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Noise induced hearing
loss
Rachel Robinson
Senior Audiologist
Walton
Tinnitus support group
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Noise induced hearing loss
† What is it?
† What sounds cause it?
† What are the effects?
† What are the symptoms?
† Who is affected?
† What research is being done?
† How we can prevent it?
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What is it?
†
Everyday we experience sound, normally at a
safe level that does not affect our hearing
†
However some sounds can be harmful if they
are too loud or loud and lasting a long time
†
Sensitive structures in our ears can be
damaged: hair cells. These are sensory
structures which convert sound energy into
electrical energy. Once damaged these cells
cannot grow back
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Hair cells
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Damaged Hair cells
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Definition
† The term Noise induced hearing loss
(NIHL) refers to a reduction in auditory
acuity associated with noise exposure.
† It can be classified into 3 categories
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Classification of NIHL
† 1.Noise induced temporary threshold
shift
† 2.Noise induced permanent threshold
shift
† 3.Acoustic trauma:
a single exposure to an intense sound
leads to an immediate hearing loss (National institutes of health consensus)
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History
†
From the first use of metals hearing has been at risk.
Gunpowder discovered about 1300AD added to the problem.
As far back as 1713 Ramazzini reported workers who
hammered copper for a living had their ears injured and
recommended the use of hearing protectors
†
Admiral Lord Rooney apparently became deaf for 14 days
following the firing of 80 broadsides from his ship HMS
formidable 1782
†
Fosbroke in 1831 gave an accurate description of NIHL in
blacksmiths, coining it ‘blacksmith’s deafness’
Taken from Scott -Browns Otorlaryngology Adult audiology Vol 2 6th ed
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What sounds Cause NIHL
†Continuous or Intermittent
†Explosive or Impulsive
†Above 85dB long or repeated
exposure may cause NIHL
†Source of sound- Industry, military, Leisure
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How loud is it?
†
Humming of a fridge is 45dB,
† Normal conversation is approx 60dB,
† heavy city traffic can reach 85dB,
† Motorcycles, firecrackers and small arms can
emit sound of between 120-150dB
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What are the effects?
† Damage to the sensitive hair cells in the
inner ear
† Hearing loss which may be
accompanied by tinnitus
† May be a temporary threshold shift
† Temporary threshold shift may go on to
be permanent
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What are the symptoms?
†
Hearing loss
†
Characteristic notched audiometric
configuration maximal in the 3-6kHz region with
recovery at 8kHz ? Show eg of NIHL??
†
Individuals with coincident hearing loss of other
aetiology (e.g. age!) may not have a notch > the
absence of a notch does not exclude NIHL (and
vice versa) (Coles et al 2000)
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Examples of audiograms
Normal Audiogram
Possible NIHL
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High frequency HL
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Who is affected?
† There is a wide variation in individual susceptibility
(Henderson et
al 1999)
† A potential genetic basis has been considered and
experimental evidence from studies with mice has
implicated the Ahl gene (davis et al 2001)
† Possible other factors like include smoking
(Wild et al 2005)
diabetes and cardiovascular disease(Lonsbury-Martin et al 1998)
† The combination of exposure to ototoxic agents and
noise has been shown to be synergistic in animal
models.(Makite et al 2003) A similar situation has been proposed
in humans with regard to industrial solvents ( Prasher et al
2002)
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What research is being done
†
Gene therapy in the regrowth of hair cells
† Research in Oregon shows a Key gene Atoh1
can not only cause cells to develop into hair
cells but they also function a normal hair cells
† Possibilty of using antioxidants to help prevent
production of free radicals which can go on to
cause hair cell death
† Programmed cell death inhibitors
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How can we prevent it?
† Hearing conservation programmes
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Noise hazard identification
Engineering controls
Personal hearing protection
Monitoring audiometry
Record keeping
Health education
Enforcement
Programme evaluation
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References
†
Coles RRA, Lutman ME, Buffin JT. Guidelines on the diagnosis of noise induced
hearing loss for medicolegal purposes. Clinical Otolaryngology and Allied
Sciences. 2000;25:264-73
†
Davis RR, Newlander JK, Ling XB, Cortopassi GA, Krieg EF, Erway LC. Genetic
basis for susceptibility to noise induced hearing loss in mice. Hearing Research.
2001;155:82-90.
†
Wild DC, Brewster MJ, Banjerjee AR. Noise induced hearing loss is exacerbated
by long term smoking.ClinicalOtolaryngology. 2005;30:517-20.
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Lonsbury-Martin BL, Martin GK, Telischi FF. Noise induced hearing loss. In
Otolaryngology-Head and Neck Surgery, 3rd edn. Mosby: St Louis, 1998:3153-85.
†
Makitie AA, Pirvola U, Pyykko I, Sakakibara H, Riihimaki V, Ylikoski J. The
ototoxic interaction of styrene and noise. Hearing Research. 2003;179:9-20.
†
Prasher D, Morata T, Campo P, Fechter L, Johnson AC, Lund SP et al.
NoiseChem: A European Commission research project on the effects of noise and
industrial chemicals on hearing and balance. Noise and Health. 2002;4:41-8
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