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

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Health risks from exposure to noise from personal music playersgraders with hearing loss has increased by 2.8 times, and eighth graders had an increaseof 4 times (Montgomery and Fujikawa, 1992). Danish children starting school in 1977,1987 and 1997 were evaluated for hearing ability by a review of 1,605 school healthrecords (Gissel et al. 2002). Higher prevalence of impaired hearing ability in children whostarted school in 1987 and 1997 compared to those who started school in 1977 wasfound; in addition at the end of school year group 1977 hearing had become as poor asthat of year group 1987. Reduced hearing was typically at high frequencies, indicating tonoise-induced hearing impairment (Gissel et al. 2002).Boys and girls (aged 14–17 years) were examined during a four-year period.Audiological, psychosocial, and sound measurements were performed yearly todetermine the hearing threshold level (HTL) of participants in the 250–16.000 Hz range,their participation in recreational activities, and the sound levels at discos and throughpersonal music player use. A tendency of the mean HTL to increase in both gendersduring the study was observed, especially at 14.000 Hz and 16.000 Hz. Boys had ahigher mean HTL than girls. The participation in musical activities increased yearly,"attendance at discos" being the favourite musical activity for both groups. In general,boys were more exposed to high sound levels than girls. In this 4-year longitudinal studyit was concluded that the exposure to high sound levels during leisure activities (but notnecessarily from PMP) could be a cause of permanent hearing damage among youngpeople with “tender ears” (Biassoni et al. 2005).Although epidemiological literature data does not support the view that there is widespreadhearing loss caused by exposure to amplified music in young people under theage of 21 years, some authors stress that if the recreational pattern remains the same,there could be some risk of noise-induced hearing loss by the age of mid-twenties(Carter et al. 1982). Slight alterations of hearing function have been detected as possibleearly signs of ear impairment before deficits were detected with classical audiometry byfrequency selectivity and high definition audiometry (West and Evans 1990, Meyer-Bisch1996), otoacoustic emissions (LePage and Murray 1998) and very high frequencyaudiometry (Peng et al. 2007). However no follow-up data is available for these studies.3.8.2. Hearing threshold shiftIn the population with increased risk of hearing impairment from personal music playerseither temporary hearing threshold shift (TTS) or permanent hearing threshold shift(PTS) may develop. TTS may result from short (few hours) exposures at the levels nearthe maximum output of the music device. PTS may result from repeated exposures (overyears) to moderate sound levels exceeding allowable dose of noise.3.8.2.1. Temporary threshold shift (TTS)Only few studies have been published on temporary hearing threshold shift due to musicsounds from personal music players. They were mainly laboratory investigations on thehealthy volunteers overexposed to sounds.In a pilot study by Lee et al. 16 volunteers listened to headphone sets for 3 hours at theirusual maximum level. Six of them showed TTS of 10 dB at one or more audiometricfrequencies, and one volunteer showed a TTS of approximately 30 dB at 4 kHz. Theseshifts returned to normal within 24 hours in all individuals. The average post-test musicsound level ranged from 94 to 104 dB SPL (Lee et al. 1985).In the study by Turunen-Rise et al. the TTS was measured in 6 volunteers with normalhearing (3 males and 3 females aged 23-40 years). They were exposed for 1h to popmusic (that generated the highest noise level among all types of music tested) at thegain setting of 8 on the scale. Corresponding field levels of music sound ranged from 85to 95 dB(A). A small notch at 4 kHz (2-3 dB on average, no more than 15 dB) wasobserved after exposure to pop music with moderate use of percussion instruments,while significantly more TTS was observed with the pop music extensively usingpercussion instruments. The highest exposures produced greatest TTS. Hearing50
Health risks from exposure to noise from personal music playersimpairment recovered completely within 20-40 min. for the majority of subjects(Turunen-Rise et al. 1991).In the study by Loth et al (1992), 12 volunteers listened to two recordings (classicalmusic and hard rock) at an acoustic level complying with safety regulation. TTS at 4 and6 kHz were measures just after exposure and it was, on the average 5 dB. No differencebetween frequencies and type of music was found.3.8.2.2. Permanent threshold shift (PTS)Permanent threshold shift that could be related to music players was investigated byseveral authors in the field studies designs. Both, positive and negative findings werepublished.The first study evaluating the potentially harmful effects of amplified music on youngpeople’s hearing was published in early 80’s of 20 th Century, and failed to prove hearingimpairment (Carter et al. 1982).In their study Wong et al. (1990) assessed the prevalence of use of personal cassetteplayers among youths in a residential community in Hong Kong. They interviewed 487individuals aged 15-24 years, with 394 (81%) reported using PCP regularly (i.e. for 3days or more in a week for at least 6 months). The mean duration of PCP use was 2.8years, and the mean listening time was 4.5 hours per week. Among the 78 PCP users and25 non-users examined with pure-tone audiometry, no significant difference in the meanhearing threshold was observed for the frequencies tested (250–8000 Hz). However inthe studied group, only four subjects were habitually exposed to sound levels higher than85 dB(A). One was exposed to 116 dB(A) and was found to have a 4000 Hz dip on hisaudiogram. The authors conclude that despite the high prevalence of PCP use, mostyouths used their PCP at relatively safe sound levels with low risk of hearing loss (Wonget al. 1990).Similar results were obtained by Kawada et al in 1990 and West et al. (1990). In the firststudy no significant differences between mean hearing acuity between PMP users andnon-users were found in 155 medical students aged between 22-29 years. However, themean hearing acuity at 4 kHz showed a tendency of being lower in users than non-users,and higher percent of individuals with hearing impairment was found in the user group ascompared to the control. The authors suggest that 10% of the young generation is at riskfor permanent hearing loss from use of portable music players (Kawada et al. 1990). Inthe second paper, sixty subjects in the 15-23 age range were examined. While the mostexposed groups did not show significantly greater averaged thresholds, there was asignificantly increased prevalence of notches in the 3.5-6 kHz audiograms of the olderage group (West, 1990).The concern about safety of PMPs arose after publication of the study by Meyer-Bisch(1996). The investigation involved young people 14-18 years who were just discoveringmusic played loudly. Three subgroups were defined for users of personal cassetteplayers: occasional, 2-7 h/week and >7 h/week. High definition audiometry (449frequencies over the spectrum from 125 to 16000 Hz) was applied and early warningindicator (EWI) was calculated from the arithmetic average of the thresholds at 3, 4 and6 kHz. The groups were matched according to disco attendance, PCP use and concertattendance. PCP users were defined as those who never or only occasionally go torock/variety concerts or discotheques, but who use a PCP for at least 2 h/week. In total249 individuals from 14-30 years of age (mean 17.7) were assessed including 54individuals (21.7%) with the use of a PMPs for at least 8 h/week (majority of them were15-16 years old subgroup). A statistically significant increase of average hearingthresholds was found in people using PMPs > 7 h/week (54 subjects) as compared tothose using PCP 2–7 h/week (195 subjects) and as compared to their matched control.The differences were significant at the range of frequencies from 2 to 12 kHz. From thesame study of Meyer-Bisch, it could be concluded that only the individuals with high rateof using PMPs (more than 7 h/week) develop significant permanent threshold shift. On51
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