HEAR THE MUSIC
Marshall Chasin, Editor
"This is the best of blogs; this is the worst of blogs'. To paraphrase Dickens’s A Tale of Two Cities, it is the two-headed nature of music and hearing aids that a hearing aid can be great for speech yet useless for music, and, conversely, great for music yet less than optimal for speech. What are some tricks that can be used to improve a hearing aid for music? How can we prevent hearing loss from loud music? This blog asks these questions, and with your input, even more. Comment Policy

I love seeing 15 year old kids for a musicians’ hearing assessment. These are generally extremely talented and hard working young people who are doing everything they can to assure themselves of a life long career in some aspect of music and the arts.  Even at age 14 they are aware that the road ahead will not be smooth, with many bumps and turns, and even if they do everything “correctly”, this does not guarantee even a modicum of success.

I also love seeing 50 year old kids for a musicians’ hearing assessment. These are generally extremely talented and hard working musicians who are doing everything they can to assure themselves of a livelihood in the music industry.  And even at age 50, they are still acutely aware of the road ahead and have already experienced their share of bumps and turns in their careers, despite doing everything correctly.

Other than the obvious difference in their ages, there are also differences in what I say and do during a musicians’ hearing assessment when I see them…. or at least there “were” differences in what I said and did…

Below is a set of curves, from ISO 1999, one of several large data sets that are available, that show an interesting, and well-studied, characteristic- the hearing change from year to year in the first few years of musicians’ (or industrial workers’) careers can be large, but this change gradually decreases to the point that larger audiometric changes are no longer observed. It’s almost as if the  hearing mechanism becomes calloused and more immune to the effect of music or noise exposure.  Some researchers have referred to this as an “asymptotic” hearing loss, as if the degree of hearing loss approaches some asymptotic value.

From ISO1999 the noise exposure at averaged at 2000 Hz, 3000 Hz, and 4000 Hz for varying exposure levels from 85 dBA to 100 dBA. Note the “asymptotic” or “slowing down” of the change after 5-10 years

From ISO1999 the noise exposure and averaged at 2000 Hz, 3000 Hz, and 4000 Hz for varying exposure levels from 85 dBA to 100 dBA. Note the “asymptotic” or “slowing down” of the change after 5-10 years

Previous blogs have been based on the concept of auditory toughening where it appeared as if the cochlear mechanism was toughened up against high sound level insults. Researchers such as Henderson, Campo, Subramanian, and Spongr feature in this area of study.

The bottom line is that we don’t really know what is happening in the cochlea.   We do know (mainly from the work of Sharon Kujawa, Charlie Liberman, and Jos Eggermont) that despite there being a lessening in the cochlear susceptibility over time, including even TTS, that there can be permanent and increasing neural pathologies, which when combined with normal aging, can become quite significant years down the road.

So, as a clinical audiologist what is my responsibility?

At one point I would “read the riot act” to the younger musicians and counsel them about hearing loss prevention strategies, moderation, and hearing protection, but be more “relaxed” with those who have a few more years under their belts. After all, the ear does seem to be less susceptible over time.

Asymptotic means approaching something but never quite reaching it. Image courtesy of www.mathworld.woldfram.com

Asymptotic means approaching something but never quite reaching it.    Image courtesy of mathworld.woldfram.com

 

But the work of Kujawa, Liberman, and Eggermont clearly shows that while the cochlea may remain relatively healthy as assessed with pure tones (such as on an audiogram), the neural structures downstream are a different story.

Neural degradation is much more difficult to demonstrate in a clinical environment- especially when the appointment is only 30-45 minutes long. Certainly changes in wave I ABR can be assessed, but given the time constraints of a typical clinical environment, this will typically not be done.  One can argue that in a perfect world it should be done but at some point a clinical decision needs to be made about what is important (at least for educational and counseling concerns) and what has less importance.

The data in the figure from ISO 1999, and which has been replicated by others such as Ulf Rosenhall, are important but no longer feature prominently in my clinic. At one point I would  have a laminated sheet showing this graph- actually the one I had was from Rosenhall- but I have decided to “hide”  this information from my clinical population.

Simplistic nature of pure tone results. Image courtesy of the-penultimate-word.com

Simplistic nature of pure tone results. Image courtesy of the-penultimate-word.com

I am not making a clinical “error of omission” but I do feel that these data are quite misleading. Pure tone audiometric results are just overly simplistic, and while I once felt that TTS was just a “benign” characteristics of music or noise exposure and not useful, I also feel that showing a graph depicting asymptotic hearing loss is simplistic and not the true story.

In part 1 of this two part blog series, the characteristics of temporary hearing loss, also known as Temporary Threshold Shift (or TTS) were discussed. Using pure tone stimuli, TTS typically resolved in 16-18 hours – it was thought to be nothing more than a benign characteristic of noise or music exposure, with no predictive power.  And while this was true of the research done prior to 2000- namely that cochlear sensitivity resolved using pure tones- research performed more recently examines the characteristics of the neural hookups between the inner ear and the brain.  It is these neural connections and structures that suffer permanent degradation even after the pure tone thresholds due to noise or music exposure have resolved.

In view of the newer research on TTS over the last 10-15 years an app has been developed where TTS can be measured by anyone, using a Smartphone and any set of earphones (available from the Apple Store for the iphone and from the Google Store for Androids).

Start up screen of the Temporary Hearing Loss Test app

Start up screen of the Temporary Hearing Loss Test app

Using earphones a person can, within several seconds, measure their hearing threshold at 6000 Hz, and this number is saved.   Without changing the volume setting on the Smartphone, the person goes to work in a factory, listens or plays music, or goes to a sporting event, and then immediately after the event, the hearing acuity is measured for a second time, and saved.  This difference is a measure of TTS.

Because the app uses a “difference” between two measurements, no calibration is required.  Measurements are valid as long as the Smartphone volume control has not been changed, and the “before” and “after” measurements were performed in similar environments.

Depending on the degree of TTS one of three screens will be shown- green colored for minimal TTS (<5 dB); orange colored for some degree of TTS (6-15 dB); and a red screen for TTS that is greater than 15 dB. Each screen has information about hearing loss prevention as well as a link to the FAQ page at the www.MusiciansClinics.com website.  The data from the TTS measurement can be emailed along with the duration between the first and second parts of the test.

 

 

Using the Temporary Hearing Loss Test app individuals can now quickly assess whether the noise or music exposure resulted in a change in hearing acuity.   And while repeated TTSs may only last 16-18 hours, as shown by Kujawa and her colleagues, long term neural damage may ensue.  This app is not intended as a replacement for industrial assessment of the noise or of the dose, but does provide one more important piece of the hearing loss prevention puzzle.  The Temporary Hearing Loss Test app simply addresses the important issue of whether there is TTS or not and how much, and this is evaluated on an individual basis.

Result screen (red) showing greater than 16 dB TTS along with hearing loss prevention information

Result screen (red) showing greater than 16 dB TTS along with hearing loss prevention information

While it is true that changes in puretones are a simplistic measure of the effects of loud noise or music, they can be used to assess TTS and can provide information to minimize long-term neural changes, and ultimately sensory changes in the hearing mechanism. These changes may result in tinnitus, hyperacusis, or eventual permanent hearing loss.  More information can be found at www.MusiciansClinics.com.

NOTE:  The editorial board at www.HearingHealthMatters.org have graciously allowed me to talk about the Temporary Hearing Loss Test app and I do have to state that this app was developed by myself at the Musicians’ Clinics of Canada.  All proceeds go to supporting hearing health care activities through my Musicians’ Clinics. (Marshall Chasin, AuD).

 

 

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