Hidden Hearing Loss

New drug may prevent hearing loss after noise exposure

By Daniel Fink, MD, Chair, The Quiet Coalition

For many years, a body of research has shown that chemicals with antioxidant properties might prevent or reduce hearing loss after noise exposure. In animals, noise exposure reduces levels of a chemical called glutathione peroxidase 1 (a naturally occurring enzyme). A recent report in the British journal The Lancet looks at how a similar chemical, ebselen, works in helping to reduce “both temporary and permanent noise-induced hearing loss in preclinical studies.”

It appears to work quite well.

Of course, we at The Quiet Coalition think it’s better just to avoid loud noise exposure, which is 100% safe and effective at preventing hearing loss. That said, the experimental protocol raises interesting questions about research ethics. Namely, the study tested the efficacy of different doses of ebselen after the subjects, healthy adults aged 18–31 years, were exposed to loud sound. The measure of ebselen’s success was the prevention of a phenomenon called temporary threshold shift (TTS), more completely noise-induced temporary threshold shift (NITTS). This audiometric measure has been used for decades to measure the impact of noise on humans.

Unfortunately, recent research, beginning with a 2009 report and updated last year describes a phenomenon called “hidden hearing loss,” a synaptopathy (injury to the synapses in the cochlea) caused by noise exposure. Hidden hearing loss is called that because it is not detected by standard audiometric techniques. Hidden hearing loss is the likely cause of being unable to follow one conversation among many in a noisy environment, or having a normal or near-normal audiogram but still having difficulty understanding speech.

Many experts think that there is no temporary auditory damage. That is, TTS is a real phenomenon but the use of the word “temporary” is misleading because if TTS occurs then it is likely that permanent auditory damage has also occurred.

In this study, healthy young adults were exposed to noise levels loud enough and long enough to cause TTS, likely indicating permanent auditory damage. Some of the subjects were given large enough doses of the experimental drug ebselen to prevent TTS from occurring, but whether the drug would or wouldn’t work, and at what dosage, wasn’t known when the study began. Simply put, the study exposed all subjects to the threat of auditory damage, and most likely caused auditory damage in the subjects who received the placebo or didn’t get a high enough dose of the experimental drug.

All research protocols in the U.S. must pass review by an Institutional Review Board (IRB) which must make certain that steps are taken to prevent harm to research subjects.. Under the Helsinki Declaration of the World Medical Association, and in the United States under what is called the federal “Common Rule” (45 CFR §46 et seq.), human subjects must be protected. If there is a risk of permanent auditory damage when the phenomenon of TTS is observed–and Drs. Liberman and colleagues certainly think that temporary auditory changes denote permanent auditory damage–we think the IRB should have done more to protect the subjects from any possibility of harm.

How could a study that exposes young people to noise levels loud and long enough to cause TTS pass IRB review? We hope the federal Office for Human Research Protections will let us know.

Dr. Daniel Fink is a leading noise activist based in the Los Angeles area. He serves on the board of the American Tinnitus Association, is the interim chair of Quiet Communities’s Health Advisory Council, and is the founding chair of The Quiet Coalition, an organization of science, health, and legal professionals concerned about the impacts of noise on health, environment, learning, productivity, and quality of life in America.

New explanation for why older people can’t hear in noisy environments

Photo credit: Filipe Fortes licensed under CC BY-SA 2.0

By Daniel Fink, MD, Chair, The Quiet Coalition

There are already several explanations about why middle-aged and older people can’t understand speech in noisy environments. One may just be high-frequency hearing loss caused by noise, which makes it hard to hear the higher-pitched consonant sounds (F, S, SH, T, V) that allow us to differentiate similar sounding words (Fear, Sear, Shear, Tear, Veer). (See the graph in this CDC Vital Signs Issue.) Another reason may be a phenomenon called “hidden hearing loss,” which is caused by noise damage to nerve junctions (synapses) in the inner ear.

And now a new report indicates that there may also be a brain or central processing problem. A study conducted at the Max Planck Institute in Germany, “analyzed what happens in the brain when older adults have trouble listening in loud environments.”  The researchers “monitored the brains of 20 younger adults ages 18 to 31, and 20 older adults in their 60s and 70s, during a listening task” in which constant background noise was played while participants were told to focus on certain targeted sounds.

What the researchers found was that “the younger adults were able to zero in on the target signals while filtering out the irrelevant noise,” but the older participants had “a harder time tuning out the background noise.” What remained unclear was whether the “degradation of the ear’s ability to hear actually leads to a decline in the brain’s ability to filter out noise and hear a single sound,” or whether “the brain’s listening ability erodes independently of any changes going on in the ear.”

