Noise damage

• noise trauma is the most common preventable cause of sensorineural hearing loss (1)
• the noise source may be (1)
  • occupational
    • prolonged industrial exposure
  • recreational
    • loud music
  • accidental
    • blast injury
    • gunfire
• oocupational noise damage may be : (2)
  • occupational acoustic trauma
    • is a sudden change in hearing
    • is caused by a single exposure to a sudden loud sound
      • e.g. explosion
  • occupational noise-induced hearing loss
    • develops gradually over a long period of time
    • is caused by exposure to continuous or intermittent loud sound
• characteristics of occupational noise-induced hearing loss: (2)
  • always sensorineural
  • often accompanied by high-pitched tinnitus (1)
  • affects hair cellsof the inner ear
  • typically bilateral
  • high frequencies are affected first (1)
  • earliest change noticed on audiogram is
    • “notching” at 3000, 4000, or 6000 Hz, with recovery at 8000 Hz
    • precise location of the notch depends on:
      • the frequency of the damaging noise
      • the length of the ear canal (2)
  • rate of hearing loss
    • is highest during the first 10-15 years of exposure
    • reduces as the hearing threshold increases
      • but, age-related loss, accelerates over time
  • loss of hearing is not reversible
  • diagnosis
    • clinical
    • based on the history of noise exposure
• treatment
  • the condition cannot be treated - damaged hair cells do not recover
  • early detection is vital to improve prevention (2)
  • a 10 dB threshold shift from baseline in pure tone average at 2000, 3000, and 4000 Hz is an significant early sign of permanent hearing loss
• prevention (1)
  • needs aggressive use of noise protection
  • foam-insert earplugs
    • decreases noise exposure by 30 dB
• medico-legal
  • noise damage is an acknowledged industrial disease
  • can be compensated for under the 1975 Industrial Injuries Act in the UK
  • there is an exposure limit in industry of 90dB for an 8 hour shift

Reference:

(1) differential diagnosis and treatment of hearing loss, Jon E. Isaacson, American Family Physician

(2) noise-induced hearing loss, Copyright ©  American College of Occupational and Environmental Medicine