We all know that exposure to extremely loud noises, whether it’s an explosion, a firecracker or even a concert; can lead to a permanent hearing loss. Moreover knowing about how to provide treatment for noise-induced hearing loss, that affects nearly about 15 percent of American’s total population, has on a large scale remained a mystery.

A new research from the Keck School of Medicine of USC stated that on how noise-induced hearing loss happens and showed how a simple injection of a salt and sugar based solution into the middle ear helps in preserving hearing. The results of this study were published in PNAS.

Deafening Sound

The researchers first had to understand its mechanism, if they are looking for developing a treatment for noise-induced hearing loss. So, to help this out, they developed a tool using novel miniature optics to image inside the cochlea- the hearing portion of the inner ear. They later exposed mice to a loud noise that was much similar to that of a roadside bomb.
With this experiment, they came to know that two things happen after exposure to a loud noise-
1. The sensory hair cells, which are the cells that are responsible for sound detection and conversion of it to neural signals, die.
2. The inner portion of the ear fills with excess fluid that leads to the death of neurons.

“That buildup of fluid pressure in the inner ear is something you might notice if you go to a loud concert,” says the study’s corresponding author John Oghalai, MD, chair and professor of the USC Tina and Rick Caruso Department of Otolaryngology – Head and Neck Surgery and holder of the Leon J. Tiber and David S. Alpert Chair in Medicine. “When you leave the concert, your ears might feel full and you might have ringing in your ears. We were able to see that this buildup of fluid correlates with neuron loss.”

He stated that both the neurons and the sensory hair cells play critical roles in hearing.

Oghalai later stated that- “The death of sensory hair cells leads to hearing loss. But even if some sensory hair cells remain and still work, if they’re not connected to a neuron, then the brain won’t hear the sound,”

With the experiment, the researchers discovered that the sensory hair cell death occurred immediately after exposure to loud noise and that too it was irreversible. Neuron damage, however, had a delayed onset, opening a window of opportunity for treatment.

The Solution

The buildup of this fluid in the inner ear occurred over a period of a few hours after loud noise exposure and also it contained a higher concentration of potassium. For reversing the effects of the potassium and reduce the fluid buildup, through the eardrum, the salt- and sugar-based solutions were injected into the middle ear, just three hours after the noise exposure. The researchers came to a result that this treatment with these solutions prevented 45-64 percent of neuron loss- suggesting that the treatment may offer a way to preserve hearing function.

The treatment could have several potential applications, Oghalai explains.

“I can envision soldiers carrying a small bottle of this solution with them and using it to prevent hearing damage after exposure to blast pressure from a roadside bomb,” he says. “It might also have potential as a treatment for other diseases of the inner ear that are associated with fluid buildup, such as Meniere’s disease.”

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