Noise-Induced Hearing Loss


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Noise-Induced Hearing Loss

  1. 1. Noise-Induced Hearing Loss Ozarks Technical Community College HIS 125
  2. 2. Noise-Induced Hearing Loss (NIHL) Next to presbycusis, NIHL is the secondmost common cause of acquired hearing loss  According to the National Institute for Occupational Safety and Health (NIOSH), NIHL is amongst the top ten work-related injuries  NIHL is technically a noise-induced permanent threshold shift (NIPTS) 
  3. 3. Two Types of NIPTS  Acoustic Trauma    Permanent hearing loss after a single noise exposure Most commonly due to impulse noise (i.e. firearms) Gradually-developing NIHL  Gradual hearing loss due to noise exposure over an extended period of time (months to years)
  4. 4. NIHL  Dependent on intensity, duration, and type of noise exposure   The greater the intensity of the noise, the less exposure time is required for damaging effects to occur Impulse noise has the potential to physically break the hair cells with the potential for little to no recovery, whereas a steady-state noise (i.e. humming factory noise) may temporarily stress the hair cells, which then recover after a period of rest.
  5. 5.  Loud noise results in damage to the cochlea   OHCs are the 1st to be effected, followed by the IHCs and eventually the nerve Results in a SNHL with a “noise notch” on the audiogram  Reduction in pure tone thresholds from 3 to 6 kHz, with recovery at 8 kHz
  6. 6. Why the notch at 4kHz? The pinna effect and natural ear canal resonance amplify sounds from 2-4 kHz  The acoustic reflex in the middle ear reduces the amount of energy ≤500 Hz that is transmitted to the cochlea  In humans, the frequency most damaged by loud noise is ~ one-half to one octave above the highest frequency contained in the noise 
  7. 7. Audiometric Variation  The noise-notch may occur at varying frequencies depending on:    The frequency content of the noise The size and shape of the individual’s ear canal With continued noise exposure and advancing age, the true noise notch will disappear and the low frequencies will begin to show hearing loss as well
  8. 8. Other Symptoms of NIHL Tinnitus  Recruitment  Distortion of sounds (this may result in poorer than expected word recognition scores) 
  9. 9. Individual Susceptibility Some ears are “tougher” than others and more resilient to the effects of loud noise  Factors that may influence susceptibility:      Middle ear function/acoustic reflex function Protective effects of the efferent system Prior conditioning noise exposure (a lesser noise exposure may help protect or condition the ear to a later, more significant noise exposure) Genetic predisposition Note: There is no way to predict individual susceptibility
  10. 10. Factors that exacerbate NIHL: Simultaneous use of ototoxic drugs  Chemical exposure    Certain solvents used in industrial applications Vibration