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|Year : 2014
: 16 | Issue : 72 | Page
|Hearing and loud music exposure in 14-15 years old adolescents
Mario R Serra1, Ester C Biassoni1, María Hinalaf1, Mónica Abraham1, Marta Pavlik1, Jorge Pérez Villalobo1, Carlos Curet2, Silvia Joekes3, María R Yacci3, Andrea Righetti3
1 Centre for Research and Transfer in Acoustics (CINTRA), Unit Associated of CONICET, National Technological University (UTN), Cordoba Regional Faculty, Cordoba, Argentina
2 High Otorhinolaryngological Technology Center. Forming Center for Otorhinolaryngology Specialists, National University of Cordoba, Cordoba, Argentina
3 Institute of Statistics and Demography , National University of Cordoba, Cordoba, Argentina
Click here for correspondence address
|Date of Web Publication||10-Sep-2014|
Adolescent exposure to loud music has become a social and health problem whose study demands a holistic approach. The aims of the current study are:
(1) To detect early noise-induced hearing loss among adolescents and establish its relationship with their participation in musical recreational activities and (2) to determine sound immission levels in nightclubs and personal music players (PMPs).
The participants consisted in 172 14-15 years old adolescents from a technical high school. Conventional and extended high frequency audiometry, transient evoked otoacoustic emissions and questionnaire on recreational habits were administered. Hearing threshold levels (HTLs) were classified as: normal (Group 1), slightly shifted (Group 2), and significantly shifted (Group 3). The musical general exposure (MGE), from participation in recreational musical activities, was categorized in low, moderate, and high exposure. The results revealed an increase of HTL in Group 2 compared with Group 1 (P < 0.01), in Group 3 compared with Group 2 (P < 0.05) only in extended high frequency range, in Group 3 compared with Group 1 (P < 0.01). Besides, a decrease in mean global amplitude, reproducibility and in frequencies amplitude in Group 2 compared with Group 1 (P < 0.05) and in Group 3 compared with Group 1 (P < 0.05). A significant difference (P < 0.05) was found in Group 1's HTL between low and high exposure, showing higher HTL in high exposure. The sound immission measured in nightclubs (107.8-112.2) dBA and PMPs (82.9-104.6) dBA revealed sound levels risky for hearing health according to exposure times. It demonstrates the need to implement preventive and hearing health promoting actions in adolescents.
Keywords: Adolescents, hearing conservation, loud music exposure, noise induced hearing loss
|How to cite this article:|
Serra MR, Biassoni EC, Hinalaf M, Abraham M, Pavlik M, Villalobo JP, Curet C, Joekes S, Yacci MR, Righetti A. Hearing and loud music exposure in 14-15 years old adolescents. Noise Health 2014;16:320-30
|How to cite this URL:|
Serra MR, Biassoni EC, Hinalaf M, Abraham M, Pavlik M, Villalobo JP, Curet C, Joekes S, Yacci MR, Righetti A. Hearing and loud music exposure in 14-15 years old adolescents. Noise Health [serial online] 2014 [cited 2020 Dec 1];16:320-30. Available from: https://www.noiseandhealth.org/text.asp?2014/16/72/320/140512
| Introduction|| |
Over the last years, an increasing exposure to noise has been observed outside the workplace during leisure time activities, which is suspected to increase one's risk of noise-induced hearing loss (NIHL), particularly in adolescents and young people. ,, Due to the ever-increasing intensity levels at live concerts and nightclubs, and to the appearance of new personal music devices, exposure to loud music has become the most studied source of excessive sound exposure in children and youths in several countries. Thus, new products and organizations have been created with the aim of reducing hearing risks of overexposure to music. 
According to a document published by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHRs) of the European Commission:  "Exposure to excessive noise is a major cause of hearing disorders worldwide. It is attributed to occupational noise. Besides noise at the workplace, which may contribute to 16% of the disabling hearing loss in adults, loud sounds at leisure times may reach excessive levels, for instance in discos and when using personal music players (PMPs)." And the SCENIHR adds: "It is estimated that over two decades, the number of young people with social noise exposure has tripled (to around 19%) since the early 1980s, while occupational noise has decreased" (p.4).
