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|Year : 2009 | Volume
| Issue : 44 | Page : 129--131
Personal listening devices and hearing loss: Seeking evidence of a long term problem through a successful short-term investigation
Brian J Fligor
Children's Hospital Boston, Instructor in Otology and Laryngology, Harvard Medical School, USA
Brian J Fligor
Director of Diagnostic Audiology, Children's Hospital Boston, Instructor in Otology and Laryngology, Harvard Medical School
|How to cite this article:|
Fligor BJ. Personal listening devices and hearing loss: Seeking evidence of a long term problem through a successful short-term investigation.Noise Health 2009;11:129-131
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Fligor BJ. Personal listening devices and hearing loss: Seeking evidence of a long term problem through a successful short-term investigation. Noise Health [serial online] 2009 [cited 2021 Mar 6 ];11:129-131
Available from: https://www.noiseandhealth.org/text.asp?2009/11/44/129/53356
An impressive amount of attention has been given to risk for noise-induced hearing loss (NIHL) from abusive use of portable listening devices (PLD), also known as personal music systems (PMS) in the paper published by Kumar et al .  This author was privileged to write one of the articles to be published early in the renewed debate over hearing loss risk from headphones.  The controversy, of course, is not whether or not headphones are capable of causing NIHL (they are), but whether or not they do to such a degree as to warrant the public's attention. A valid concern is that stories about "headphones and hearing loss" draw attention away from more certain causes of NIHL, such as occupational and military noise exposure. Conversely, perhaps the attention given to "headphones and hearing loss" has served to raise the public's awareness that all intense sound can damage hearing, and thus should (one hopes) eventually assist the efforts of hearing loss preventionists in all sectors of society (in line with the stated mission of the National Hearing Conservation Association in the United States " www.hearingconservation.org "). It would appear, in the short term, that the debate is one of relevance.
Damage risk criteria (DRC) generally describe hearing damage risk accumulating over a 40-year time span. This span is certainly an order of magnitude (or two) too long for the popular media and adolescents, and yet it is much too short to apply to children and teenagers, who stand to live several decades past this span of 40 years. The criticisms of applying occupational DRC are noted (there is no DRC specifically for music exposures) and so, it is possible that music does not damage hearing to the same degree as occupational noise at the same intensity and duration. It is also unclear that assigning maximum "safe" level-duration combinations intended to limit the degree of noise-induced permanent threshold shift (NIPTS) would be appropriate to apply to recreational sound exposure. Some might argue that any NIPTS from such recreational exposures should be avoided, given all the other, less easily prevented, causes of sensorineural hearing loss.
Imagine a 13 year-old who finally, after much patient waiting, is given a cell phone and PLD by his parents. He invests much of his time and spending money downloading music and other audio content. He listens to his music to and from school, while doing chores, and often when doing homework. He does this every day. Does this behavior seem plausible? Is this 13 year-old's hearing at risk? As we all know, that depends…
Data published in peer-reviewed literature have shown no correlation between chosen listening levels and typical daily or weekly listening duration. The data have shown that a small percentage of people choose "high" levels (this author defines "high" as levels sufficient to risk NIHL if listening duration is long enough). Data have also been presented that people listen from one to 21 hours per week. , In those individuals who listen for longer durations at higher levels, it is reasonable to consider that some of these people are at risk. As noted in the introduction, controversy exists as to how many people this risk category constitutes.
Felchlin et al .  showed an average exposure of 72 dB(A), 8 hn with 10% of their 350 subjects exceeding 85 dB(A) Leq, 8 hn, and 5% exceeding 87 dB(A) Leq, 8 hn with cassette tape players. Likewise, Williams  showed an average of 79.8 dB(A), 8 hn exposure in users of MP3 players (iPods and the like), with 25% of users exceeding 85 dB(A), 8 hn. These estimations of noise exposure were based on a combination of objective measures (free-field equivalent sound level measurements) and subjective measures (self-report of regular use). To date, dosimetry has yet to be implemented in PLD and cell phones. Truly though, even objective dosimetry measures would be of limited value without demonstrating a dose-effect relationship.
