Naomi Bramhall, AuD, PhD, Audiologist and Research Investigator at the National Center for Rehabilitative Auditory Research

PORTLAND, OR — It’s such a common ailment among veterans that it’s almost a given: If you served any time in the military, you’re walking out with some type of hearing problem. That usually presents as hearing loss or tinnitus—a persistent ringing sound in the ears.

Sometimes diagnosing it is as simple as conducting a hearing test. However, new research shows that there are forms of hearing loss that do not get picked up by those tests. Veterans recognize that something has changed, but physicians are unable to diagnostically prove it.

Naomi Bramhall, AuD, PhD, an audiologist and research investigator at the National Center for Rehabilitative Auditory Research (NCRAR) has made it her mission to find ways to diagnose—and hopefully eventually treat—these forms of hidden hearing loss.

Bramhall originally thought she wanted to study regeneration of the cells of the inner ear, but quickly felt like she’d moved too far away from her clinical background as an audiologist.

“I wanted to do work that was with people,” she said.

She learned about NCRAR, where she could do research while serving as a clinician at VA, and wrote a career development grant to investigate a new type of noise-induced hearing loss in veterans. Her grant was accepted, and she has been with NCRAR for the last decade.

“The research center where I was studying hair-cell regeneration had made a new discovery,” she explained. “We examined mice who were noise-exposed enough to cause temporary changes in their ability to detect sound, but not permanent. These mice had some permanent loss of the synaptic connections between the sensory cells and the auditory nerve fibers. There was a lot of concern that this might happen to humans, too.”

If so, it wouldn’t show up on the normal battery of hearing tests.

“We think the types of complaints that could stem from this [synaptic damage] are things like tinnitus … or difficulty understanding speech in noisy environments,” she said. “These are very common complaints in the veteran population.”

Bramhall’s early studies at NCRAR have since backed this up.

One study showed that young military veterans who have normal hearing had some differences on physiological metrics compared to nonveterans who had minimal noise exposure history. This suggested they might have this type of synaptic loss. Another study showed that veterans with tinnitus had some physiological differences to nonveterans.

This provided the first hard evidence that what those previous researchers had seen in mice was happening in humans, too.

“Right now we’re working on how to diagnose this in the clinic,” Bramhall explained. “We really can’t study possible treatments until we have a way of identifying individual patients.”

The first step is creating a baseline. What does the physiology of nonveterans with minimal noise exposure and no complaints of hearing problems look like?

“Eventually we’ll have normative ranges,” she said. “Once we have a way of determining if they’re likely to have this, we can look at treatments.”

That treatment will likely start with hearing aids. Audiologists sometimes prescribe hearing aids for patients complaining of not understanding speech in noisy environments, even when those complaints don’t always register as hearing loss on the usual tests.

“In that case, [the problem might be solved] if you can give them just a little bit of amplification,” Bramhall said.

However, there’s little data as to its effectiveness, especially in the private sector where hearing aids are expensive and insurance might not cover them without an official diagnosis of hearing loss.

“There’s also animal studies being done looking at drug treatment for this,” Bramhall said. “It looks like there are certain drug treatments that can be used to regenerate the synapses.”

The timeline for those drugs being administered to humans is a long one, though.

That applies to Bramhall’s research, as well. The current studies looking at normative ranges will take two to three years, after which she’ll start looking at hearing aid efficacy, which might take another three to four years. Drug treatments are likely at least a decade away.

In the meantime, Bramhall is making discoveries that could be applicable right now, including in what veterans understand about noise-induced hearing loss.

“One thing veterans don’t seem to understand is that there’s an interplay between how loud a sound is and how long you listen to it that determines risk,” she explained. “I ask them, ‘Do you use firearms?’ And they say, ‘Yeah, but I only fire off a couple shots.’ They assume, because the duration is really short, that it’s no big deal. But what they’re failing to understand is that the intensity level or loudness of a firearm is astronomical.”

Also, while veterans usually recognize when they’ve experienced some loss in hearing, the same isn’t true of newly acquired tinnitus.

“What I found surprising is how many people have tinnitus that think that everyone experiences it. That it’s normal,” Bramhall said.

As for the common complaint of not being able to understand conversations in loud environments, Bramhall is working on a way to better understand and measure that experience. In her study, she is recreating that environment and using infrared cameras to study patients’ pupil dilation—an indicator of cognitive effort.

“If you have to go out and have a conversation with somebody in a bar, for example, you may still be able to understand what they’re saying, but you may have to work a lot harder or expend a lot more cognitive effort than if you were having that conversation with them at home,” she explained. “You’re using cognitive resources to fill in blanks to understand what people are saying.”