We can’t always measure a hearing loss

This guest blog is by Patricia Johnson… and it is about things that may go wrong in your hearing system that we don’t clinically have the ability to assess.  Dr. Johnson received her Master’s degree in Audiology from the University of Iowa and her AuD from Salus University.  Her professional experience spans pediatric and educational audiology, industrial hearing conservation, university teaching and private practice.  At Etymotic Research she is involved in research, education, technical writing and new product development.

The start of a new calendar year is often seen as an occasion for change. At this time of year many people examine their lives, actions, and beliefs, and resolve to make a few changes. Somehow, the flip of the calendar to a new year encourages us to get rid of the old and embrace the new. Many people resolve to exercise, eat better, or make other healthy lifestyle changes. What are your New Year’s resolutions? What old things do you want to get rid of, and what new things do you want to embrace?

I’ve experienced a lot of change over the years. Those who’ve known me a long time first knew me as Patty Tillman (no relation to the venerable Tom Tillman, unfortunately). Being somewhat of a traditionalist, I became Patty Niquette when I married in 1995. After my divorce I kept Niquette for the sake of my young children. But time marches on, and I’m now embracing another change: in April I married the nicest guy on the planet (trust me, he is, because I don’t believe in making the same mistake twice). From here on out you’ll know me as Patty Johnson. I’ll try to ease the transition by using Patty Niquette Johnson, but only because Patty Tillman Niquette Johnson is too many last names for anyone. Same person, just better, healthier choices.

Speaking of better, healthier choices: how’s your hearing? Those of us in the hearing healthcare industry aren’t immune to the ravages wrought by excessive noise exposure. You don’t think you’re over-exposed? Really? Do you remember the last professional convention you attended? Were there any social functions that were loud? Was your hearing muffled afterwards? Did you have tinnitus? How many of you use power tools, lawn mowers or snow blowers? Loud vacuum cleaners? Loud, whirring blenders for an extended margarita party? How many of you attended your kids’ sporting events this past year? Concerts? Live music? All of these have the potential to give you a noise overdose. The ringing and muffled hearing? That’s a noise hangover. Sure, your ears seem to recover, but at what cost?

It’s time to discard our old assumptions, beliefs and practices regarding noise exposure, and adapt healthier beliefs and practices. We used to believe that Temporary Threshold Shift (TTS) was, well…temporary. Sure, our ears would ring and our hearing would be muffled after those big social events at professional conventions. But that was just temporary. Or was it? Research on noise exposure by Kujawa and Liberman (2009) challenges our old assumptions and begs us to rethink the concept of TTS. Kujawa and Liberman found that while outer hair cells do recover from noise exposure after a period of rest (with a corresponding recovery of hearing thresholds and otoacoustic emissions [OAEs]), other changes in the basal region of the cochlea do not recover: they found dramatic degeneration of both pre- and post-synaptic elements of the inner hair cells and spiral ganglion cells. Not only is this damage undetectable using current test protocols (pure tone thresholds, OAEs and auditory brainstem response [ABR] testing) but the loss of spiral ganglion cells is not seen until weeks or months post-exposure. Kujawa and Liberman suggest that noise-induced hearing damage has progressive consequences that we cannot clinically measure, and that may not be evidenced until much later. This damage is likely to be eventually expressed as difficulty hearing in noise and/or tinnitus or hyperacusis.

Yikes! If that doesn’t motivate you to throw off the old nonchalance and embrace a healthier hearing lifestyle, I don’t know what will. But how do you know if your ears are receiving an overdose? After all, what seems too loud to one person may seem “just right” to someone who likes things a bit loud. Well, there’s an app—and a product—for that.

A recent search for iPhone apps using “SPL meter” as the search term produced 47 apps, ranging in price from “free” to $19.99.  I like “SPL Meter” by Andrew Smith, which I’ve used for the past several years. This free app is similar in appearance to the old analog Radio Shack sound level meter (sadly, no longer available) and provides the same results when I’ve compared the two side-by-side. It’s extremely handy and a wonderful tool to get a quick reading on sound levels. But what to do when sound levels fluctuate, and you’re not sure if you really need hearing protection? For that, you’ll need to use a dosimeter.

Noise dosimeters measure and integrate sound levels over time, and provide an estimate of noise dose. For an explanation of noise standards and noise dosimetry, I recommend you read an excellent paper written by someone named Patricia Niquette.

Many hearing professionals are unfamiliar with noise dosimeters, as their use has been seemingly relegated to noise control engineers and those who work in industrial hearing conservation. Also, dosimeters have traditionally been complicated to use and costly to purchase. Etymotic Research developed the ER-200D, a small, lightweight, inexpensive dosimeter that’s easy to use. Data stored on the device can be downloaded and printed, and I’m sometimes amazed at the results.

You might think concerts are pretty loud, and you’re right. But do you have any idea how loud? I do. One of my colleagues at Etymotic frequently attends live music events with his twenty-something son, and he always wears a noise dosimeter (and earplugs). Results of one of the quieter all-day music festivals he attended are shown in Figure 1.

While the level wasn’t high as far as concerts go, the amount of time spent in the noise produced a final dose of 1,000%, which translates to two weeks’ worth of noise exposure in a single day. Too much? I’d say so. But with earplugs, he and his son were just fine. We might even call this a “lullaby” music festival. Another festival they attended wasn’t quite so kind, auditorally speaking: this headbanger of an event, shown in Figure 2, had an equivalent continuous level of 107 dB. Over the course of their day-long attendance, this produced a noise dose of 13,000%. That’s 26 weeks’—or 6 months—worth of noise exposure in a single day! With ER-25 Musicians Earplugs, however, their hearing wasn’t at risk.

This is an extreme example, so I’ll close with something far less innocuous, yet unexpected: results of noise dosimetry at a small middle-school basketball game, where the referees’ whistles, scoreboard buzzer and crowd noise produced an equivalent continuous level of a measly 91 dB (See Figure 3).

Over the course of an hour, the sound level at this middle school basketball game produced a noise dose of 91%. A pittance, compared to the concerts. But wait—this was a tournament day, so most of the children and adults at this event watched several games, some as many as five or six. Suddenly, that 91% (almost an entire days’ dose) doesn’t seem like such a pittance after all.  Most of the attendees likely received a noise overdose; those attending five or six games, an entire weeks’ worth.

Does this get you thinking about your own noise exposure, and the noise exposures of your loved ones? I hope so. We have the tools. As hearing health professionals, let’s all resolve, during the coming year, to do a better job of measuring noise exposures and promoting and using hearing protection so we can all have a healthier hearing future.