On 30 July 2004, members of Deafness Forum were emailed a discussion paper titled, Noise-induced (or noise injury) hearing impairment and hearing disorders: prevention through education”for comment by members of the forum. The original version circulated the day before had been extensively modified, with the clear intent of either broadening the discussion, or alternately restricting the discussion beyond the original concept put forward by the original author (Mr. Bill Hick).
From one point of view the original version placed undue emphasis on the work of one investigator, directly naming me or my work twice in the 2 page document and my work with Dr. Narelle Murray or citations of it no less than 13 times in the 1 page attachment. Such direct citing of a person or their opinions is unusual in discussion papers. Rather a full set of work and opinions is usually required to show an impartial account of all the work in the area, justifying the purpose of interest by Deafness Forum.
What the revised version achieved, on the other hand, was to deflect the debate away from our work, and in my opinion, by doing so, the point of introducing the debate to Deafness Forum was lost. I have submitted my response to Deafness Forum (below), firstly to supply the best references to our work, and to make available the key articles quoted in the original submission so that Forum and other members can assess the research for themselves.
LePage response to “POLICY DISCUSSION PAPER: Noise-induced (or noise injury) hearing impairment and hearing disorders: prevention through education.”
(also available as a pdf file)
Eric L. LePage, Ph.D.
Senior Research Scientist at NAL (1989-Sept. 2004)
38 Waratah Parade, Narraweena, 2099
Phone: 02 9982 9452;
Mobile: 0412 014 475
The understanding of noise-induced hearing loss has globally progressed considerably beyond treating noise exposure in isolation, and therefore regarding the education of attitudes to noise likewise. The original submission drew attention to our considerable work in the area at NAL (the Hearing Loss Prevention section). It was replaced with a version which rightly did not place undue emphasis on the work of any particular research effort. It is very important to this forum discussion to analyse why the original submission was replaced. This response is structured to explain that in order to make adequate progress on the topic it is essential to consider the factors (primarily the two main schools of thought). More importantly, the original submission did not make a sufficiently clear distinction between my prediction and any subsequent monitoring of new figures for hearing loss in the Australian population. As we have collected more data, the otoacoustic emission picture has not changed — the emission levels of young adults appear too low relative to surrounding age groups. The technical reasons for our confidence in this result are beyond the scope of this submission.
The changing demographic of noise-effects
In the15 years at NAL I have been collaborating with Dr. Narelle Murray, our data has led us to question the possibility of a steep rise in the prevalence of young people with premature hearing loss. Our predictions, stemming from otoacoustic emission (OAE) data, were based upon two outcomes: an unexplained dip the value of OAE strengths in cross-sectional data such that young adults had lower values relative to older adults (Murray, LePage and Tran, 1994), and a computer model (LePage, 1994) subject to a set of reasonable assumptions, which translated that dip into the future prevalence of hearing loss in the Australian population.
Since such a dip had never been seen in audiometric thresholds it tended to suggest two explanations. Firstly, that click-evoked otoacoustic emissions had some unexplained property which yielded a false trend with age, or secondly that the otoacoustic emissions were a more sensitive measure of hidden damage than thresholds. If the first were true, we had to work harder in understanding the OAE technique. If the second were true, then emissions were displaying early-warning properties which might be useful for prevention of hearing loss, in line with general principles of preventive medicine. We went on to show that in a population of nearly a thousand normal hearing adults, otoacoustic emission measures obtained by the same method could clearly separate groups with differing types and levels of noise exposure (LePage and Murray, 1998). While both sets of results were interesting, if not entirely convincing from a scientific point of view (stemming from the first explanation), taken together they did give us confidence that otoacoustic emissions may be a valuable adjunct to the traditional “block the noise” prevention message. An objective computer display has the potential to be more convincing than the educational programs of the past by virtue of disallowing individuals to say, “it will not happen to me” after they have been identified as being at greater risk.
