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Noise induced trauma

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Noise is defined as unwanted or harmful sound that disrupts auditory comfort and poses risks to physiological and psychological health. Noise-induced hearing loss (NIHL) and acoustic trauma are significant, preventable health issues caused by exposure to excessive noise. These conditions are particularly prevalent in occupational settings, such as industries involving loud machinery, gunfire, or motor racing, as well as recreational activities like using personal music devices at high volumes. NIHL is a major occupational hazard, often leading to financial compensation claims for affected employees.

Types of Noise-Induced Hearing Loss

It can be categorized into two types based on exposure:

  1. Noise-Induced Hearing Loss (NIHL): It is caused by chronic exposure to excessive noise, typically in occupational settings. Depending upon the reversibility of the hearing loss is classified into two types:
    • Temporary Threshold Shift (TTS): There is temporary hearing loss that recovers within few days after noise exposure. It is caused by metabolic changes, such as reduced blood flow and cochlear hypoxia. Another hypothesis is there is bending of hair cells kinocilium due to sudden noise exposure.
    • Permanent Threshold Shift (PTS): There is permanent irreversible hearing loss caused by repeated or severe noise exposure. It results from structural damage, including:
      • Breakdown of actin filaments in stereocilia.
      • Swelling of inner ear structures.
      • Apoptosis and necrosis of outer and inner hair cells, the basilar membrane, and spiral ganglion cells.
  2. Acoustic Trauma (Sudden/Impulse Noise): It is caused by a single exposure to an extremely intense sound (e.g., explosions, gunfire, or firecrackers), reaching 140–170 dB SPL. It results in immediate hearing loss without a preceding temporary threshold shift (TTS). It can cause mechanical damage to the tympanic membrane, ossicles, organ of Corti, Reissner’s membrane, and hair cells, leading to permanent hearing impairment.

Factors Influencing Hearing Damage

  • Frequency of Noise: Sounds in the 2–3 kHz range are most damaging.
  • Intensity and Duration: Hearing damage is directly proportional to the intensity and duration of noise exposure.
    • Sounds below 80 dB(A) are generally safe.
    • Sounds above 130 dB(A) can cause immediate damage.
  • Continuous vs. Interrupted Noise: Continuous noise is more harmful than intermittent noise.
  • Individual Susceptibility: Genetic factors, pre-existing ear diseases, and systemic conditions (e.g., diabetes, cardiovascular disease) increase vulnerability.
  • Predisposing Factors: Smoking, blue eye colour, recreational drug use, and exposure to ototoxic agents.

Diagnosis

  1. History:
    • Patients present with bilateral sensorineural hearing loss (SNHL), often accompanied by tinnitus or hyperacusis.
    • A history of prolonged exposure to loud noise (occupational/recreational) is common.
    • In cases of acoustic trauma, unilateral hearing loss, otalgia, imbalance, and acute stress reactions may occur.
  2. Examination: Local ear examination may appear normal or show injury to the tympanic membrane and ossicles.
  3. Hearing tests:
    • Pure-Tone Audiometry (PTA): It is the gold standard test for diagnosis. There is a classic 4–6 kHz “notch” with preservation of lower and mid frequencies. The notch is symmetrical in both ears, with some recovery at 8 kHz. The notch deepens as noise exposure increases. However, all audiograms showing a notch at 4000 Hz are not due to noise-induced hearing loss and not all noise induced hearing loss present the typical 4000 Hz notch. 
    • Tympanometry: Normal middle ear function (unless tympanic membrane/ossicles are damaged).
    • Speech Audiometry: Assesses functional hearing loss.
    • Advanced Tests:
      • Otoacoustic Emissions (OAEs): Evaluates OHC function.
      • Auditory Brainstem Response (ABR): Rules out retrocochlear pathology (e.g., acoustic neuroma).
    • Additional Tests:
      • SISI Test: Helps detect cochlear pathology and rule out malingering.
      • Tympanometry (acoustic reflex).
      • Tone Decay Test.

        Noise induced trauma
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Why the 4 kHz Dip?

The anatomical location of the 4 kHz area of the basilar membrane corresponds to that area of basal turn (of the cochlea). It is more susceptible to damage due to:

  • The anatomical rigidity makes it prone to torsion and vascular injuries.
  • Reflex contraction of intratympanic muscles in response to loud sounds shifts the sound towards higher frequencies.
  • Increased resonance of the external auditory canal at this frequency.

Differential Diagnosis

  • Presbycusis(age-related hearing loss).
  • Ototoxic Drug-Induced Hearing Loss.
  • Meniere’s Disease.
  • Acoustic Neuroma.
  • Malingering(exaggeration of symptoms).