To assess the risk of hearing loss from PMS, Kumar et al .  selected 70 young adult participants who had used PMS for at least two years. The authors documented their subjects' chosen listening levels in quiet and in moderate levels of background noise deemed relevant to an individual's typical listening environment. They chose a bus noise at 65 dB SPL based on sound level measurements of the bus traveling at 40 km/hour. It is presumed (as it was not stated in the paper) that there was no multitalker speech also introduced in the background noise. This may be due to cultural differences-in many western countries, people often talk over the ambient noise, thus increasing the level of the "noise" of the PLD user's listening environment. Nevertheless, the authors showed chosen levels averaging 73-79 dB(A), depending on the device that the subjects used. There was no effect of an increased chosen listening level when background noise was introduced. While being noted but not controlled for in the analyses, all subjects used some type of insert earphone that was reported to provide some sound isolation from the ambient noise.
Overall, both experimental group (regardless of their chosen listening levels) and a control group had normal pure-tone thresholds and normal oto-acoustic emissions. On closer inspection of the data, the authors showed a significant correlation between increased pure-tone thresholds at 6000 Hz in both ears and estimated eight-hour equivalent exposures > 80 dB(A). Likewise, they found decreased DPOAEs in the high frequencies in both ears were correlated with Leq, 8 hn > 80 dB(A). Despite the barriers to successfully showing an effect on cochlear function, Kumar et al.  (and others before , ) showed a significant correlation between PLD listening behavior and auditory function.
Are these minute elevations in pure-tone threshold clinically relevant? Are the subtle reductions in OAEs clinically relevant? Absolutely not! To note, according to ISO 1999,  the median NIPTS reaches a clinically significant change after ten years of exposure to 90 dB(A) Leq, 8 hn (greater than a ten dB shift at 4000 Hz). The fact that the authors of this July Noise and Health paper succeeded in showing any relationship (despite the small sample size and combining all subjects with exposure greater than 80 dB(A) Leq, 8 hn) is quite astonishing (and concerning).
While on the topic of discovering immediate relevance to satisfy the media and critics, let us discuss the focus on reporting mean and median data. As has been described in all legitimate papers on hearing loss risk from PLD, the average PLD user is not at risk for NIHL. But why should we focus on the average? Should we fail to act on initiating efficacious hearing health interventions unless half the population has a handicapping NIHL? Most health care does not focus on the average person; the average person is healthy. Many definitions of "disease" consider function that is poorer than two standard deviations (SD) beyond the mean; sometimes, disease is not considered present until it is three SD from the mean. This represents 5 and 1% of a normally-distributed population, respectively. Williams  reported a SD on the order of 8-10 dB in his subjects' chosen listening levels and exposure estimates. A large SD requires large sample sizes to investigate the tails of the normal distribution. To date, the largest sample size providing estimated sound exposure is 350,  with most studies having far fewer than 100 subjects. Despite this, most studies have shown some individuals at risk (as Kumar et al .  showed).
Forty years after our 13 year-old boy received his first PLD, at age 53, when he is at the height of his earnings potential, will his hearing present a barrier socially or occupationally? He stands to work another 10-15 years before retirement, possibly longer given the present economy. Will his hearing support an active, productive lifestyle?
Perhaps this 13 year-old's behavior will change in his mid 20's, and his passion for music will shift to interest in work and/or family. At the age of 23, after ten years of music exposure, are his pure-tone thresholds normal? Are they as good as one would expect in a 23 year-old or has he developed some degree of NIPTS, essentially prematurely aging his ears?  Even if his hearing is normal, there is some evidence that early noise exposure leads to earlier onset presbycusis. 
Grants tend to run in fairly short cycles (a few years at most) and the public's attention wanes quickly if the researcher fails to show immediate relevance to the individual viewer. Ten years is a short time in an individual's lifespan, yet it is longer than practical for most longitudinal studies of hearing health risk. Cross-sectional studies are the next best option, except PLD is not the only hearing health risk that might contribute to NIPTS, so obtaining a large "clean" sample will be exceedingly difficult. So it is likely the debate will continue far longer than another ten years. As stated in the 2008 report on potential health risks from PLD by the European Union Scientific Committee on Emerging and Newly Identified Health Risks,  there is considerable lack of data regarding current PLD use patterns and whether or not PLD will have a long-term detrimental effect on hearing. Their very strict interpretation of risk (recommended exposure level limited to http://www.childrenshospital.org/MusiciansHearingProgram " www.childrenshospital.org/MusiciansHearingProgram) that these patients not provide additional proof that PLD can cause NIHL.
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