The diagnostic correlate is rather akin to the objective ocular pressure test to look for early warning signs of glaucoma. Accordingly, this work has drawn quite wide interest from audiologists, medical practitioners and consulting acousticians. Since 1994 it has attracted hundreds of media reports, which unfortunately tended to sensationalise the results of the computer model. The author of the discussion paper showed awareness of the possibilities of stemming any such “epidemic” through the use of our early warning approach as an adjunct to education, and called for more concerted attempts to stem any predicted epidemic in hearing loss using education enhanced by our approach. I feel the approach deserves far more effort at validation than it has received so far.
Evaluating the need for action
If governments are to act to stem an “epidemic” of hearing loss, they must be convinced firstly that such an epidemic exists, and secondly that doing so is acting in the interests of the public purse in the short- to medium-term. Unfortunately such publicity seldom contains enough of the essential detail of the work reported, and, in this instance, the nature of emission strength and the assumptions of the computer model.
My 1994 prediction, based instead upon cross-sectional data provided figures for increase in hearing loss by the turn of the century, then after periods of ten and twenty years. The predicted increases were sufficiently marked so that audiologists over the country should be registering the trend.
Our work in recent years has been aimed at achieving scientific validation of the trend using longitudinal data. Accordingly, we have been following a cohort of people and setting out to show if those with lower emission levels, on average, develop a hearing loss sooner than those with high level emissions. Members of our cohort have been retained in our data pool now for over 12 years, so this has been an important study.
The global evidence of an increase in the prevalence of noise-induced hearing loss in young people is becoming clear (e.g. Niskar et al, 1998; 2001), and there has been considerable interest in our assertions internationally (e.g. OAE Portal). In Australia, it seems many professionals have been sufficiently convinced about our cross-sectional data that otoacoustic emissions do offer early warning of hearing threshold shifts, for it to have led to the inclusion of the approach in the current Australian Standard AS/NZS 1269.4.
How much evidence is necessary for government action?
My contribution to this discussion is directed at the pressing need to pursue my work on verifying those predictions and indeed, to consider the current proposal whether it is reasonable NOT to wait to act, before such a verification process is fully complete. In this respect the stage is not unlike the early stages of establishing links between smoking, lung cancer and cardiovascular disease. Long after the evidence was convincing enough for many people to begin action, savage academic debates raged as to the statistical adequacy of the claims for the existence of such a link in order to provide sufficient justification to begin action.
The long-term breakthroughs must come from biomedical research; a view strongly supported by Prof. Donald Henderson, at CUNY, Buffalo, NY, keynote speaker for our NAL Colloquium (see NAL Annual report 2002). These will take the form of genetically engineering fixes to outer hair cell damage, and understanding the trauma processes which lead to permanent damage (see brief review LePage, 2003). Such research may be more academic in its pursuit, because it is setting out to treat the problem of hearing loss from a far more holistic point of view. There is substantial evidence that a large percentage of early hearing loss cases, however widespread, possess a genetic origin, which makes certain individuals more susceptible than others. Our research program is well on the way to utilising otoacoustic emission technology to measuring individual susceptibility. Whatever the genetic component, noise exposure is a strong component and we at NAL have been optimistically pursuing simple measures of that susceptibility. Alas, an intellectual and experimental exercise of the magnitude of our research program cannot be measured in terms of milestones met by a certain date.
The risk factors for hearing loss go far beyond exposure to noise, and in my reading of the literature, are as at least as important as noise exposure. The long history of hearing loss in the work place has amply demonstrated a strong reluctance on the part of industry to spend dollars on prevention. It is far easier for an employer to outsource the responsibility of hearing loss in workers or to pay compensation in the case of extreme hearing loss. If otoacoustic emission research is not currently finding favour, it is clearly because it raises very large issues and does so in terms which are foreign to the practice of audiology. It remains, for me the most exciting development ever introduced into clinical practice.
R&D vs holistic approach?
