By Capt. Edward Lundquist, USN (Ret)
The engines, aircraft, machinery, and weapons servicemembers regularly use and are around are loud, painfully loud. So it’s not surprising hearing injuries top the list of VA medical disability for all servicemembers. ( Here are some signs you might need hearing help.)
To protect servicemembers from potential hearing injuries caused by loud noises, the Office of Naval Research’s Noise-Induced Hearing Loss programis investigating technologies and approaches to prevent hearing damage and even restore hearing.
Susceptibility to hearing damage
The inner ear cochlear hair cells are exquisitely designed but can be damaged easily by noise, and they don’t grow back. According to program lead Kurt Yankaskas, a world-recognized expert in the field of military noise who has a background as a naval engineer and previously worked in undersea sound detection, research in the past two years has shown that during an auditory insult, nerve cells are damaged and withdraw or disconnect from the inner ear hair cells, resulting in a silent nervous system failure over time.
When the nerves are damaged, Yankaskas says it can result in the “cocktail party effect,” which he describes as an inability to discriminate the speaker in a room where multiple conversations are going on. ONR’s research investment in nerve regeneration and nerve cell connections is leading the field in many ways, including how to regenerate both hair and the nerve cells.
“We’ve been identifying new metabolic pathways and genetic markers that can help us anticipate who would be more susceptible to an auditory injury and how to protect them,” he says.
Studying susceptibility to hearing damage at the cellular level would help those individuals to take precautions. “If you have tender ears, you need to go into intense hearing conservation program, just as somebody with very fair skin needs to use SPF 50 sunscreen,” Yankaskas says.
While mammals can’t regenerate damaged cochlear hair cells, birds and amphibians can. During human fetal development, proteins are turning on and off the genetic assembly code, including the formulation of hearing apparatus. “It turns off when it’s done,” he says. “We’re sponsoring research at St. Jude Children’s Research Hospital to turn it back on again.”
By splicing DNA from a chicken into that of a mouse, researchers were able to show that damaged hearing apparatus could begin to regenerate. Though there’s much progress, results will not be immediate. “We were the first to demonstrate regeneration of hair cells in a live mouse,” Yankaskas says.
Yankaskas says researchers at Harvard University have identified 18 new genes in the past two years that have an effect on hearing. The genes determine what the cells do or don’t do. He says ONR is looking into pharmacological approaches and what compounds and combinations of compounds have a positive effect on those cells and perhaps help the body be more resilient in the event of an auditory assault.
St. Jude’s High-Throughput Screening Center is exploring novel drug treatments that might have an effect on the inner ear cells, taking advantage of the center’s library of a half million compounds covering the entire range of known chemicals. Hair cells are grown in the lab and then exposed to the different compounds to see which ones show promise for further study.
The hope is a precision-medicine approach can fine-tune the appropriate compounds to be prescribed for a specific individual.
To best treat patients, Yankaskas says a “personalized medicine” approach might identify a particular gene where the formation of a specific protein might indicate a vulnerability. “We want to learn how to counter the stress caused by an auditory injury,” Yankaskas says. “We’re trying to outwit Mother Nature, and it will take us years. But with every year that goes by, we unlock new clues.”
Prevention is key
For now, prevention still is the best medicine. The Navy has invited small businesses that offer protection from noise but enable the user to have situational awareness. This is especially important for people who work in dynamic and loud environments, such as on an aircraft carrier flight deck or in machinery spaces, and who need to be able to communicate with others and be aware of what’s happening around them in that same environment.
If you already suffer from hearing loss and are in need of a hearing aid, the DoD-sponsored Retiree At-Cost Hearing Aid Program might help with the costs. Learn more about the program.