Hard At Work

Here is the second dose (get it?) of my summaries. This puts me up to date for all the articles I have read so far. Time to gather more! :)

1. Recreational noise exposure and its effects on the hearing of adolescents. Part II: Development of hearing disorders. Ester C Biassoni et al. Int'l Journal of Audiology (2005)

This study was a follow-up to the one in Argentina looking at the undue amount of hearing loss in young adults. As much as has been found about NIHL, the author writes, “...the auditory system is much more adaptable than currently assumed, therefore it recognizes the danger of intensive sound and adapts to the situation by reducing its sensitivity.” Even so, the research shows that young adults are exposing themselves to extreme noise in settings such as discotheques and concerts.

An interesting point that this study raised was that there is data which indicates, “...that the supersonic components of the music spectrum may have substantially contributed to the damaging effects of the exposure.” Sound we aren't even measuring could be greatly-affecting how much we're damaging our hearing. This allows for the possibility of sub-damaging levels of noise to still affect us.

Later on, the authors explain that the group with the worst thresholds (those deemed to have 'tender ears') exhibited elevated thresholds in the 8000-16000Hz range, extending lower into the conventional range of hearing. This, the authors state, “...could act as an early predictor of future development of hearing loss in the speech-understanding frequency range,” which is of most concern to clients.

Knowing that this loss happened between ages 14 and 17, this study provides evidence for the need to test students before they are pushed out into the 'real world,' when they can still gain help through the school system. There is also evidence for a hearing conservation (hearing loss prevention) program in the schools, perhaps blended into biology courses. It would also be helpful to limit the noise level in loud places, such as concerts, 'discos'/bars, etc. Even reducing noise levels at rock concerts from 117 dBA (equivalent to the discotheques in the other studies) down to 106 or 103 dBA would be helpful, due to the 3 dB exchange.

2. Characteristics of the audiometric notch as a clinical sign of noise exposure. David McBride and Sheila Williams. Scandinavian Audiology (2001)

This study was an evaluation of 1,600 audiograms (634 noise-exposed employees, each with two ears), the purpose of which was to investigate variability in the noise-induced hearing loss 'notch'. Traditionally, the first sign of noise-induced hearing loss is at approximately 4KHz, where the audiogram develops a small notch that gets deeper and wider as the damage continues. The authors chose three raters (an otolaryngologist, and audiometrician, and an occupational physician) to interpret the audiograms and determine whether or not the dip is related to noise exposure. The three features the interpreters looked for were the frequency at which it occurred, the depth, and the shape of the curve.

I found an unexpected piece of information while reading this article. The first rater (the ENT) classified 26% of the audiograms as NIHL, whereas the occupational physician classified 68% as NIHL, with more notches identified at every frequency and no specific criterion for depth or shape in mind as he/she rated. This is evidence for why occupational audiologists are needed as opposed to unrelated professions which are slated for an audiologist's job. I think this would be an important statistic to show in advocacy situations. Not only are we better-trained, we can save the companies money by not over-referring!

Either way, the high variability suggests that audiometric shape cannot be used as a method for diagnosing noise-induced hearing loss. As Alberti (1997) states (as quoted by the authors), “This supports the contention of Alberti, who has long been of the opinion that audiometric shape may only be a guide, and not a major diagnostic factor for, for NIHL.”

3. Supplement: Program for the Conservation and Promotion of Hearing Among Adolescents. Mario R Serra et al. American Journal of Audiology (2007)

This supplement was another piece in the “Recreational Noise Exposure and Its Effects...” done in Cordoba, Argentina and involving 14-year-old students in a semi-longitudinal study over three years. As the authors state, there were two noticeable findings: “1. There was a higher tendency of more sensitive ears to be affected at an early age... 2. The efficacy of audiometry in the extended high-frequency range was an early predictor of hearing loss.” The latter is probably the most important clinically, but the former is important to keep in mind as we discuss the issue of noise exposure in young adults. Some sources state that young ears are less fragile, and others state that fragile ears are more susceptible while young.

This article taught me a few things about noise exposure that I hadn't quite learned yet. Namely, the authors explain, “While TTS typically resolves within a few hours or a day after exposure, there is no agreement among researchers whether repeated TTS bears a risk of permanent threshold shift.”

4. Effect of a hearing protection campaign on the discotheque attendance habits of high-school students. Viktor Weichbold, Patrick Zorowka. Int'l Journal of Audiology (2003)

This was an ambitious study with high hopes that unfortunately failed to deliver. The goal was to pilot a hearing loss prevention program in six high schools in the Italy/Austria area called “PROjectEAR” and hope that it changed young people's opinions about hearing protection and loud noise. There were four 45-minute sessions spread over 3 days which presented several different approaches to protecting one's hearing. An interview was conducted post-campaign with 136 students although all of the students in the schools participated.

While the percentage of students who attended discotheques frequently lowered from 34% to 24% after the campaign, statistical analysis does not support the idea that there was a significant change. The authors state that, “..the changes observed in our sample may be due to the random variation rather than to a systematic effect of the hearing protection campaign.” In addition to that discouraging finding, less than 4% of the students took the advice to use ear plugs or other hearing protection in the discos.

The authors explain that there is no control group for this study because there was too much information-sharing between students participating and those were not. Also, although, “...the campaign had no important effect in inducing hearing-protective behaviors in pupils when attending a discotheque,” one of the other studies found that students were willing to take more 'regeneration breaks' after the program and have the discotheques reduce their sound floor, so perhaps that is an area to target.

A quote I really liked that I wanted to include for the sake of aesthetics is, “At this point, a tragic irony becomes obvious. The pupils experienced the negative effect of bad hearing on communication when they tested earplugs for hearing protection in the discotheque. Being annoyed about the impaired communication, they dismissed the earplugs.”

5. Noise exposure levels from personal stereo use. Warwick Williams. Int'l Journal of Audiology (2005)

This study aimed to look at worst-case scenarios of personal media players, such as listening in the presence of relatively loud background noise. In this case, the background noise was approximately 73.2 dB, but varied from 71.1 to 76 dB. Fifteen females and forty males were asked to participate in the study (mean age 23.6 years), which meant allowing their headphone output to be measured and filling out a short survey of their listening habits. The average volume turned out to be only 79.8 dB, but approximately 25% of the population was still estimated to be “at-risk,” by listening to music over 85 dB.

Also of note is that the males (the larger group) listened to their music at 80.6 dB on average as opposed to females ,who listened at 75.3 dB. Perhaps if more people were studied, this average would sneak up?

The authors state in the conclusion that, “While some individuals do expose themselves to significant risk of noise injury by using earphone levels at high settings, the data collected in this study does not indicate that for the majority of typical users there is a significantly increased risk of hearing loss due to PSP (personal stereo player) use alone.” Unfortunately, those people who may lie on the boundary line are at risk in other areas of their lives because people who listen to their music loudly are more likely to listen to their television loudly, etc.

6. Effects of Exercise and Noise on Auditory Thresholds and Distortion-Product Otoacoustic Emissions. Shannon Hooks-Horton et al. Journal of American Academy of Audiology (2001)

This study isn't totally connected to the research I'm doing, but I found it hilarious that the authors actually address, “It is also the case that ovarian and contraceptive cycles may play an additional role in TTS shift in females, however this factor was not controlled in the present study,” and that the TTS shift for ovarian cycles was actually investigated by two different studies: Petiot and Parrot (1984) and Hori et al (1993). How funny is that!

Oh, and by the way, the authors found that there is no significant connection between exercise and noise-susceptibility.