The ear gets tough- part 1

At the last National Hearing Conservation Association (NHCA) meeting in New Orleans I had the opportunity to run in to Ulf Rosenhall in the elevator. Having never met him, I recognized him by his name tag, and immediately started to tell him about his excellent 1990 study, in perhaps more detail than I should have. Unfortunately for Dr. Rosenhall, his floor was the top one so he had to put up with me for quite some time. After the security staff left and it was determined that I was harmless, we did sit down in the lobby for a chat. Lobbies are great since there are many ways for him to escape from me.

This only happened to me once before, where I was so completely uncool that it was embarrassing. The last time was with Ray Dolby, the guy who solved the noise problem on tape media, and I am sure that the restraining order has long expired.

What I found most exciting about meeting Dr. Rosenhall was that his work was so applicable to every day clinical work that I, and most of my colleagues, were involved in.

This is what he found in 1990.

Dr. Rosenhall and his colleagues (Kai Petersen and Alvar Svanborg) found that hearing loss from noise exposure (and presumably music exposure) is “asymptotic”. That is, the hearing loss change from year 1 to year 5 of exposure may be great, but the hearing loss change from year 6 to year 10 was even less. Hearing loss continued to deteriorate as long as the worker was exposed to loud noise but the greatest measured change seemed to have occurred in the first several years. After 10 or more years of progressing hearing loss the changes were less and less. It’s almost as if the cochlea was becoming immune to further hearing loss; as if it was “toughening” (but see part 2 of this blog series for those experiments).

Essentially it says that we must be very diligent in the early years to educate about the potential of hearing loss, but that we can sit back and be less stringent when we see someone who already has been around for a decade or so.

Of course this is an exaggeration- pure tone audiometry is one of the weakest indicators of sensory and neural damage. There are a multitude of pathological changes that are occurring neutrally in the processing, and also bio-mechanically in the cochlea, ranging from hair cell dysfunction to a change in the function of the stria vascularis.

However, something is definitely happening that the acuity ceases to continue to decrease, or at least to decrease at the same rate. It’s almost as if the cochlea is becoming “toughened”, at least metaphorically.   And speaking of toughening, I ran into Dr. Campo when I was at the World Congress of Audiology in 2014 in Brisbane, Australia, but that is part 2 of this blog series! (Australian security staff isn’t as nice as those in New Orleans…)

 

Based on the data from ISO 1999, Rosenhall and colleagues noted that eventually permanent hearing loss becomes "asymptotic" where changes gradually become less over the years.

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About Marshall Chasin

Marshall Chasin, AuD, is a clinical and research audiologist who has a special interest in the prevention of hearing loss for musicians, as well as the treatment of those who have hearing loss. I have other special interests such as clarinet and karate, but those may come out in the blog over time.