175 cm3Three wheelerDisplacement up to 175 cm3Displacement more than 175 cm3Passenger carPassenger or commercial vehicleGross weight up to 4 tonneGross vehicle weight more than 4 tonne but up to 12 tonneGross vehicle weight more than 12 tonne

757780 7780757780

82

• Noise limits for vehicles from Jan 2003 as notified under Environment (Protection) Rules, 1996, by GSR 742(E) dated 25 Sep 2000 4614-Jul-12 www.nayyarENT.com

Research on NIHL

• Hair cell regeneration• Genetic and molecular basis for NIHL• Protection from conditioning the cochlear-efferent

system• Antioxidant therapy for NIHL and acoustic trauma


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


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.


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


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


Antioxidant therapy for NIHL

• N-L-acetylcysteine • Acetyl-L-carnitine• Carbanathione• Glutathione ( GSH )• Allopurinol• GSH peroxidase


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


Role of the Otolaryngologist

• 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


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.



Thank You

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NOISE-INDUCED HEARING LOSS Dr. Supreet Singh Nayyar, AFMC For more presentations, visit 14-Jul-12.

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