eMedicine Specialties > Otolaryngology and Facial Plastic Surgery > Inner Ear

Inner Ear, Noise-Induced Hearing Loss: Follow-up

Author: Neeraj N Mathur, MBBS, MS, Professor, Department of Ear, Nose and Throat, Lady Hardinge Medical College and Associated Smt SK and Kalawati, Saran Children's Hospital, University of Delhi, India; Professor and Head, Department of Ear, Nose and Throat, BP Koirala Institute of Health Sciences, Nepal
Coauthor(s): Peter S Roland, MD, Professor, Department of Neurological Surgery, Professor and Chairman, Department of Otolaryngology-Head and Neck Surgery, Director of Clinical Center for Auditory, Vestibular and Facial Nerve Disorders, Chief of Pediatric Otology, University of Texas Southwestern Medical Center; Adjunct Professor of Communicative Disorders, University of Texas School of Human Development
Contributor Information and Disclosures

Updated: Jul 16, 2009

Follow-up

Deterrence/Prevention

  • Oxidative stress plays a substantial role in the genesis of noise-induced cochlear injury that causes permanent hearing loss.
  • In adults with healthy audiograms, ear vulnerability to noise can be elicited and predicted by the use of objective DPOAE measurements. DPOAEs rely on the contractile properties of the outer hair cells. In response to tonal sound stimuli, these cells can generate retrograde wave sounds, the intensity of which can be captured and recorded by a very sensitive probe microphone in the external auditory canal. Any subclinical dysfunction of the middle ear or cochlea outer hair cells could slightly reduce DPOAEs and could influence the hearing performance in individuals exposed to noise and thus finding reduced DPOAEs in individuals with otherwise healthy pure-tone audiograms could be used in identifying them for their increased vulnerability to noise-induced hearing loss.12
  • In chinchillas, noise-induced cochlear oxidative stress (NICOS) can be reduced by the following means:
    • Acetyl-L-carnitine (ALCAR) is an endogenous mitochondrial membrane compound that helps maintain mitochondrial bioenergetics and biogenesis in the face of oxidative stress.
    • Carbamathione is a glutamate antagonist.
    • D-methionine (MET) can enhance cellular reduced glutathione (GSH) levels (ie, improve cochlear GSH deficiency state).
  • MET’s otoprotective action has a documented role, in a variety of species, against a variety of ototoxic insults including cisplatin-, carboplatin-, aminoglycoside- and noise-induced auditory threshold elevations and cochlear hair cell loss. Also MET can rescue individuals from permanent noise-induced hearing loss when MET is initiated 1 h after noise exposure.13
  • The studies reveal the potential for the use of NAC in a clinical population exposed to noise.14 However, as seen experimentally in chinchillas, l-NAC treatments (N -acetyl-l-cysteine) designed to reduce or prevent NIHL has a limited effectiveness. Long-duration exposures at levels that lead to PTS in excess of 50 dB or more with severe loss of OHCs and IHCs in the basal half of the cochlea may lead to the chronic production of excessively high levels of ROS or other free radicals that not only overwhelm the cells endogenous defense mechanisms but also the ability of antioxidant drugs to combat the ROS assault.15
  • In an animal study on guinea pigs, alpha tocopherol has been found to significantly decrease noise-induced auditory brainstem response threshold shifts and attenuate noise-induced outer hair cell stereocilia loss. This also supports the notion that reactive oxygen species (ROS) is involved in metabolic damage of the organ of Corti.
  • In a study of guinea pigs, direct infusion of dexamethasone into the perilymphatic space was observed to have a protective effect against noise-induced trauma.
  • Deterrence is the only accepted management method for NIHL. OSHA requires hearing conservation programs if noise exposures in the workplace exceed 85 dBA. The Walsh-Haley noise standard requires that engineering or administrative controls be used to ensure that noise levels do not exceed the PEL. If noise levels cannot be brought down to the PEL, hearing protection must be provided. Its use must be enforced.
  • Noise levels must be monitored, either with area monitoring or personal dosimetry. Personal dosimetry is required if workers are exposed to variable noise levels.
  • Noise levels must be posted in work areas.
  • The following features are essential for an adequate hearing conservation program:
    • Hearing conservation programs must include a baseline audiometry performed within 6 months of onset of exposure for all employees. The audiogram must be obtained when the employee has not been exposed to hazardous noise for at least 14 hours.
    • Annual audiometric testing should be performed for workers whose TWAs equal or exceed 85 dBA.
    • Workers exposed to TWA of 85 dBA or higher are required to have annual training about the effects of noise on hearing and the purpose of audiometric testing and hearing protective devices (HPDs).
    • A large number of additional recording and reporting requirements are included in OSHA regulations.
  • If exposure to loud environmental noises cannot be avoided, hearing protection should be used. Unfortunately, enforcement has been sporadic. HPDs vary considerably in their effectiveness, comfort, and cost. The following information should be taken into consideration when considering HPDs:
  • Only devices that are designed for hearing protection and tested for efficacy should be used. Items such as cotton, tissue paper, and expended cartridge casings provide no meaningful noise attenuation.
  • Earplugs are available with attenuation levels from as low as 10 dB to as high as 32 dB. They can be purchased over the counter or custom made. Earplugs can be as effective as earmuffs. However, earplugs are effective only when properly inserted. When earplugs are improperly inserted, noise attenuation may be eliminated or greatly reduced. Earplugs are especially useful when noise exposure is continuously sustained.
  • Earmuffs can provide as much attenuation as can earplugs. An advantage of earmuffs is that they are easy to correctly place: whether they are properly inserted or installed is not an issue. Earmuffs are especially useful when exposure to noise is relatively intermittent. Runway workers may need to put on and take off earmuffs many dozens of times a shift. These workers would not likely put earplugs in and out that frequently; if they did, many of those installations would probably be imperfect.
  • Earmuffs that permit normal hearing in the absence of a loud noise are now available. The muffs are able to detect the presence of a loud noise and attenuate it before it reaches the human ear. These devices have achieved a much higher level of acceptability among sports shooters because they permit normal hearing except when a firearm is discharged. Sports shooters often worry that their efficiency is impaired if they cannot hear environmental sounds and that their safety is imperiled if they cannot understand what others around them are saying.
  • The most effective ear protection is the ear protection the person is willing to wear.