There is intention that NAL will pursue viable prevention projects which reduces sound trauma through practical research and development using advanced digital technology. NAL has derived great commercial benefit from the marketing of the acoustic shock protector for use by telephonists to reduce exposure to impact noise in headsets.
My main response for discussion by Deafness Forum is to introduce three questions:
- Is there still a place for Australian Research into prevention via a continuing and thorough evaluation of early-warning methodology using otoacoustic emissions (the point of introducing it into the Standard) ?
- Modern biological research has shown the inadequacy of treating noise trauma in isolation. If Australia has a cutting edge in our new approach, how can that be restored ?
- How likely is it that commercial organisations will fund this work, and if not, who will ?
I assert that support for prevention research needs to continue to come from the highest levels of government as obligatory service to the community simply because it needs to be made on the basis of ongoing social cost measured at least in financial terms and it needs continuous funding independent of commercial forces.
Hearing loss in males is a significant social problem. We have observed that 95% of inmates in NSW prisons are men, and on average, their emission strengths place their hearing at least a decade older than individuals the same age in the general population (Murray, LePage and Butler, 2004). Moreover, it has been claimed that in the USA a population of males the size of San Francisco is in prison. The otoacoustic emission levels of males is generally lower than females and we pointed that out to the Inquiry into the Education of Boys (LePage and Murray 2001). By my estimation about 0.01% of this country’s expenditure on hearing aids and/or prisons, would promote an adequate evaluation of hearing in primary school children.
The Discussion Paper produced by Deafness Forum on noise-induced hearing loss is timely particularly because an important research program has just been extinguished for reasons which might more appropriately have been debated in such a Forum before the decision was taken. The other view of waiting for overseas confirmation of our identified trend before acting is that yet again, Australian research “misses the boat”.
Our claims are:
- there is an epidemic on the way which will primarily affect men, in much larger numbers of individuals than workers in telephone exchanges, and
- the potential impact of our early warning approach requires to be fully evaluated with significant resources;
- early warning estimates are expected to be an important component of any education program, which should be fully functional in the early years of schooling. As observed forcefully by Rose, such an education process needs to be repeated often to have much impact.
- Australian Standard. Auditory Assessment. AS/NZS 1269.4 : 2004 Occupational Noise Management.
- LePage, E. L. (1994). Model forecasting the prevalence in hearing loss in the Australian population over the next 20 years based on trends in decline in otoacoustic emission strength. In: Better Hearing Australia conference. Better Hearing Australia.
- LePage, E. L. (2003). Scope of otoacoustic emissions for assessment and prevention: past, present and future. Audiology Now. (Audiological Society of Australia). (Spring issue).
- LePage, E. L., Murray, N. M., & Seymour, J. D. (2004). Early-warning of hearing loss using click-evoked otoacoustic emissions: results of a cross-sectional analysis. Noise and Health. (Submitted for publication).
- LePage, E. L., & Murray, N. M. (1993). Click-evoked otoacoustic emissions: comparing emission strengths with pure tone audiometric thresholds. Aust.J.Audiol. 15 , 9-22.
- LePage, E. L., & Murray, N. M. (1998). Latent cochlear damage in personal stereo users: a study based on click- evoked otoacoustic emissions. Med J Aust 169(11-12), 588-92.
- LePage, E. L., & Murray, N. M. (2000). House of representatives standing committee on employment, education and workplace relations: Education of boys. Tuesday, 14 November 2000. EEWR415-EEWR427. Commonwealth of Australia: Official Committee Hansard,(pdf p35-47).
- Murray, N. M., LePage, E. L., & Butler, T. (2004). Hearing health of NSW prison inmates. ANZ J. Public Health, (Accepted for Publication).
- Murray, N. M., & LePage, E. L. (1993). Age dependence of otoacoustic emissions and apparent rates of ageing of the inner in an Australian population. Aust.J.Audiol., 15(2), 59-70.
