EXPERT ROUNDTABLE: Music & Hearing | February 2017 Hearing Review

TTS may not be a direct predictor of hearing loss, but it does point to neural pathologies.

By Marshall Chasin, AuD

Temporary hearing loss can no longer be considered to be a benign temporary audiometric characteristic. Although it has not been established that TTS can be a predictor of future hearing loss, its presence does point to sometimes subtle neural pathologies that may result in future communication degradation.

One does not need to go back to a noisy workday in 1917 to compare it with a similar setting in 2017 when it comes to temporary threshold shift (TTS). TTS is the “temporary” reduction in hearing sensitivity that typically occurs after a loud rock concert or a day at a factory. It is typically measured as a difference in hearing thresholds before an exposure and then again after an exposure.  Of course, prior to the 1950s, audiometers or other calibrated measurement devices were not widely available to ascertain the degree of TTS.  Nevertheless it would not be surprising for someone in 1917 to report that their ears were feeling numb, perhaps had tinnitus, and a feeling of reduced hearing after a noisy day at work.

TTS has been well studied and has been a useful research tool—many of the earlier studies would look at estimates of TTS with humans in the same way that they would look at permanent threshold shift (PTS) or permanent hearing loss in laboratory animals. Research performed as far back as the 1970s have delineated some of the features of TTS, and of its resolution.1  Typically TTS resolves after 16-18 hours and has been related to excessive levels of glutamate in the inner ear as well as temporary dysarticulations between the outer hair cells and the tectorial membrane.2

Conclusions of many researchers in the last century, such as those of Dixon Ward,1 Erik Borg,3 and colleagues suggest that there are no lasting effects of TTS, and that it is a benign side effect of overexposure. The most that could be said is that, prior to having a permanent noise or music related hearing loss, one first needed to experience TTS.

”Figure

This new century brought with it measures of TTS that go beyond the simple pure-tone audiogram; specifically, suprathreshold neural structures. Research by Kujawa and Liberman4,5 and others have demonstrated that, while cochlear function (and puretone hearing loss) does resolve after TTS, neural pathology can remain. Specifically it was found that, even after puretone thresholds have returned to a pre-exposure state, there can still be:

  1. Rapid inner hair cell (afferent) synaptic loss;
  2. Rapid inner hair cell dendritic loss;
  3. Slow spiral ganglion cell loss, and
  4. Persistent reductions in suprathreshold neural responses (ie, reduced wave I ABR).

Temporary hearing loss can no longer be considered to be a benign temporary audiometric characteristic. Although it has not been established that TTS can be a predictor of future hearing loss, its presence does point to sometimes subtle neural pathologies that may result in future communication degradation.

An app (available on both Apple and Android/Google) called Temporary Hearing Loss Test6 has been developed by the author to allow any Smartphone user to assess their TTS as a result of noise or music exposure—and this is something that I suspect was not around in 1917.

References”Marshall

  1. Ward WD, Cushing EM, Burns EM. Effective quiet and moderate TTS: Implications for noise exposure standards. J Acoust Soc Am. 1976;59:160-165.

  2. Chasin M. Hearing Loss in Musicians: Prevention and Management. San Diego: Plural Publishing Inc;2009. ISBN #978-1-59756-181-5

  3. Borg E, Canlon B, Engstrom B. Noise-induced hearing loss: Literature review and experiments in rabbits. Scand Audiol. 1995;40 [Suppl]:1-147.

  4. Kujawa SG, Liberman MC. Acceleration of age-related hearing loss by early noise exposure: Evidence of a misspent youth. J Neurosci. 2006; 26(7):2115–2123.

  5. Kujawa SG, Liberman MC. Adding insult to injury: Cochlear nerve degeneration after “temporary” noise-induced hearing loss. J Neurosci. 2009; 29(45):14077-14085.

  6. Chasin M. A temporary hearing loss test app. Hearing Review. 2016; 93(6):32.

CORRESPONDENCE can be addressed to Hearing Review or Dr Chasin at: [email protected]

Citation for this article: Chasin M. Temporary threshold shift (TTS) is NOT so temporary. Hearing Review. 2017;24(2):22.

 

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Expert Roundtable: Music & Hearing (February 2017 Hearing Review)

Expert Roundtable: Music & Hearing on the 100th Anniversary of Recorded Jazz, By Marshall Chasin, AuD, Bethany Ewald Bultman, and Dan Beck, Guest-editors

Jazz: An Acoustical Revolution, By Bethany Ewald Bultman

The Evolution of Hearing Conservation Guidelines and Standards in the United States, By Mark Stephenson, PhD

A Historical Perspective on Hearing Protection, By Patricia A. Johnson, AuD

Ear Infections Over the Ages, By Kenneth Einhorn, MD

Promoting Safe Sounds in the Birth City of American Music, By John J. Hutchings, MD, and Bethany Ewald Bultman

Temporary Threshold Shift (TTS) Is NOT So Temporary, By Marshall Chasin, AuD

Have We Really Come That Far? By Dan Beck