Prognosis

  • TTS are reversible, but PTSs are not. No method of treatment is available, and no recovery is expected once a PTS has occurred.
  • However, hearing loss should not progress if exposure to the injurious noise is eliminated. Moreover, as the severity of the hearing loss increases, the rate of progression decreases, provided the injurious stimulus remains constant.

Patient Education

For excellent patient education resources, visit eMedicine's Ear, Nose, and Throat Center. Also, see eMedicine's patient education article Hearing Loss and Tinnitus.

Miscellaneous

Medicolegal Pitfalls

  • Noise-induced hearing loss (NIHL) frequently becomes a medicolegal issue. A large body of law surrounds the issue of disability secondary to NIHL.
  • Workers' compensation claims are frequent in the area of NIHL, and both federal and state laws govern compensation claims. These laws are not uniform.
  • The committee on hearing and equilibrium of the American Academy of Otolaryngology has established a computational method to determine hearing handicap. It recognizes that hearing thresholds of 500, 1000, 2000, and 3000 Hz are critical for understanding human conversation, and it uses only those frequencies in the calculation of hearing handicap. The method also recognizes that overall hearing acuity is disproportionately determined by the acuity of the better-hearing ear. Consequently, the calculation heavily favors the better-hearing over the poorer-hearing ear. The method recognizes a 25-dB threshold or better to be normal. The computation is performed as follows:
    • Compute the sum of the hearing threshold levels at 500, 1000, 2000, and 3000 Hz and divide by 4. Subtract 25 from the average. Multiply the result by 1.5 to produce the percent monaural hearing impairment.
    • If the monaural percent figure is the same for both ears, that figure expresses the percent handicap. If the percent monaural hearing impairment is different between ears, apply the formula (5 x % of better ear) + (1 x % poorer ear) divided by 6 = percent hearing handicap.
  • The AMA's Guides to the Evaluation of Permanent Impairment provides tables that can convert percent binaural handicap into "percent disability of the whole person."
  • Most individuals have hearing loss that has arisen from several causes. Hearing loss due to presbycusis is eventually present in most individuals. Occasionally, a physician is asked to allocate the percent of hearing loss due to noise exposure as distinct from the percent due to other causes. Age correction of audiograms is possible and can be used help allocate or attribute the proportion of hearing loss due to noise-induced PTS. However, age correction of audiograms is not generally considered appropriate for compensation assessment purposes.
  • Diagnosis of NIHL should rarely be made on the basis of the audiometric pattern alone. Information about the level of noise exposure should be a part of the diagnosis whenever possible.
 


