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. 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. 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.
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.
7. 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
8. 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
9. Other Symptoms of NIHL
Tinnitus
Recruitment
Distortion of sounds (this may result in
poorer than expected word recognition
scores)
10. 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
11. Factors that exacerbate NIHL:
Simultaneous use of ototoxic drugs
Chemical exposure
Certain solvents used in industrial applications
Vibration