As for why older people have a difficult time understanding speech in noisy environments, it most likely is that all three factors occur to varying degrees in various individuals. But one thing is certain, preventing hearing loss is simple: avoid loud noise. And improving the ability of people young and old to follow conversations is also simple: turn down the volume in indoor places.

Link via the UK Noise Association.

Dr. Daniel Fink is a leading noise activist based in the Los Angeles area. He serves on the board of the American Tinnitus Association, is the interim chair of Quiet Communities’s Health Advisory Council, and is the founding chair of The Quiet Coalition, an organization of science, health, and legal professionals concerned about the impacts of noise on health, environment, learning, productivity, and quality of life in America.

 

Revisiting the routine audiological test

By Daniel Fink, MD, Chair, The Quiet Coalition

An audiology examination involves examination of the ear to inspect the ear drum, and then tests based on the patient’s complaints. Routine audiology testing includes pure tone audiometry, i.e., can the patient hear sound at different standard frequencies at different volumes? The recording of these responses is graphed into an audiogram:

Image credit: Courtesy of Dr. Stephane Maison

Tests of speech comprehension can also be performed.  But more detailed tests, such as DPOAE (Distortion Product Oto-Acoustic Emissions), and BAER (Brainstem Auditory Evoked Responses) are not routinely done. They are reserved to further investigate suspected problems, or used as research techniques.

But none of these tests can detect the phenomenon of “hidden hearing loss,” a synaptopathy caused by noise damage to slow response nerves and nerve junctions in the cochlea.

Dr. Stephane Maison, a leading researcher at Harvard Medical School and the Eaton-Peabody laboratory at the Massachusetts Eye & Ear Infirmary, recently published two important papers. The first, Toward a Differential Diagnosis of Hidden Hearing Loss, documented hearing loss in young musicians that was not detected by standard pure-tone audiometry but was detected by more sophisticated tests. In his paper, Dr. Maison wrote that his study “aimed to test the hypothesis that ‘hidden hearing loss’ is widespread among young adults with normal audiometric thresholds, especially those who abuse their ears regularly.” To test this theory, they “recruited young adult subjects and divided them according to noise-exposure history into high-risk and low-risk groups.” What he and his team found were “significant deficits in difficult word-recognition tasks in the high-risk group that were associated with significant elevation of pure-tone thresholds at frequencies higher than those normally tested and with changes in auditory evoked potentials consistent with the presence of cochlear synaptopathy, also known as hidden hearing loss.”

In the second paper in The Hearing Journal, he recommends that additional tests should be added to the current audiometry protocol to detect hidden hearing loss. Dr. Maison argues that early detection must be done since “[n]oise damage early in life likely accelerates the age-related further loss of hair cells and cochlear neurons, even in the absence of further ear abuse,” and suggests that additional tests be administered to identify hidden hearing loss, noting that “recent animal research has reported regeneration of cochlear nerve synaptic connections with inner hair cells after noise exposure.” He concludes that “[c]larification of the true risks of noise, and the true prevalence of noise-induced damage, are important to public policy on noise abatement, to raising general consciousness about the dangers of ear abuse and to preventing a dramatic rise in hearing impairment in the future.”

Click the links above to read Dr. Maison’s papers. They are well worth your time.

Dr. Daniel Fink is a leading noise activist based in the Los Angeles area. He serves on the board of the American Tinnitus Association, is the interim chair of Quiet Communities’s Health Advisory Council, and is the founding chair of The Quiet Coalition, an organization of science, health, and legal professionals concerned about the impacts of noise on health, environment, learning, productivity, and quality of life in America.

 

Better Hearing Month 2017 and the problem of noise

By David Sykes, Vice Chair, The Quiet Coalition

Every year since 1927, May has been designated “Better Hearing Month.” What better time to think about what threatens your hearing health? In fact, if you already have some hearing loss you’re one of about 48 million Americans—that’s many more than all of the people with cancer or diabetes combined.

That’s a big number, and yet hearing loss—specifically noise-induced hearing loss (NIHL)–has been overlooked and underfunded for three and a half decades.

Noise is such a simple word–why is it so complex and laden with jargon and specialists who don’t talk to one another? One group is solely concerned with how to measure it (physicists). Other groups focus on specific types and sources of noise, such as jet aircraft, or alarmed medical devices, or leaf blowers, or trains, or highway noise (engineers or advocacy groups). Others concentrate on the effects of noise on humans (doctors and public health researchers), while another group ponders how noise affects organisms other than humans, including plants, birds and other animal species, including those that live underwater (biologists). Still other groups think about how to mitigate noise (architects and designers).

