Noise-Induced Hearing Loss

What is Noise-Induced Hearing Loss?

Noise-induced hearing loss is the reduction in the ability to hear that is caused by prolonged and continuous exposure to high noise levels. The hearing loss may be temporary in the beginning, but becomes permanent if measures are not taken to reduce the exposure to noise.

Noise-induced hearing loss can also be caused by a sudden loud sound such as a gunshot or airhorn.

Loud sounds of traffic, rock music and continuously listening through headphones or earphones can harm the receptor cells of the cochlea and cause hearing loss. The loss is usually at high frequencies which lead to impaired perception of speech.

Exposure to loud noise at work place, as in factories, can also be the cause of noise-induced hearing loss. Government standards regulate allowable exposure to noise and the corporate take preventive measures to protect the hearing of their employees.

What are the Types of Noise-Induced Hearing Loss?

Noise-induced hearing loss can be temporary or permanent. Threshold shift is the term used to mention the reduction in hearing sensitivity, particularly for the purposes of hearing loss due to exposure to loud noises.

When hearing loss that has occurred due to noise is restored after a period of rest of about two days, the condition is referred to as temporary threshold shift.

When the hearing loss due to noise exposure can never be recovered the condition is called permanent threshold shift.

The impairment of hearing caused by exposure to loud noise is sensorineural in nature. This means that the damage happens in the inner ear. There are millions of hair cells in the cochlea which send the sound signals to the auditory nerve. The auditory nerve carries these impulses to the brain which interprets as the sound stimulus.

The hair cells in the cochlea die on exposure to the noise and thus cause hearing loss.

What are the Causes of Noise-Induced Hearing Loss?

Noise-induced hearing loss can be caused by a sudden loud sound of more than 110 decibels that damages the cells of the inner ear. This can be:

• A gun-shot close to the ear
• An unusually loud firecracker
• A sudden loud sound via the loudspeakers
• A clap of thunder from a storm that occurs in close proximity

Gradual and continuous exposure to sound levels more than 90 decibels can initially cause a temporary threshold shift. If this is not noticed or rectified, the condition can progress to permanent threshold shift.

• Exposure to high levels of traffic noise
• Exposure to noise at work place due to loud work environment
• Listening to music continuously at high volumes

• Loud concerts and discos

Some of the occupations where noise levels are high and can cause damage to hearing sensitivity include:

• Construction
• Manufacturing
• Transporation
• Military
• Musicians (orchestra players and rock concerts)
• Mining

What are the Symptoms of Noise-Induced Hearing Loss?

Noise-induced hearing loss can occur without the presentation of any symptoms. If the person can recognize the diminished ability to hear, especially in a noisy background, further investigations and measures can help in preventing noise-induced hearing loss.

Some of the common symptoms of noise-induced hearing loss include:

• Reduced ability to understand speech, especially in a noisy background
• Tinnitus (ringing in the ears)
• Dizziness, if the vestibular part of the inner ear is affected
• Some pain in one or both ears

What Happens in the Ear When There is Noise-induced Hearing Loss?

The hair cells of the cochlea sway in response to the vibrations passed on by the three tiny bones of the inner ear. The nerve endings of the vestibulocochlear nerve are present in the hair cells. These nerve endings receive the swaying movement as electrical impulses and send them to the brain. The brain interprets the electrical impulses coming from the vestibulocochlear nerve as sound stimulus.

Various types of damage that can possibly occur due to overstimulation of the cochlea or nerve are as follows.

• Hair cells can bend too much or break in response to loud sound
• Inflammation of the hair cells and consequently poor blood supply
• Damages at the junctions of the nerves

How do you Diagnose Noise-Induced Hearing Loss?

Noise-induced hearing loss is usually diagnosed with a combination of history of exposure to noise levels and the results of a pure-tone audiometry.

Studies suggest that noise-induced hearing loss is generally observed to affect the higher frequencies of a person's hearing range. There is a typical "dip" in the audiogram between the frequencies of 3000 Hertz to 6000 Hertz.

How Do You Treat Noise-Induced Hearing Loss?

Sudden hearing loss has been known to respond to certain treatments and better recovery rates were noted in patients who received treatment within one hour of exposure.

Studies indicate the success of the following treatments for sudden hearing loss:

• Intratympanic (via ear drum) injection of a cell permeable ligand, AM-111.
• Use of antioxidants after an exposure to an unbearable loud sound

Currently, research does not indicate any reversal of the effects of permanent hearing loss that is caused by continuous exposure to loud sounds. Studies are being done to explore the possibility of replacing the damaged hair cells with regenerated cells. This can be done using the mechanism of gene transfer.

How do you Prevent Noise-Induced Hearing Loss?

The following are some tips to be followed to prevent noise-induced hearing loss.

• Avoid places where noise levels are very high. For example, rock concerts, high traffic noise, public speaker systems.
• Use personal noise reduction devices like ear plugs and ear muffs to protect your ears from loud sounds.
• When hearing via earphones or stereos, use lower volume levels.
• If workplace is noisy, use hearing conservation programs to preserve hearing.
• Educate yourself about the levels of dangerous noise levels.
• Tinnitus is a noise heard that seems to come from inside the ear. Do not ignore tinnitus and consult a doctor immediately.
• If you suspect hearing loss or are not able to understand speech in a noisy background, get your hearing tested.

Health Tips

• Stay away from loud sounds and noisy environments.
• Listen to music at lower volume levels.
• Never use any sharp object to "clean" your ears.
• Get any infection of the nose, throat or ear treated immediately.
• Do not ignore any kind of tinnitus or noise in the ear.

References:

1. What is Noise-Induced Hearing Loss - (http://hearinghealthfoundation.org/what-is-nihl)
2. Noise-Induced Hearing Loss (NIHL) - (http://dangerousdecibels.org/education/information-center/noise-induced-hearing-loss/)
3. Noise-Induced Hearing Loss - (http://american-hearing.org/disorders/noise-induced-hearing-loss/)
4. Information about Noise-Induced Hearing Loss - (https://en.wikipedia.org/wiki/Noise-induced_hearing_loss)

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