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Noise induced hearing loss

Rachel RobinsonSenior AudiologistWalton

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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 IntermittentExplosive or ImpulsiveAbove 85dB long or repeated exposure may cause NIHLSource 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 earHearing loss which may be accompanied by tinnitusMay be a temporary threshold shiftTemporary 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 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 cellsPossibilty of using antioxidants to help prevent production of free radicals which can go on to cause hair cell deathProgrammed cell death inhibitors

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How can we prevent it?

Hearing conservation programmesNoise hazard identificationEngineering controlsPersonal hearing protectionMonitoring audiometryRecord keepingHealth educationEnforcementProgramme 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.

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