Preventive Measures

A. Prevention

  1. For Industrial Workers:
    • Pre-Employment and Annual Audiograms: For early detection of hearing loss.
    • Noise Regulation: Limit noise exposure to ≤115 dB (continuous/intermittent) and avoid impulse noise >140 dB.
    • Training Programs: Educate workers on NIHL risks and prevention.
    • Hearing Protection Devices:
      • Earplugs: Attenuate 15–30 dB (optimal for 3–5 kHz).
      • Earmuffs: Provide 30–40 dB attenuation (effective across 500 Hz–8 kHz).
      • Combined Use: Earplugs + earmuffs offer >40 dB protection.
      • Active Noise Reduction: Electronic devices that cancel out ambient noise, especially effective for low-frequency sounds (e.g., in aircraft).
    • Job Rotation: Shift workers to non-noisy areas periodically.
  2. For Personal Noise Trauma Prevention:
    • Volume Control: Keep music player volume low (≤60% of maximum volume for ≤60 minutes/day at ≤60 dB).
    • Headphone Choice: Use noise-cancelling, muff-type headphones instead of earbuds.
    • Regular Breaks: Take breaks from headphone use to allow ear recovery.
    • Early Consultation: Seek ENT advice if tinnitus or hearing loss occurs.

B. Legislation and Permissible Noise Levels

  1. Ministry of Labour, Govt. of India, Model rules under Factories Act: 
    • Permissible Exposure Limit (PEL): 90 dB(A) for 8 hours/day (5 dB rule of time-intensity states that “any rise of 5 dB noise level will reduce the permitted noise exposure time to half.).
    • Impulse Noise: No exposure above 115 dB(A)or impulse noise above 140 dB(A) is allowed.
  2. Noise Pollution (Regulation and Control) Rules 2000: The Ministry of Environment and Forest, Govt. of India has defined permissible limits of noise for various zones or areas. According to which silence zone is 100 m around the premises of hospitals, nursing homes, educational institutions and courts. Loudspeakers are prohibited between 10:00 PM and 6:00 AM.
  3. Environment Protection Rules 2006: Manufacture, sale and use of firecrackers generating sound levels above 125 dB (AI) or 145 dB (C) pk from 4 m distance from the point of bursting are not permitted. [dB (AI) = A-weighted impulse sound pressure level in decibels; dB (C) pk = C-weighted peak sound pressure in decibels].
  4. Permissible Noise Levels (Central Pollution Control Board, India):
    • Industrial Areas: 75 dB (day), 70 dB (night).
    • Residential Areas: 55 dB (day), 45 dB (night).
    • Commercial Areas: 65 dB (day), 55 dB (night).
  1.  

Permitted daily exposure (h)

Treatment

  1. Hearing Protection: Further noise exposure should be minimized using ear protection devices in the form of earplugs or earmuffs. It reduces the further risk of NIHL.
  2. Hearing Aids: Beneficial for managing severe, permanent hearing loss, though they cannot restore lost hearing. Cochlear Implants are used for profound hearing loss unresponsive to hearing aids.
  3. Medical management: Combined use of prednisolone and piracetam (nootropics) may help recover hearing after sudden noise exposure.
  4. Tinnitus Management:
    • Tinnitus Retraining Therapy (TRT): Combines cognitive counselling and sound therapy.
    • Improvement seen in 60–70% of patients.
  5. Hyperacusis Management: Similar to tinnitus, using sound therapy and counselling.
  6. Acoustic Shock: Requires psychological treatment.

Nonauditory Effects of Noise

  • Sleep disturbances lead to chronic fatigue and stress.
  • Hypertension and tachycardia
  • Annoyance and irritability.
  • Decreased performance at work and memory loss.
  • Mood disturbances and behavioural changes

Other important terminologies

  1. Early Onset Presbycusis: It is premature age-related hearing loss, typically occurring earlier than expected due to cumulative noise exposure from childhood. Chronic exposure to loud sounds can damage the cochlea, leading to early degeneration of hair cells and auditory structures.
  2. Socioacusis (Non-Occupational Noise-Induced Hearing Loss):  Hearing loss caused by non-occupational noise exposure, often from recreational or lifestyle activities.
    • Common Sources:
      • Loud Music: Concerts, music shows, and personal entertainment devices (e.g., headphones, earbuds) played at high volumes.
      • Open Vehicles: Motorcycles, snowmobiles, all-terrain vehicles (ATVs), and formula one racing cars.
    • Clinical Findings:
      • High-Frequency SNHL: Audiometric testing reveals a characteristic dip at 4–6 kHz.
      • Tinnitus: Often accompanies hearing loss.
      • Hyperacusis: Increased sensitivity to certain sound frequencies.

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Download the full PDF Link:

Noise Induced Trauma Best Lecture Notes Dr Rahul Bagla ENT Textbook

Reference Textbooks.

  • Scott-Brown, Textbook of Otorhinolaryngology-Head and Neck Surgery.
  • Glasscock-Shambaugh, Textbook of Surgery of the Ear.
  • P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
  • Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
  • Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck Surgery
  • Hans Behrbohm, Textbook of Ear, Nose, and Throat Diseases With Head and Neck Surgery.
  • Salah Mansour, Middle Ear Diseases – Advances in Diagnosis and Management.
  • Logan Turner, Textbook of Diseases of The Nose, Throat and Ear Head And Neck Surgery.
  • Rob and smith, Textbook of Operative surgery.
  • Anirban Biswas, Textbook of Clinical Audio-vestibulometry.
  • Arnold, U. Ganzer, Textbook of  Otorhinolaryngology, Head and Neck Surgery.

Author:

Dr. Rahul Bagla ENT Textbook

Dr. Rahul Bagla
MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi)
Fellow Rhinoplasty & Facial Plastic Surgery.
Renowned Teaching Faculty
Mail: msrahulbagla@gmail.com
India

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