There are hardly any regulations concerning recreational noise exposure, commonly related to music, which frequently exceeds sound pressure level limits established for occupational noise exposure. Such is the case of nightclubs where the sound pressure levels can easily exceed 100 dBA, which is thought to constitute a risk for hearing damage. , According to Morata,  the term "music-induced hearing loss" should be used instead of "NIHL." The World Health Organization  has warned about hearing loss as a consequence of excessive noise exposure, considering it one of the "most frequent irreversible illnesses," especially among young people, thus calling for actions addressed to its early diagnosis and prevention. Studies have reported tinnitus and temporary threshold shifts (TTSs) in teenagers after attending live concerts and nightclubs, as well as among those who are regular users of PMP. 
In general, the literature informs about cross-sectional hearing studies conducted on young people before and after being exposed to a musical event. This kind of study does not show what happens to hearing over time in the case of routine exposure to different sources of loud music during adolescence. The answer to this question can be found in longitudinal studies where changes over time can be observed. 
Hearing loss may be detected either by pure-tone audiometry quantifying overall hearing loss or otoacoustic emissions (OAEs) detecting cochlear status where hearing loss caused by outer hair cells (OHCs)' dysfunction can be inferred. ,,,,, OAEs may be particularly useful for detecting NIHL since the OHC are known to be the most vulnerable elements of auditory processing with respect to noise overexposure. 
An interdisciplinary longitudinal study was conducted in Argentina in order to examine the effects of recreational noise exposure on adolescent hearing. The study included boys and girls (aged 14-17) from two private schools who were examined during a 4-year period by means of yearly audiological, psychosocial, and acoustic studies. ,,,, On the basis of those results, a program was designed this time with students from public technical schools belonging to lower social economic classes than students in the first stage,  since a high number of them will be prospective applicants for jobs in factories and industries. This program was designed to assess hearing, recreational habits, and sound exposure levels during adolescent entertainment activities at two moments of high school: 3 rd year (test) and 6 th year (retest).
The present article will present the results obtained by the adolescents in the test at the first school where the program was implemented.
The aims are:
- To detect early NIHL among adolescents and the relationship with their participation in musical recreational activities;
- To determine sound immission levels in nightclubs and PMPs.
| Materials and Methods|| |
With the consent of the Ministry of Education of Córdoba, this study was carried out with students from the biggest technical school in the city of Córdoba, Argentina.
The sample consisted of 188 male 3 rd year high school students ages 14-15 who had received their parents'/tutors' written informed consent to participate in the study.
The inclusion criteria for all participants were:
- Normal middle-ear function (pressure and compliance) by tympanometry
- Normal otoscopic examination.
Sixteen adolescents were excluded from the study for not meeting the above requirements to avoid potential effects on audiometry and transient evoked OAE (TEOAE) results.
The audiological assessment, conducted by audiologists, included:
- The administration of an Auditory State Questionnaire in order to learn about the medical history of their ears and hearing.
- An otoscopic examination to verify the condition of the ear canal and tympanic membrane.
- A tympanometry to determine the condition of the middle-ear.
- A standard audiometry in the conventional frequency range (250-8000) Hz and an extended high frequency audiometry (EHFA) (8000-16,000) Hz to determine hearing threshold level (HTL) within the audible spectrum, using the bracketing method specified by the ISO 8253 1:2010 standard. 
The test's signal level steps were fixed at 3 dB for HTL to be determined with greater precision than with traditional 5 dB steps, as well as to make it easier for students to answer than at the 2 dB fixed in the previous study. 
According to the HTL in both frequency ranges, three groups were established:
Group 1: With normal HTL (up to 18 dB) at all frequencies.
