Acoustic Trauma - Types, Causes, Symptoms, Diagnosis, and Treatment

Introduction:

Normally, the hearing mechanism occurs through the conversion of sound waves into electrical signals, and these electrical signals are transferred to the brain. Sound waves enter the outer ear canal and reach the eardrum, causing it to vibrate. The eardrum vibration transfers these sounds to the three tiny bones of the middle ear (malleus, incus, and stapes), which in turn transfer these sound vibrations to the cochlea (which appears as a snail-shaped shell with fluid) in the inner ear, causing the hair cells (present in the cochlea) to bend. The bending of these hair cells causes the production of electrical signals. These electrical signals are then transmitted to the brain by the auditory nerve (the nerve supply to the ear) to detect these signals as sounds. If the vibrations sent to the eardrum are too loud and powerful, it results in damage to the middle and inner ear, leading to acoustic trauma.

What Is the Prevalence of Acoustic Trauma?

The prevalence of acoustic trauma accounts for five percent of the general population.

What Are the Types of Acoustic Trauma?

Acoustic trauma is of two types:

• Acute Acoustic Trauma: It occurs due to a single exposure to sudden, powerful sounds (like blasts or gunshot sounds) near the ear. It can be reversed and treated by medicinal therapy within 24 hours. It gets resolved after some time.

• Chronic Acoustic Trauma: This occurs due to continuous exposure to loud sounds (like in people working in machinery industries or continuous use of earphones with high volume). It leads to hearing loss slowly and gradually, resulting in permanent noise-induced hearing loss.

What Are the Causes of Acoustic Trauma?

Acoustic trauma is due to loud noise near the ears, like:

• Gunshot noise near the ears.

• Blast or commercial explosion near the ears.

• Long-term exposure to heavy machinery sounds in industries.

• Head injury.

• Using earphones or headphones for a longer duration in loud sound.

• Noise from firecrackers.

What Are the Signs and Symptoms of Acoustic Trauma?

The signs and symptoms related to acoustic trauma are:

• Ringing sensation in the ear (tinnitus).

• Pain in the ears.

• Partial or complete hearing impairment.

• Sudden deafness.

• Inability to distinguish between different sound pitches.

• Loss of balance.

• Dizziness.

• Pressure changes in the ears.

• Headaches.

• Bleeding from the ears (due to damage to the eardrum).

What Are the Diagnostic Methods for Acoustic Trauma?

Various diagnostic tests performed to rule out acoustic trauma include:

• History and Clinical Examination: The history of the patient for any recent exposures to loud sounds, frequency, and duration of exposure to the intense sounds of earphones, heavy motors, or machinery should be recorded. Ear examination is done by an ENT (ear, nose, and throat) specialist using a small instrument with light (otoscope) to detect damage to the eardrum.

• Pure Tone Audiometry (PTA) Test: This test helps to determine the severity, degree, and type of hearing impairment. It is done by placing a mini speaker in the ears and producing sound at different intensities in one ear at a time.

• Auditory Brainstem Response (ABR) Test: It is a painless test done to rule out any defects in the hearing pathway. In this test, electrodes are attached to the scalp and near the ears, and sound is produced by a mini speaker. The electrical impulse generated by the auditory-neural pathway (hearing or auditory pathway) in response to the sounds is evaluated.

• Computed Tomography (CT) Scans: This scan is done for the temporal area (lateral part of the skull) of the skull bone. It helps to rule out any defects present in the inner, middle, and outer ear.

• Tympanometry: This test is used to check the function or movement of the eardrum and the middle ear in response to the air pressure changes produced in the ear with the help of a small probe (tympanometer), and the results are recorded on the graph (tympanogram) which is then assessed.

What Is the Treatment of Acoustic Trauma?

Treatment methods for acoustic trauma are:

1. Medicinal Therapy: Drugs like steroids (Prednisolone - 1 to 2 mg/kg/day for seven days) are prescribed by the doctor for acute (first 24 hours of trauma) acoustic trauma. Steroids can be given either as intratympanic injections (within the tympanic membrane) or orally. Intratympanic steroid injections reduce inflammation or swelling and preserve hearing.

2. Hyperbaric Oxygen Therapy (HBOT): Hyperbaric oxygen therapy promotes oxygenation of the cochlea (which appears as a snail-shaped shell with fluid), reduces swelling within the inner ear, and minimizes cochlear damage.

3. Hearing Aids: Hearing aids like bone-anchored hearing implants (prosthesis placed surgically in the bone near ears) or other assistive listening devices are recommended by the doctor in cases of permanent hearing loss.

4. Eardrum Repair: Eardrum repair surgery (tympanoplasty) is done by an ENT (ear, nose, and throat) specialist in cases of perforated eardrums from acute acoustic trauma. Eardrum repair is done by using graft material like gelatin, fat, or other tissue graft to close the perforation.

What Are the Complications Associated With Acoustic Trauma?

1. Potential complications include progressive hearing loss, which is the primary concern with acoustic trauma.

2. There is also a possibility of experiencing tinnitus, characterized by ear ringing.

If symptoms of acoustic trauma are present, or if hearing loss occurs or worsens, consult a healthcare professional immediately.

What Is the Prognosis for Acoustic Trauma?

Hearing loss in the affected ear could be permanent. Using ear protection in noisy environments might help prevent further deterioration of hearing.

How Can Acoustic Trauma Be Prevented?

Acoustic trauma can be prevented by the following measures:

• Avoid using earphones for a longer duration.

• Protect your ears from loud noises, like in machinery industry, by using ear plugs or earmuffs.

In the event of a single exposure to intense sounds (gunshot sounds), report it to the doctor immediately for necessary treatment.

Conclusion:

Acoustic trauma occurs due to exposure to loud sound waves near the ears, which can damage the eardrum. Some of the acute acoustic trauma due to one-time exposure to intense sound (like gunshot sound near the ear) can be reversed by steroid therapy, which minimizes the risk of hearing loss and reduces the swelling in the ear. But in some cases, like continuous exposure to loud noise (use of earphones at high volume), acoustic trauma induces permanent noise-induced hearing loss, which can just be treated using hearing aids or other assisted listening devices but cannot be cured. Early diagnosis and management of acoustic trauma minimizes the risk of damage to the inner or middle ear and thus can prevent hearing loss.