- Murray, N. M., & LePage, E. L. (submitted for publication). Ageing effect in click-evoked otoacoustic emissions and pure tone audiometry in groups with different types of noise-exposure. Noise and Health.
- Niskar, A. S., Kieszak, S. M., Holmes, A. E., Esteban, E., Rubin, C., & Brody, D. J. (2001). Estimated prevalence of noise-induced hearing threshold shifts among children 6 to 19 years of age: the Third National Health and Nutrition Examination Survey, 1988-1994, United States. Pediatrics 108(1), 40-3.
- Niskar, A. S., Kieszak, S. M., Holmes, A., Esteban, E., Rubin, C., & Brody, D. J. (1998). Prevalence of hearing loss among children 6 to 19 years of age: the Third National Health and Nutrition Examination Survey. JAMA 279(14), 1071-5.
- Rose, G. (1981). Strategy of prevention: lessons from cardiovascular disease. British Medical Journal 282, 1847-1851.
- Rose, G. (1985). Sick individuals and sick populations. Intl. J. Epidemiology 14, 32-38.
- Williams, W., Purdy, S. C., Murray, N. M., Dillon, H. A., LePage, E. L., Challinor, K., & Storey, L. Does the presentation of audiometric test data have a positive effect on the perceptions of workplace noise and noise exposure avoidance? Noise and Health (Submitted for publication).
- Kemp, D. T. (2003). The OAE Story: An illustrated history of OAE research and applications through the first 25 years. Hatsfield, Herts., U.K.: Otodynamics Ltd.
- LePage, E. and Murray, N., (1996). A new approach to hearing loss prevention. NAL Researh & Development Annual Report 1995/96, 25-30.
- LePage, E. L. (1998). Occupational Noise-Induced Hearing Loss: Origin, Characterisation and Prevention. Acoust.Aust., 26(2), 57-61.
- LePage, E. L. (2004). Scope of otoacoustic emissions for assessment and prevention: past, present and future. Audiology Now (Journal of the Audiological Society of Australia), (Spring issue).
- LePage, E. L., Murray, N. M., Tran, K., & Harrap, M. J. (1993). The ear as an acoustical generator: otoacoustic emissions and their diagnostic potential. Acoustics Australia, 21(3), 86-90.
- LePage, E. L., Murray, N. M., & Tran, K. Comparison of otoacoustic emission measures of cochlear damage in the Australian population with hearing loss in the Australian and British populations. In: Better Hearing Australia conference. Better Hearing Australia.
- LePage, E., Murray, N. M., and Tran, K., (1993). Normative click-evoked otoacoustic emission data and their relationship to pure tone audiometry. NAL Research & Development Annual Report 1992/93., 18-19.
- LePage, E., Murray, N., and Butler, T., (2001). The scope of non-noise factors influencing research aimed at the effects of noise: one example blood cholesterol level. NAL Research & Development Annual Report 2000/2001, 17-20.
- Lucertini, M., Moleti, A., & Sisto, R. (2002). On the detection of early cochlear damage by otoacoustic emission analysis. J Acoust Soc Am 111(2), 972-8.
- Maison, S. F., & Liberman, M. C. (2000). Predicting vulnerability to acoustic injury with a noninvasive assay of olivocochlear reflex strength. J Neurosci 20(12), 4701-7.
- Marshall, L., & Heller, L. M. (1998). Transient-evoked otoacoustic emissions as a measure of noise-induced threshold shift. J Speech Lang Hear Res, 41(6), 1319-34.
- Murray, N. M., LePage, E. L., & Mikl, K. A longitudinal study of cochlear damage and hearing in an orchestra tested with click-evoked otoacoustic emissions and pure tone audiometry. Noise-Effects ’98 (pp. 82-85). Sydney.
- Murray, N. M., LePage, E. L., & Tran, K. Ageing characteristics of the Australian population in terms of otoacoustic emission strengths: global and individual picture. In: Better Hearing Australia conference. Better Hearing Australia.