The problem is that over the past three and a half decades, the subject of noise and it’s effects have been systematically ignored and underfunded by Congress and the White House. As a result, “noise”–the cause of NIHL–has become a bewilderingly fragmented field in which few people talk to others outside their own specialities. This has resulted in a subject that is hard to understand and laden with technical jargon. What is “noise”? Why does it matter? Who cares? Has the science progressed? If so, how and where?

But recently that has begun to change thanks to advances in research and to changes in federal policies from several federal agencies that have not traditionally been involved in noise and noise control. These include the Centers for Disease Control and Prevention, NASA, the Department of Health and Humans Services, the Department of Interior, the General Services Administration, the Joint Commission, and others.

In each case, a specific federal department has bitten off a chunk of the noise problem and developed guidelines and programs to fit their own needs. But put all of these disparate pieces together and you will find examples of real progress despite the fragmentation.

To help build general understanding, we ar the The Quiet Coalition have assembled some of these fragments into a diagram or a “Road Map” of noise effects (see chart above) organized by the way they are studied within various specialized fields. We hope this Road Map helps others see the big picture.

In addition to the Road Map, we have also assembled the basic facts about noise into a simple one-page “Fact Sheet” that provides detailed references to scientific literature. Both the Fact Sheet and the Road Map are starting points. At The Quiet Coalition, our goal is to synthesize the underlying scientific research on this complex and fragmented subject into a coherent picture so that we can collectively find ways to talk about it. We hope you find both the Fact Sheet and the Road Map useful as you think about hearing, hearing loss, and that elusive problem, noise.

The underlying question for each of us should be: how can we work together?

David Sykes chairs/co-chairs four national professional groups in acoustical science: The Acoustics Research Council, ANSI S12 WG44, The Rothschild Foundation Task Force on Acoustics, and the FGI Acoustics Working Group. He is also a board member of the American Tinnitus Association, co-founder of the Laboratory for Advanced Research in Acoustics (LARA) at Rensselaer Polytechnic Institute, lead author of “Sound & Vibration 2.0 (2012, Springer-Verlag), and a contributor to “Technology for a Quieter America” (2011, National Academy of Engineering). A graduate of the University of California/Berkeley with graduate degrees from Cornell University, he is a frequent organizer of and speaker at professional conferences in the U.S., Europe, Asia, and the Middle East.

Is this the most thoughtful birthday present ever?

Photo credit: Dave Crosby licensed under CC BY-SA 2.0

By Daniel Fink, MD, Chair, The Quiet Coalition

In California, on his or her birthday a 16-year-old gets a driver’s license and, if he or she is lucky, a car.

One Dutch town is thinking about what may be an even better birthday present, the gift of good hearing: Dutch town considers giving birthday earplugs to all 16-year-olds.

Link via @QuietEdinburgh.

On hearing loss and the hope for a cure

In “High-Tech Hope for the Hard of Hearing,” David Owen, The New Yorker, has written an article that gives us a good look at what scientists know about hearing loss and where they are finding possibilities for treatment and, possibly, a cure. He begins his article with a series of personal anecdotes about himself, his family, and friends and the hearing problems they’ve developed due to exposure to loud noise and other factors. Owen’s interest in this story is motivated, at least in part, by his tinnitus, which is marked by a constant high-pitched ringing in his ears.

Among the advances that Owen examines, he discusses the discovery of hidden hearing loss and introduces us to Charles Liberman, who, with his colleague Sharon Kujawa, “solved a mystery that had puzzled some audiologists for years: the fact that two people with identical results on a standard hearing test, called an audiogram, could have markedly different abilities to understand speech, especially against a background of noise.” He writes that “[s]cientists had known for a long time that most hearing impairment involves damage to the synapses and nerve fibres to which hair cells are attached, but they had assumed that the nerve damage followed hair-cell loss, and was a consequence of it.” What Liberman and Kujawa discovered is that “the connections between the sensory cells and the nerve fibres that go first.” And the reason this early damage isn’t picked up by a standard hearing test is because it measures “the ability to detect pure tones along a scale of frequencies [which] requires only functioning hair cells…and is unaffected by nerve damage until more than eighty per cent of the synapses are gone.”