Group 2: With a slight shift of HTL (up to 24 dB) at least in one frequency.
Group 3: With a significant shift of HTL (superior to 24 dB) at least in one frequency.
Transient evoked OAEs to detect mechanical cochlear status. TEOAEs were evoked as follows:The stimulus was a nonlinear click, quick screen mode, the mean intensity of the stimulus was 80 dB pk, 260 presentations of click, the stability of the stimulus was maintained ≥80%, and the peak noise rejection level applied was 47.7 dB.
The presence of normal TEOAEs was determined by a whole reproducibility level ≥70%, and a signal-to-noise ratio ≥6 dB in three of the frequencies analyzed (1000, 1500, 2000, 3000, and 4000) Hz.
The audiological equipment included:
- A clinical otoscopy Heine, model Beta 100.
- An impedanciometro Kamplex Interacoustics, model MT 10.
- A digital audiometer Madsen, model Orbiter 922 DH/1, for both frequency ranges, whose calibration was controlled 3 times a year. In order to comply with the requirements of national and international standards with regards to measurement procedures, the audiometer calibration was carried out in the conventional range, according to ISO 389 1:1998 and IRAM 4075:1995 standards; , and in the extended high frequency, according to ISO 389-5:2006 standard,  using an artificial ear Brüel and Kjaer, type 415, equipped with a standard microphone, also B and K, type 4134, traceable to the reference standards of the European Community. 
- A set of supra-aural earphones Sennheiser, model HDA 200 for both audiometric ranges calibrated according to ISO 389 8:2004 standard  was used. The application force of the headband (10.3 N) complies with the specifications of ISO 389 5:2006 standard  (10.0 ± 1.0 N).
- OAE equipment, Otodynamics Ltd, model Echoport ILO 292 USB II. UGD TE and DPOAE Probe, provided by the equipment. ILO V6 OAE clinical analysis and data management software.
The audiological studies were conducted after approximately 10-12 h of auditory rest in the morning as adolescents were thought to have had auditory rest during the night. The audiological tests were carried out in an utilitarian vehicle adapted as a mobile audiometric booth, complying with the international ISO 8253-1:2010 and the national IRAM 4028-1:1992 standards , with regards to background sound levels of noise.  The audiological evaluation was conducted by audiologists in two sessions lasting approximately 20 min to avoid tiring the patients.
Participation in musical recreational activities assessment
An "Out-of-School Activities Questionnaire", an adaptation of the questionnaire employed at the Institute for Industrial Medicine and Hygiene at the Faculty of Medicine of Otto von Guericke University, Magdeburg, Germany,  was administered in order to establish in detail the different types of musical recreational activities adolescents engage in.
The questionnaire is composed of 42 questions. The analysis of this questionnaire revealed adolescent participation in five different music-related recreational activities:
- Exposure to music at home (EMH);
- Playing a musical instrument and being part of a musical group (PMI);
- Live concert attendance (LCA);
- Nightclub attendance (NA);
- Use of PMP (UPMP).
The questionnaire asks how often adolescents participate in each activity since when, the time dedicated to each, and the self-reported sound levels they are exposed to, thus obtaining a "participation level" for each activity (doesn't participate, low level, medium level, and high level). From the combination of participation levels in the five musical activities three categories of musical general exposure (MGE) are obtained:
- Low exposure to music, made up of doesn't participate and low level of participation in all recreational activities.
- Moderate exposure to music, composed of a medium level of participation in one or more recreational activities.
- High exposure to music that includes a high level of participation in one or more recreational activities.
The questionnaire was administered collectively and during school hours, with an emphasis on the fact that participation was voluntary. Administration of the survey was conducted by psychologists who provided detailed instructions about how to complete the survey, and students had the opportunity to ask questions. It lasted for approximately 20 min. Teachers remained in the classroom to help monitor the behavior of students.
Measurements of sound immission levels of nightclubs and PMPs, the most important adolescent musical recreational activities, were carried out.
