Noise-Induced Inner Ear Nerve Damage Relates To Endolymphatic Hydrops, Study Finds

Exposure to loud noises, such as a firecracker or a breathtaking concert, is the most common preventable cause of hearing loss. Research suggests that 12% or more of the world’s population is at risk for noise-induced hearing loss.

Loud sounds can lead to loss of auditory nerve cells in the inner ear, which are responsible for sending acoustic information to the brain, causing hearing difficulties. However, the mechanism behind this hearing loss is not fully understood.

Now, a new study from USC’s Keck Medicine links this type of nerve damage in the inner ear to a condition known as endolymphatic hydrops, a buildup of fluid in the inner ear, showing that these two phenomena occur at levels of noise exposure that people might encounter in their daily lives. life.

Additionally, the researchers found that treating the resulting fluid buildup with readily available saline solution reduced nerve damage in the inner ear.

This research provides clues to better understand how and when noise damage to the ears occurs and suggests new ways to detect and prevent hearing loss. “

John Oghalai, MD, otolaryngologist at Keck Medicine, chair of the otolaryngology department at USC Caruso – Head and Neck Surgery and lead author of the study

A previous Oghalai study in mice exposed to blast pressure waves simulating a bomb explosion linked nerve damage to a buildup of fluid in the inner ear.

For this study, Oghalai and his colleagues wanted to explore the effect of loud current sounds ranging from 80 to 100 decibels on the ear. After the exposure, they used an imaging technique known as optical coherence tomography to measure the fluid level from the inner ear into the cochlea, the hollow, spiral-shaped bone found in the ear. internal.

Until exposure to 95 decibels of sound, the fluid level in the inner ear remained normal. However, the researchers found that after exposure to 100 decibels -; which is equivalent to sounds such as an electric lawn mower, chainsaw or motorbike -; the mice developed a buildup of fluid in the inner ear within hours. A week after this exposure, the animals lost auditory nerve cells.

However, when the researchers applied hypertonic saline, a salt-based solution used to treat nasal congestion in humans, to the affected ears one hour after exposure to noise, the immediate build-up of fluid and the Long-term nerve damage has diminished, implying that hearing loss could be at least partially prevented.

These study results have several important implications, according to Oghalai, especially since the loss of nerve cells in the inner ear is known as “hidden hearing loss” because hearing tests are unable to detect the damage. .

“First, if human ears exposed to loud noise, such as the deployment of a siren or an airbag, can be analyzed for a level of fluid buildup -; and this technology is already being tested -; healthcare professionals may have a way to diagnose an impending nerve. too bad, “he said.” Second, if the analysis found a buildup of fluid, people could be treated with hypertonic saline and possibly save their hearing. “

He also believes the study opens a new window into understanding Ménière’s disease, a disorder of the inner ear that causes dizziness, ringing in the ears (tinnitus) and hearing loss.

“Previously, it was believed that the accumulation of fluid in the inner ear was mainly related to Ménière’s disease. This study indicates that people exposed to loud noises experience similar changes, ”he said.

Oghalai hopes this study will lead to further research into why ear fluid buildup occurs and encourage the development of better treatments for Ménière’s disease.

The study was supported by the National Institute on Deafness and Other Communication Disorders.