“A disturbing implication of [Liberman and Kujawa’s] finding is that hearing can be damaged at decibel levels and exposure times that have traditionally been considered safe,” writes Owen, but he is reassured by the researchers that the discovery of hidden hearing loss is cause for optimism. Why? “[B]ecause reconnecting nerve synapses is almost certain to be easier than regenerating functioning hair cells inside human ears.” In fact, Owen tells us that Liberman and others “have successfully restored some damaged connections in lab animals, and [Liberman] believes that far greater advances are to come.”

While cause for optimism is welcome, Owen notes something early in his article that is particularly frustrating to those advocating for regulation of noise:

There are also increasingly effective methods of preventing damage in the first place, and of compensating for it once it’s occurred. The natural human tendency, though, is to do nothing and hope for the best, usually while pretending that nothing is wrong.

Click the link above to read this interesting and hopeful article in full.

 

 

Loud sound may pose more harm than previously thought

The Associated Press (AP) reports that “[s]cientists have been finding evidence that loud noise — from rock concerts, leaf blowers, power tools, and the like — damages our hearing in a previously unsuspected way.”  The damage “may not be immediately noticeable, and it does not show up in standard hearing tests,” the AP adds, but according to Harvard researcher M. Charles Liberman,” it can rob our ability to understand conversation in a noisy setting [and] may also help explain why people have more trouble doing that as they age.”  The condition is called “hidden hearing loss,” and Liberman adds that “[n]oise is more dangerous than we thought.”

The AP interviews Matt Garlock, a 29-year old systems engineer who is “a veteran of rock concerts.”  Garlock complained of not being able to hear friends in a crowded bar, but when he got his hearing checked his test results were normal. The AP writes that Liberman’s work “suggests that there’s another kind of damage that doesn’t kill off hair cells, but which leads to experiences like Garlock’s.”  Specifically, Liberman believes that loud noise damages the delicate connections between hair cells, called synapses.  He adds that animal studies show that “you could lose more than half of your synapses without any effect on how you score on an audiogram,” but if you lose enough synapses, it “erodes the message the nerves deliver to the brain, wiping out details that are crucial for sifting conversation out from background noise.”

The end result is that people like Garlock recognize that they have a problem but their hearing appears to be fine when they take conventional hearing tests. Fortunately, Liberman says that “[o]ne encouraging indication from the animal studies is that a drug might be able to spur nerves to regrow the lost synapses.”  [Note: This article notes that Liberman has a financial stake in a company that is trying to develop such treatments.]  But while treatment for hidden hearing loss may be available in the future, what can be done now?  Liberman states that his work “lends a new urgency to the standard advice about protecting the ears in loud places.”  As always, prevention is better than treatment.

 

Another Silent Spring

By Daniel Fink, MD, Chair, The Quiet Coalition

In 1962, Rachel Carson’s “Silent Spring” described the harmful effects of insecticides and herbicides on birds, beneficial insects, animals, and humans.  Her book helped start the environmental movement. For too many people, this will be another silent spring, caused not by a dearth of birds but because people can’t hear birds sing. They have hearing loss from another environmental pollutant, noise.

Carson described how nature’s balance controlled pest species naturally, and how these species became problems only when humans changed the environment. She noted the difference between apparent short-term safety of agrichemicals and longer-term danger. People could get sprayed with pesticides or even ingest them without apparent immediate harm, with cancer and birth defects coming later.

If Carson were alive today, she might write about noise pollution, which interferes with animal feeding, communication, mating behaviors, and navigation in forests, fields, and oceans, and causes hearing loss and other medical problems in humans.  In nature’s quiet, animals developed exquisite hearing to find food or avoid being eaten. An owl can find a mouse under a foot of snow, and zebras can hear lions approaching in the veldt.

Humans are also born with excellent hearing.  Brief exposure to loud noise usually doesn’t cause obvious auditory damage in humans, but longer or repeated exposure does. The relationship between noise and hearing loss was first noted in medieval times in bell ringers and miners, then in boilermakers during the industrial revolution.  Noise wasn’t a widespread problem, and except in large cities life was usually quiet.

Industrialization, mechanization, and urbanization made life noisier.  Noise was recognized as a public health hazard in the early days of interstate highways and jet travel, but was also considered an environmental pollutant. In 1972 Congress passed the Noise Pollution and Abatement Act, empowering the Environmental Protection Agency (EPA) to establish noise standards and require noise labeling for consumer and industrial products.

During the Reagan administration, however, Congress defunded EPA noise control activities. Little has been done since to control noise, and our country has gotten noticeably louder. Sound levels of 90-100 decibels or louder are reported in restaurants, clubs, retail stores, movie theaters, gyms, sports events, concerts, and parties, from sirens, vehicles, landscape maintenance equipment, and construction, and for those using personal music players.

