1. NOISE-INDUCED HEARING LOSS
Dr. Supreet Singh Nayyar, AFMC
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14-Jul-12

2. 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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3. 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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4. 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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5. 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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6. General Aim Of A Noise Assessment
•Identify
•Obtain information
•Effectiveness of measures taken
•Choose appropriate personal hearing protectors
•Define hearing protection areas at work
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7. Excessive Noise A heavy truck is about 85 db,
A jet taking off is about 120 db.
Suction and drill during ear surgery dB.
MRI units 90 dB.
Peak sound level in entertainment clubs 140dB
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8. 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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9. Auditory Effects Of Noise
Auditory adaptation
Noise induced temporary threshold shift (NITTS)
Noise induced Permanent threshold shift (NIPTS)
Acoustic trauma
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10. 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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11. 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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12. 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
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13. 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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14. 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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15. 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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16. Duration Of Exposure
An average work place exposure of 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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17. 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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18. 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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19. 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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20. 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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21. 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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22. 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 dB
Amplified noise in powerful hearing aids
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23. 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
other theiries
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24. 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
other theiries
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25. 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
other theiries
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26. 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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27. Audiometric configuration- acoustic notch
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28. 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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29. 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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30. 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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31. 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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32. 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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33. 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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34. Typical noise levels from firearms
Outdoor range
pistol cal. 10 m to the side dB peak(C)
rifle cal m to the side 154 – 158dB peak(C)
rifle cal 5.56 ear level dB peak(C)
revolver cal ear level 149 – 153dB peak(C)
Indoor range
pistol cal approx. 1.5 m behind 145 – 147dB peak(C)
pistol 9 approx. 1.5 m behind dB peak(C)
12 gauge pump action shotgun 150 – 151dB peak(C)
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35. 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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36. Prevention Noise hazard identification Engineering controls
Personal hearing protection
Monitoring audiology
Record keeping
Health education
Enforcement
Programme evaluation
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37. 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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38. 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.
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39. 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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40. 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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41. 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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42. 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
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43. 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
110 dB
115 dB
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44. Ambient Noise standards and Guidelines in India
Area code
Category of area
Limits in dB(A) Leq
Day Night A B C D
Industrial area
Commercial area
Residential area
Silence Zone
Ambient noise standards published in Gazette of India no 643 dt , Succeeded by the Noise pollution (Regulation and control ) rules, 2000(Gazette of India, vide SOI 123(E) dated and subsequently amended vide SO 1046 (E) dated
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45. Window air-conditioners 1 ton & above Air coolers Refrigerators
Noise standards for Domestic appliances and construction equipments in India
Category
Noise limit dB(A)
Window air-conditioners 1 ton & above
Air coolers
Refrigerators
Diesel generators foe domestic purposes
Compact rollers, front loaders, concrete mixers, cranes, vibrators and saws 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 and subsequently amended by GSR 422 (E) dated 19 May 1993
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46. Noise limits for vehicles in India
Type of vehicle
NoiseLimits dB(A)
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
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 75 77 80 82
Noise limits for vehicles from Jan 2003 as notified under Environment (Protection) Rules, 1996, by GSR 742(E) dated 25 Sep 2000
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47. 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
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48. 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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49. 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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50. 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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51. 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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52. Antioxidant therapy for NIHL
N-L-acetylcysteine
Acetyl-L-carnitine
Carbanathione
Glutathione ( GSH )
Allopurinol
GSH peroxidase
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53. 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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54. 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
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55. 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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56. 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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57. Thank You For more ENT presentations, visit www.nayyarENT.com
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