Measurements at nightclubs
The measurements were carried out in the four nightclubs most frequently visited by the participants, according to their answers to the questionnaire.
In the case of nightclubs, a fundamental prerequisite for the assessment of the real sound situation in them is the possibility of carrying out measurements in a concealed way so as to avoid that the authorities reduce the level of the music.
The measurements were carried out using a concealed miniature instrument arrangement, implemented ad-hoc, especially for previous studies.  The acquisition system consisted in:
- A free field microphone Norsonic, type 1220.
- A microphone preamplifier Brüel and Kjaer, type 2639.
- A measuring amplifier Norsonic, type 336.
- A portable DAT recorder Sony, type TCD-D8.
- A sound source reference Brüel and Kjaer, type 4231.
The instruments chain was interconnected and calibrated in the laboratory. The whole equipment was installed in a small trendy backpack as those worn by adolescents, and it was prepared to work for about 4 h.
The measurements in situ were carried out by the adolescents participating in the study themselves under the supervision of a responsible selected adolescent. They attended the nightclub with the equipment, hidden in the small backpack, previously described, and they participated in all the activities of the place as any other adolescent. The measurements collected in situ were analyzed at the laboratory.
Measurements of personal music player
According to the answers to the questionnaire, the PMP most commonly used by the participants was MP3s equipped with headphones or earphones. The 10 adolescents who used MP3 most frequently and with the least precaution (taking into account the number of hours/day and sound level as assessed by themselves) were selected to participate in these measurements.
A measurement technique, based on the ISO 11904-2:2004 standard  (manikin-technique), using a head and torso simulator,  Brüel and Kjaer, type 4128 with normalized occluded ear  was used to measure the real sound levels in the ear of the adolescents. The sound pressure level measured by the ear simulator microphone represents the pressure found at eardrum.
To carry out the measurements, the participants had to bring their own portable musical devices, select three of their favorite songs, and listen to them at the volume they normally did. They were asked to retain the final setting made on the device when they finished listening. Using the same portable musical device the songs were reproduced on the artificial head and torso at the sound levels pre-set by the adolescents. The manikin measurements of sound pressure levels in the PMP (LMAeq) were converted to free-field equivalent sound level (LMFFAeq) according to ISO 11904-2:2004 standard. 
A Student's t-test was applied to analyze the significance of the difference between ears of audiometric and TEOAEs profiles. Then, a Student's t-test for independent samples was applied to analyze:
- The mean differences between audiometric groups;
- The amplitude and reproducibility between presence and absence of TEOAEs;
- The audiometric profiles between the presence and absence and low level of TEOAEs;
- The amplitude and reproducibility of TEOAEs between the audiometric groups.
Descriptive statistics of adolescent participation in musical recreational activities were obtained. Pearson's Chi-squared test was applied to analyze the association between the audiometric groups and the MGE.
The differences in audiometric profiles between MGE categories and in TEOAEs between MGE categories were analyzed using Student's test for independent samples.
The acoustic measurements were expressed in values of equivalent sound levels in A decibels (LAeq), in the case of nightclubs, and in manikin free-field equivalent sound level in A decibels (LMFFAeq), for the MP3 measurements.
The statistical analyses were performed using SPSS (version15; SPSS Inc. Chicago, IL, USA) and Info Stat version 2011 (Group Info Stat, FCA, National University of Cordoba, Argentina).
| Results|| |
The 172 adolescents accepted as participants were classified according to their audiometric profile in both frequency ranges as follows:
Group 1: 112 adolescents (with normal HTL).
Group 2: 21 adolescents (with a slight shift of HTL).
Group 3: 39 adolescents (with a significant shift of HTL).
The difference between the ears of the audiometric and TEOAEs profiles was not significant (P > 0.05). Thus, both ears were processed together for the statistical procedures.
