Potential health risks of exposure to noise from personal music ...

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Health risks from exposure to noise from personal music players3.4.5. ConclusionsHearing impairment may be defined as a reduction in hearing acuity or sensitivity, ortinnitus. Hearing loss is the inability of the affected individual to hear sounds at certainlevels that can be measured with pure-tone audiometry. According to the WHO Grades ofhearing loss no or very slight hearing problems exist when hearing threshold in thebetter ear is at or below 25 dB.The reduction in hearing acuity results in the impairment of speech understanding.High-frequency hearing loss, which is typical for age and noise-related hearingimpairments may result in worsening speech-in-noise comprehension. It is on average by1.2 dB per 10 dB. The ability to understand speech may be also impaired despite anormal audiometric threshold due to loss of timing information.Tinnitus defined as “a phantom perception of sound" is a common problem. It is usuallyoriginating within the auditory system and is caused by abnormal conditions in thecochlea, the cochlear nerve, the ascending auditory pathway, or the auditory cortex.Hearing ability deteriorates with increasing age in virtually all people and thisdeterioration accelerates for older people. In young adults, up to the age of 40, thisprocess is slow and leads to negligible levels of hearing impairment.3.5. Noise-induced hearing loss and associated impairmentsNoise-induced hearing loss (NIHL) accrues progressively and often unnoticed until it hasreached a certain degree. The main site of impairment is the outer hair cells of thecochlea, where the damage is irreversible (Bamiou and Lutman 2007). Very high levels ofnoise exposure can lead to acute mechanical damage to inner and outer hair cells, butthis form of damage is very rare. More commonly, there is chronic damage that builds upslowly over time. Since noise-induced hearing loss is irreversible, the main form oftreatment is prevention.3.5.1. Epidemiology of noise-induced hearing lossExposure to excessive noise is one major cause of hearing disorders worldwide. TheWord Health Organization programme for Prevention of Deafness and HearingImpairment (WHO 1997, Smith 1998) stated: "Exposure to excessive noise is the majoravoidable cause of permanent hearing impairment worldwide. Noise-induced hearing lossis the most prevalent irreversible industrial disease, and the biggest compensatableoccupational hazard. More research is needed on basic mechanisms and means ofprevention". In a more recent report WHO states (WHO 2002, Nelson 2005) “Worldwide,16% of the disabling hearing loss in adults is attributed to occupational noise, rangingfrom 7% to 21% in the various subregions”. Surveys estimate that noise-induced hearingloss (NIHL) affects 10 to 15 million people in the USA (see Lynch and Kil 2005). In theUK (Palmer et al 2002b) showed that some about 180,000 people aged 35-64 years wereestimated to have severe hearing difficulties attributable to noise at work and for tinnitusthis increased to 350,000 people who were seriously affected. In France a survey by theministry of employment (Sumer: surveillance médicale des risques professionnels 2003,Magaud-Camus 2005) indicates that approximately 7% of employed workers are exposedto excessive noise levels (more than 85 dB(A) for at least 20 hours per week) and about25 % are exposed to hazardous noise exposures (more than 85 dB(A) but less than 20hours per week); most exposed workers belong to industry (18%) and, to agricultureand house building (12%). Legally acceptable levels of noise exposure were definedmany years ago taking into account the two main physical parameters of acousticintensity and duration of exposure as used for reference above.In order to better counteract NIHL a European directive that took effect in February2006, lowered the first action level (provide protection) to 80 dB(A) (Directive2003/10/EC, 2003). Acute acoustic trauma from firearms is the most frequent pathology26
Health risks from exposure to noise from personal music playersobserved in the French army and unfortunately its prevalence increased by about 20percent in 2006 (BS EN ISO 389-2:1997, 2006).Although early reviews concluded that leisure noise was unlikely to be a significant threatto hearing compared to occupational noise (e.g. MRC 1986), they noted a need for moregood data and research. Since then there have been significant changes in the patternsof noise exposure. Smith et al. (2000) found that the numbers of young people withsocial noise exposure had tripled (to around 19%) since the early 1980s, whilstoccupational noise had decreased.This increase of risk is consistent with a recent study by Niskar et al (2001), whoestimated the prevalence of noise-induced hearing threshold shift among children aged6-19 years in the third national health and nutrition examination survey of 1988-1994 inthe USA. They found that 12.5% had noise-induced threshold shift (NITS) in one or bothears, with higher prevalence in boys (14.2%) compared to girls (10.1%), and in olderchildren aged 12-19 (15.5%) compared to 6-11 year olds (8.5%). 6kHz was the mostaffected frequency (77.1%) compared to 4 kHz (23.8%) and 3 kHz (14.1%). A singlefrequency was involved in 88.4% of children. Among children meeting NITS criteria14.6% had a noise notch for both ears. No equivalent data exist yet on the Europeanpopulation. In the earlier studies (Davis 1989, Davis 1995, Smith et al 2000) there wasno evidence of such notches in 18-25 year old individuals in the UK.3.5.2. Environmental noise exposure levelsIn industry settings, the noise levels can average up to 90-125 dB in several areas ofwork. Outside the workplace, a high risk of hearing impairment arises from attendingdiscos and rock concerts, exercising noisy sports (hunting, sports shooting, speedway) orfrom exposures to military noise. Children could be exposed to noisy toys as trumpets(92–125 dB SPL), whistles (107-129 dB SPL) and toy weapons (113- >135 dB SPL)(Plontke et al. 2004).By their leisure activities individuals expose themselves to noise sources includingpersonal music players which usually generate sounds across a broad frequency rangeand reaching high sound pressure levels. The equivalent sound levels in discos rangefrom 104.3 to 112.4 dB(A), compared to 75 to 105 dB(A) from personal music players(Serra et al. 2005). The noise dose measures over 4 hours showed an L aeq of 104.3 dB.The nightclubs' average sound level ranged between 93.2 to 109.7 dB(A). Sounds otherthan noise (such as music) can, at high acoustic levels, be as dangerous for hearing asindustrial noise.There seems to be a trend for increased distribution and use of PMPs, and their improvedtechnical qualities allow for playback without distortion at high levels.Environmental noise like traffic noise, aircraft noise, construction noise or neighbourhoodnoise, although sometimes very annoying, does not reach the equivalent levels that canbe harmful to hearing. On the other hand, these sources of noise can cause non-auditoryeffects.3.5.3. Exposure – effect relationshipAs it was usefully summarised by Lutman et al. (2008), knowledge concerning therelationship between noise exposure and NIHL is based on cross-sectional studies ofpeople exposed to noise, much of which was conducted several decades ago and whichconcentrated on people exposed continuously to high levels of noise that were morecommonplace in the 1950’s and 1960’s. This knowledge is far from complete. Moststudies have suffered from the lack of appropriate non-exposed control subjects andlongitudinal studies are almost entirely lacking (Lutman and Davis 1996). Authoritativereports have involved large primary studies or have synthesised data from several largeprimary studies. The seminal study of Burns and Robinson (1970) has been influential inthe UK and elsewhere. It formed the basis of the first edition of the international27
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