Tag Archive: 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.

 

Modern life is damaging our ears more than we realize

Photo credit: Global Jet

Rebecca S. Dewey, a research Fellow in Neuroimaging writing for The Conversation, addresses noise exposure, “the main cause of preventable hearing loss worldwide.” She cites a recently published study in The Lancet that “revealed that living in a noisy city increases your risk of hearing damage by 64%.” Why do cities increase the risk so dramatically? Dewey points to obvious sources–work noise at a construction site or recreational noise at a nightclub–but adds that people “might be exposed to loud noises so constantly throughout the day that you don’t even realise they are there.” She also notes that many of us engage in “self-harm”–that is, exposing ourselves via mp3 players and mobile phones to damaging noise levels “with little more than a disclaimer from the manufacturers.”

Why is this a concern? Because of strides researchers have made about how hearing loss develops, aided by the relatively recent discovery of “hidden hearing loss.” Dewey states that it used to be believed that “noise-induced hearing loss resulted from damage to the sound-sensing cells in the cochlea,” but recent studies have shown that “even relatively moderate amounts of noise exposure can cause damage to the auditory nerve – the nerve connecting the inner ear to the brain.”

Unfortunately, the standard audiology exam “measures hearing by finding the quietest sound a person can hear in a quiet environment,” but hidden hearing loss affects “the ability to hear subtle changes in loud sounds,” what is called “supra-threshold.” Supra-threshold hearing is used to “understand conversations in a noisy room or hear someone talk over the sound of a blaring television.” In short, a traditional hearing test can’t detect hidden hearing loss, and attempts to measure it by playing a recording of speech masked with background noise “depends a lot on the ability of the patient to understand and cooperate with the test.”

Fortunately, Dewey works on a team at University of Nottingham that is developing an objective test using MRI scans that will “detect hidden hearing loss by scanning the parts of the hearing system that connect the ears to the brain.” The goal is to “understand who is most at risk and act early to prevent further hearing loss.”

And prevention is key, because there currently is no treatment or cure for hidden hearing loss. So do yourself a favor and avoid loud noise when you can, use earplugs when you cannot, and lower the volume on your personal audio devices. One day there will likely be a good treatment available for hearing loss, but no one knows if that day is five, ten, 20, or more years away. Why gamble on a future cure when prevention works today?

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.

 

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.

Age doesn’t matter,

you could have hidden hearing loss (and not know it). WMAR Baltimore reports on hidden hearing loss, a relatively recently discovered hearing breakthrough that explains how people who pass hearing tests have problems hearing in noisy environments.  WMAR interviewed audiologists about this breakthrough, who said that “why patients can’t decipher speech in noisy situations has been unexplained, but a new breakthrough is changing that.”  The researchers who made the hidden hearing loss breakthrough studied young adults who were regularly overexposed to loud sounds, and found that “hidden hearing loss is associated with a deep disorder in the auditory system.”

It’s never too late to protect the hearing you have.  Exposure to loud sounds damages hearing.  Period.

 

Declining prevalence of hearing loss in U.S.? What do the data really show?

by Daniel Fink, MD

On December 16, 2016, an article appeared in the New York Times, Americans’ Hearing Loss Decreases Even With Ubiquitous Headphones, which focused on a study by Howard J. Hoffman, MA, et al. (Hoffman) that appeared in the respected medical journal JAMA Otolaryngology–Head & Neck Surgery. The study found that there was a declining prevalence of hearing loss in U.S. adults. The results were considered surprising, as the study showed that the rate of hearing loss in adults age 20-69 had decreased from 15.9% to 14.1%. The researchers, epidemiologists, and statisticians at the National Institute for Deafness and Other Communication Disorders, who conducted the study, are among the best in the world, and the data came from the Centers for Disease Control and Prevention’s well-respected National Health and Nutrition Surgery.

The results were considered surprising because two other recent federal reports, one in October 2015 from the President’s Council of Advisors on Science and Technology (PCAST) and the other in June 2016 from the National Academy of Science’s Institute of Medicine (IOM) (since renamed the Health and Medicine Division), emphasized that hearing loss, especially in older Americans, was a major national problem. Both of these reports cited an analysis by Frank Lin, MD PhD, Johns Hopkins University, that showed that 48 million Americans suffered significant hearing loss, with the prevalence increasing sharply with age.