[Figure 1] shows the mean HTL (audiometric profile) of adolescents with normal HTL (Group 1) and adolescents with slight and significant shift of HTL (Groups 2, and 3, respectively).
|Figure 1: Comparison of the audiometric profi les corresponding to the three groups of adolescents|
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The results showed significant differences between the audiometric profiles of:
- Group 1 (normal HTL) and Group 2 (slight shift of HTL), (P < 0.01) in all the frequencies assessed;
- Group 2 (slight shift of HTL) and Group 3 (significant shift of HTL), (P < 0.05) in the extended high frequency range from 10000 to 16000 Hz;
- Group 1 (normal HTL) and Group 3 (significant shift of HTL), (P < 0.01) in all the frequencies assessed.
The analyses of the TEOAEs amplitude showed low-level or absence in 16% of the ears. [Figure 2] shows the mean amplitude response of the ears with present and low-level or absent TEOAEs.
|Figure 2: Comparison of the amplitudes between ears with present and low-level or absent transient evoked otoacoustic emissions|
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The results showed significant differences (P < 0.01) between the amplitude of the ears with present and low-level or absent TEOAEs in all the frequencies assessed. A progressive decline was observed from the frequency 1500 Hz. The global amplitude showed statistical difference (P < 0.01) between the ears with present (mean amplitude 13.15 dB SPL) and low-level or absent (mean amplitude 4.13 dB SPL) TEOAEs. The same significant difference (P < 0.01) was found for reproducibility, with the mean of the ears with present (90.15%) and low-level or absent (65.82%) TEOAEs.
The audiometric profiles corresponding to the ears with present and low-level or absent TEOAEs were obtained, as shown in [Figure 3].
|Figure 3: Comparison between the two hearing threshold level corresponding to the ears with present and low-level or absent transient evoked otoacoustic emissions|
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The HTL corresponding to the ears with low-level or absent TEOEAs showed an increase in all the frequencies. A statistical difference (P < 0.05) was found in most frequencies with exception of (3000, 4000, 8000, 9000, and 12,500) Hz.
The amplitude of TEOAEs corresponding to the audiometric groups is shown in [Figure 4].
|Figure 4: Comparison of the amplitude of transient evoked otoacoustic emissions according to the audiometric groups|
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A general decrease was observed in the amplitude of TEOAEs in all the frequencies in accordance with the three audiometric groups, as well as a progressive decline from the frequency 1500 Hz in the three audiometric groups.
A statistical difference (P < 0.05) was found in the mean global amplitude, the reproducibility, and in the amplitude of the frequency 3000 Hz between Group 1 (normal HTL) and Group 2 (slight shift of HTL). Between Group 2 (slight shift of HTL) and Group 3 (significant shift of HTL) no statistic difference (P > 0.05) was found in the frequencies amplitude, in the mean global amplitude, and in the reproducibility. Between Group 1 (normal HTL) and Group 3 (significant shift of HTL) a statistical difference (P < 0.05) was found in the reproducibility, in the mean global amplitude, and in all the frequencies of both groups. The values of the mean global amplitude (dB SPL) and the reproducibility (%) of the three audiometric groups are shown in [Table 1].
|Table 1: Mean global amplitude and mean reproducibility of the three audiometric groups|
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Relationship between hearing and music exposure
The levels of participation in the musical recreational activities are shown in [Table 2] according to the audiometric groups.
|Table 2: Percentage of participation in each musical recreational activity by audiometric group|
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[Table 2] shows the participants' rate of participation in each recreational activity associated with loud music. The activities with the most participation are NA, and UPMP, with participation level concentrated between medium and high in all audiometric groups.
As shown in [Table 3] the distribution in frequency and percentage of the MGE by audiometric group.
|Table 3: Distribution of the musical general exposure by audiometric group|
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The association between the audiometric groups and the MGE did not show a significant statistical association (χ² = 2,633, P > 0.05). It must be taking into account that the frequency in one of the cells was smaller than five, so, this result should be considered cautiously. However, in Group 2 (slight shift of HTL and Group 3 (significant shift of HTL) the category High was the higher percentage of MGE (52.4% and 46.2% respectively).