More on Inner Ear, Noise-Induced Hearing Loss

Overview: Inner Ear, Noise-Induced Hearing Loss
Differential Diagnoses & Workup: Inner Ear, Noise-Induced Hearing Loss
Treatment & Medication: Inner Ear, Noise-Induced Hearing Loss
Follow-up: Inner Ear, Noise-Induced Hearing Loss
Multimedia: Inner Ear, Noise-Induced Hearing Loss
References
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Further Reading

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Keywords

hearing loss, noise-induced hearing loss, NIHL, non-occupational hearing loss, socioacusis, environmental noise, noise exposure, occupational hearing loss, occupational noise-induced hearing loss, ONIHL, acoustic trauma, workplace noise

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Contributor Information and Disclosures

Author

Neeraj N Mathur, MBBS, MS, Professor, Department of Ear, Nose and Throat, Lady Hardinge Medical College and Associated Smt SK and Kalawati, Saran Children's Hospital, University of Delhi, India; Professor and Head, Department of Ear, Nose and Throat, BP Koirala Institute of Health Sciences, Nepal
Neeraj N Mathur, MBBS, MS is a member of the following medical societies: Association of Otolaryngologists of India, Cochlear Implant Group of India, Indian Medical Association, National Academy of Medical Sciences, India, Neuro-Otologic and Equlibriometric Society of India, and Royal Society of Medicine
Disclosure: Nothing to disclose.

Coauthor(s)

Peter S Roland, MD, Professor, Department of Neurological Surgery, Professor and Chairman, Department of Otolaryngology-Head and Neck Surgery, Director of Clinical Center for Auditory, Vestibular and Facial Nerve Disorders, Chief of Pediatric Otology, University of Texas Southwestern Medical Center; Adjunct Professor of Communicative Disorders, University of Texas School of Human Development
Peter S Roland, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Otolaryngic Allergy, American Academy of Otolaryngology-Head and Neck Surgery, American Auditory Society, American Laryngological Rhinological and Otological Society, American Neurotology Society, American Otological Society, North American Skull Base Society, and Society of University Otolaryngologists-Head and Neck Surgeons
Disclosure: Alcon labs Honoraria Speaking and teaching; GSK Honoraria Speaking and teaching; Advanced Bionics Honoraria Board membership; Cochlear corp Honoraria Board membership; Med El corp travel grants Consulting

Medical Editor

S Valentine Fernandes, MBBS, MCPS, FRCSEd, FRACS, FACS, Conjoint Senior Clinical Lecturer, Department of Otorhinolaryngology, Newcastle University; Senior Consultant Surgeon, Department of Otorhinolaryngology-Head and Neck Surgery, John Hunter, Toronto Private and Kurri Hospitals, Australia
S Valentine Fernandes, MBBS, MCPS, FRCSEd, FRACS, FACS is a member of the following medical societies: American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, and American College of Surgeons
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Gerard J Gianoli, MD, Clinical Associate Professor, Department of Otolaryngology-Head and Neck Surgery, Tulane University School of Medicine; Vice President, The Ear and Balance Institute; Chief Executive Officer, Ponchartrain Surgery Center
Gerard J Gianoli, MD is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery, American College of Surgeons, American Neurotology Society, American Otological Society, Society of University Otolaryngologists-Head and Neck Surgeons, and Triological Society
Disclosure: Nothing to disclose.

CME Editor

Christopher L Slack, MD, Otolaryngology-Facial Plastic Surgery, Private Practice, Associated Coastal ENT; Medical Director, Treasure Coast Sleep Disorders
Christopher L Slack, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, and American Medical Association
Disclosure: Nothing to disclose.

Chief Editor

Arlen D Meyers, MD, MBA, Professor, Department of Otolaryngology-Head and Neck Surgery, University of Colorado School of Medicine
Arlen D Meyers, MD, MBA is a member of the following medical societies: American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, and American Head and Neck Society
Disclosure: Covidien Corp Consulting fee Consulting; US Tobacco Corporation unstricted gift unknown; Axis Three Corporation Ownership interest Consulting; Omni Biosciences Ownership interest Consulting; Sentegra Ownership interest Board membership; Syndicom Ownership interest Consulting; Oxlo  Consulting; Medvoy Ownership interest Management position

 
 
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