I am personally involved in the question of what the facts are, since in an editorial in the January 2017 issue of the American Journal of Public Health I write about the inappropriate use of the 85 decibel occupational noise exposure standard, which should not be applied to the general public, citing Lin’s research and other studies that show increased hearing loss in young people age 12-19.

So, what do the data really show?

I am not an epidemiology expert like Mr. Hoffman and his distinguished co-authors. Their methods appear sound, their data sources as good as one can find in the epidemiology of hearing loss. The first caveat is that this study, as with all studies of the epidemiology of hearing loss in the pubic, is based on survey methodology. A group of 3831 participants are the study population, from which conclusions about the entire U.S. population were drawn. It would be too costly to test hearing in millions of people.

The second caveat is that there are newer techniques, currently only used in research and not yet in clinical use, demonstrating that before hearing loss can be detected by standard hearing tests (called pure tone audiometry), a phenomenon dubbed “hidden hearing loss” may have taken place. Hidden hearing loss has been found in young people and older adults. So while Hoffman’s study is encouraging, it may not be able to completely report what is really happening with Americans’ hearing.

The third point–not a caveat–is that Hoffman et al. studied adults age 20-69 and did not include young people under age 20. Those under age 20 may be the group most at risk of hearing loss due to ubiquitous use of personal music players at loud volumes. Two studies, using lower thresholds for measuring hearing loss than Hoffman et al. or Lin et al. used, found high levels of subclinical hearing loss (hearing loss greater than 15 decibels but less than 25 decibels) in young Americans. One from 1998 found that 15% of young people had measurable hearing loss, and the other from 2010 showed an increase in the prevalence of hearing loss to almost 20%. This is worrisome because studies of auditory acuity in young people traditionally found excellent hearing.

The fourth point also isn’t a caveat, but a quote from the last line of Hoffman’s abstract: “Despite the benefit of delayed onset of HI (hearing impairment), hearing health care needs will increase as the US population grows and ages.”

It’s great news that the percentage of Americans age 20-69 with hearing loss (the epidemiology term for this is “prevalence”) has decreased from 15.9% to 14.1%. But that still means that there are millions of Americans with hearing loss–and that’s too many! Further, subclinical hearing loss appears to be increasing in young Americans, and, as the Hoffman study notes, hearing loss in older Americans is a significant health problem.

Finally, a point of contention: noise exposure is a major cause of hearing loss, and not aging as is implied in the study. Why would men have nearly twice as much hearing impairment (18.6%) as women (9.6%)? Is it an effect of testosterone levels on the auditory system, in which case one might actually expect hearing to improve as men get older, or is it the result of more noise exposure from work and recreational activities in men than women? Noise and hearing loss are still major problems in the U.S. and in the world, and the non-auditory effects of noise on health, which are coming into greater focus, continue unabated. 

So yes, the prevalence of hearing loss in American adults may be declining, but when Lin’s analysis showed that approximately 25% of adults in their 60s, 33% of adults in their 70s, and half of those over age 80 have significant hearing loss–data cited in the PCAST and IOM Committee reports–it is obvious that there is still a major problem and still much to be done to prevent noise-induced hearing loss here and abroad.

And I and others have said before, but it bears repeating: noise-induced hearing loss is 100% preventable. If people avoid noise exposure and protect their ears from noise, they should be able to preserve natural hearing well into old age, rather than needing to rely on assistive hearing devices. The only evidence-based safe noise level remains a 70-decibel time-weighted average for a 24-hour period.

Dr. 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 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.

Hearing test developed to detect hidden hearing loss

UConn School of Medicine researchers develop first hidden hearing loss hearing test. EurekAlert! reports that “[t]wo researchers at UConn School of Medicine have developed a new hearing test that can identify hearing loss or deficits in some individuals considered to have normal or near-normal hearing in traditional tests.”  Leslie R. Bernstein, professor of neuroscience and surgery at UConn, who conducted the study with Constantine Trahiotis, emeritus professor of neuroscience and surgery, explained the importance of the new test by noting that “acquired hearing loss from excessive noise exposure has long been known to produce significant, and sometimes debilitating, hearing deficits.”  EurekAlert! writes that the “new research suggests that hearing loss may be even more widespread than was once thought,” adding that with this new test, there now is a “validated technique to identify ‘hidden’ hearing deficits that would likely go undetected with traditional audiograms.”