The National Institutes of Health states that prolonged exposure to noise at or above 85 decibels can cause hearing loss. This is misleading, because no exposure time is given and hearing damage occurs at much lower levels. The 85-decibel standard is an occupational noise exposure standard, not a safe noise level for the public.. The EPA adjusted the occupational standard for additional noise exposure outside the workplace to calculate the noise level for preventing hearing loss to be a daily time-weighted average of only 70 decibels.

Hearing is the social sense, required for spoken communication. About 40 million American adults age 20-69 have noise induced hearing loss, half of them without noisy jobs. Why is this happening? They are exposed to loud everyday noise.  Cumulative noise exposure eventually causes hearing loss, affecting 25% of those in their 60s, half in their 70s, and 80% in their 80s, and is correlated with social isolation, depression, dementia, falls, and mortality. Due to denial, stigma, and cost only 20% of older Americans with hearing loss acquire hearing aids, after an average seven-year delay, and 40% of people with hearing aids don’t use them much, largely because hearing aids don’t help users understand speech well in noisy environments.

Preventing noise-induced hearing loss is simple: avoid loud noise. If it sounds too loud, it is too loud. Free or inexpensive smart phone sound meter apps make it easy to measure sound levels, but if one can’t converse without straining to speak or to be heard, ambient noise is above the auditory injury threshold of 75-78 decibels and auditory damage is occurring.

A quieter world is easily attainable. Whisper-quiet dishwashers, cars with quiet interiors and exhausts, the Airbus A380, and a few quiet restaurants and stores prove this.   Effective noise control technologies have long existed, including noise reduction via design and material specifications and sound insulating, isolating, reflecting, diffusing, or absorbing techniques.  Indoors, all that may be necessary is turning down the background music volume, which costs nothing.

In the 1950s and 1960s, half of all American men smoked and public spaces and workplaces were filled with tobacco smoke. When research showed that tobacco smoke caused cancer and heart disease, governments restricted smoking, leading eventually to today’s largely smoke-free society. Smokers can still smoke, but can’t expose others involuntarily to their smoke.

Noise causes hearing loss. Governments should set and enforce indoor and outdoor noise standards, to reduce each person’s daily noise dose. Adults have the right to make and listen to all the noise they want, but not where others can hear them. If we can breathe smoke-free air, we can make a quieter world, so future generations won’t have to endure another silent spring.

Dr. Fink is a leading noise activist based in the Los Angeles area.  He serves on the board of the American Tinnitus Association and is the interim chair of Quiet Communities’s Health Advisory Council and the founding chair of The Quiet Coalition, an organization of science, health, and legal professionals concerned about the impacts of noise on health, environment, learning, productivity, and quality of life in America.

Originally posted at The Quiet Coalition.

Do you have hidden hearing loss?

Dstanczyk87

Photo credit: Dstanczyk87

Not sure?  One halllmark of hidden hearing loss is having difficulty hearing when you are in a noisy setting.  Recently, the Associated Press asked the Mailman Center for Child Development at the University of Miami to prepare an exercise to help readers determine how well they can hear in a noisy background. Click the link to try the exercise and see if are showing signs of hidden hearing loss.

The CDC issues report on noise-induced hearing loss

and the facts are frightening. The Centers for Disease Prevention and Control’s (CDC) current issue of Vital Signs focuses on the dangers of noise on hearing health.  Among other things, the report states that:

  • 40 million Americans aged 20-69 years old have noise-induced hearing loss (NIHL). Hearing loss is the third most common chronic health condition in the US, and almost twice as many people report hearing loss as report diabetes or cancer.
  • 1 in 2 American adults with hearing damage from noise did not get it exposure to noise at work. Noise outside of work can be as damaging as workplace noise.
  • Too much loud noise, whatever the source, causes permanent hearing loss.
  • 1 in 4 Americans who report excellent hearing have hearing damage.  You can have hearing loss without knowing it.
  • The louder the sound, and the longer you are exposed to it, the more likely it will damage your hearing permanently.
  • Continual exposure to noise can cause stress, anxiety, depression, high blood pressure, heart disease, and many other health problems.

This fascinating if distressing report comes with easy to understand graphs and charts that clearly explain the dangers of noise exposure, who is most at risk, the high cost of hearing loss, how hearing loss occurs, and, most importantly, what can be done to prevent NIHL.  Because, in the end, one point is crystal clear: noise-induced hearing loss is 100% preventable.