A comparison between the categories of MGE and the audiometric profiles of the 112 adolescents of Group 1 (normal HTL) was carried out. Three audiometric profiles were obtained within this group, according to the adolescents' MGE [Figure 5].
|Figure 5: Comparison of the three audiometric profi les obtained from the group of adolescents with normal hearing threshold level by musical general exposure categories|
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The results show significant differences (P < 0.05), especially between the audiometric profiles of the groups with low exposure and high exposure to music in the most of the frequencies assessed, except in (250, 2000, 8000, 9000, and 11,200) Hz. There is a tendency toward a higher mean HTL in the group with high music exposure.
Taking into account all audiometric groups, statistical differences (P < 0.05) in HTL were also observed between the categories low and high of MGE in the frequencies (500, 1000, 2000, 3000, 6000, 9,000, 10,000, and 16,000) Hz.
The amplitude of the TEOAEs of all ears was also compared with MGE categories. The results showed no significant differences (P > 0.05) in the amplitudes by frequency, global amplitude, and reproducibility among the categories of MGE. Nevertheless, the amplitudes corresponding to high exposure tend to be lower than those of moderate and low exposure.
From the acoustic measurements carried out over 4 h in the four nightclubs the adolescents manifested visiting the most, the equivalent sound levels (LAeq) for each nightclub was obtained. These values are shown in [Table 4].
|Table 4: Equivalent sound levels from the measurements at the four nightclubs|
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The values of the manikin free-field equivalent sound level (LMFFAeq) obtained from the 10 MP3s measured are shown in [Table 5].
|Table 5: Manikin free-fi eld equivalent sound level from the measurements of 10 MP3s|
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| Discussion and conclusion|| |
A growing tendency has been observed for adolescents to expose themselves to nonoccupational noise during leisure activities, particularly those associated with loud music. ,,, Accordingly, current research considers exposure to loud music a social and public health risk that requires the development and implementation of strategies to prevent risky behaviors and promote auditory health. ,,
Considering this international tendency, as well as our previous studies on the topic, we designed a program which we have implemented in technical high schools to assess adolescents: Once at the age of 14-15 (test) and again at 17-18 (retest).  The overall goal of the program is to detect auditory disorders early on and analyze the development of auditory function when exposed to high music levels during adolescence when recreational habits are established and before exposure to work noise that may affect hearing. Here, we discuss the preliminary results obtained in adolescents from the first school evaluated.
Audiological assessment included standard audiometry as well as an EHFA and OAEs test. Both EHFA and OAEs are recommended for early diagnosis of NIHL. Frequencies higher than 8000 Hz may be more sensitive to noise than lower frequencies, thus hearing loss in these frequencies may predict NIHL in lower and speech specific frequencies.  OAEs may be particularly useful for NIHL detection since OHCs are known to be the elements of auditory processing that are the most vulnerable to noise overexposure. 
The results of our study showed significant differences in mean HTL among the three audiometric groups into which participants were classified. These differences were especially evident in the extended high range. Groups 2 (slight shift of HTL) and 3 (significant shift of HTL) compared to Group 1 (normal HTL), revealed an increase in HTL in all frequencies. In Group 3 (significant shift of HTL), the mean HTL was progressively rising toward extended frequencies, particularly from 10000 Hz on. Differences were also found in the conventional range, especially between Groups 1 (normal HTL) and 3 (significant shift of HTL), although to a lesser degree than in the extended range. These results are consistent with the idea that high frequency ranges are more sensitive to noise, ,,,, as found in our previous studies. , Furthermore, it has been suggested that EHFA may be useful for early diagnoses of auditory sensitivity to noise, thus preventing hearing loss in frequencies, especially involved in speech.
Previous studies carried out by the National Health and Nutrition Examination Surveys between the years 1988 and 1994 with 2519 adolescents aged 12-19 years, reported prevalence of NIHL (audiometric notches) of 15.9% in the conventional frequency range. In a new study between the years 2005 and 2006, about 14 years later, with 1791 adolescents of the same age group, the prevalence of audiometric notches increased to 16.8%, although this increase was not statistically significant. ,,
Nevertheless, in the Ohrkan study, recently carried out in 27 public and private schools in Germany, with the participation of 1843 students aged 15-16 years, hearing loss was seldom observed and the prevalence of audiometric notches in high and low frequency hearing level of the conventional range was minor. These results could not confirm the high prevalence of audiometric notches reported by former studies in the conventional range.  However, Twardella et al.  expressed that even if the empirical evidence is at present ambiguous, it is highly plausible that leisure noise can damage hearing. Thus, information and education about this potential risk among young people is warranted.
The TEOAEs analyses, we conducted to determine cochlear function, revealed absent and low level TEOAEs in 16% of the ears. In these cases, reproducibility, global amplitude, and amplitude by frequency decreased significantly compared to cases where TEOAEs were present. In both groups, TEOAE levels peaked at 1500 Hz followed by a progressive downward slope. These results are consistent with previous studies. , OAEs may be sensitive to subtle inner ear changes before NIHL occurs. ,, Low level and absent OAEs may be useful as predictors of NIHL. 
We found a relationship between HTL and TEOAEs, which was statistically significant in most frequencies. High HTLs were found in all frequencies in ears with absent and low levels TEOAEs, while the lowest amplitude was in Groups 2 (slight shift of HTL) and 3 (significant shift of HTL) with the greatest statistical difference between Groups 1 (normal HTL) and 3 (significant shift of HTL). Reproducibility and global amplitude decreased while HTL increased. Previous studies have shown that low OAE and reproducibility levels, together with normal HTLs, can indicate preclinical damage to the inner ear. ,,, Konopka et al.,  carried out a longitudinal study on the hearing effects of exposure to impulse noise, and the results showed that high frequency hearing loss can be associated with lower-frequency TEOAE changes.
Instead of TEOAEs, some authors  have analyzed DPOAE levels to answer the question of whether there are any measurable changes in hearing, especially in OHC operability, in subjects exposed to 3 h of loud music in a nightclub, and whether the two measures - DPOAEs and pure-tone thresholds applied before and after exposure - are similarly affected. They found that both pure-tone thresholds in the conventional frequency range and DPOAE levels were significantly deteriorated after 3 h of exposure to music at an average of 102 dBA in a nightclub.
The participation of the adolescents of our study in five recreational musical activities - EMH, PMI, LCA, NA, and PMP use - is consistent with the adolescent tendency to expose oneself to high sound levels in their free time. This exposure to loud music during recreational activities leads to an increased chance of negative effects on hearing. The results here obtained are consistent with other studies on the topic. ,, On the other hand, Petrescu  points out that attending live concerts and nightclubs and PMP use are the sources of nonoccupational noise that put one most at risk of developing some kind of hearing problem. Our study showed that these activities are also the most popular.
In our study, the comparison among the "participation levels" for each musical activity and the audiometric groups showed a similar distribution; and the three categories of MGE were not significantly associated with the audiometric groups, although in Group 2 (slight shift of HTL) and 3 (significant shift of HTL) the category high was the one with the highest participation rates. These results would suggest that leisure noise exposure along the time may potentially affect hearing.
The comparison of the HTL obtained for each category of MGE showed significant differences in the HTLs of some frequencies of both ranges between low and high exposure. In the particular analyses of Group 1 (normal HTL), significant differences were found in most of the frequencies between low and high exposure with a tendency to a higher mean HTL in the extended high frequencies from 11200 Hz in the group with high exposure. With further exposure to loud music during leisure time, as is expected in older adolescents,  the impairment found at this stage of our research, though small in some cases, is very likely to increase with age. Thus, the high exposure group may be at risk of developing some kind of hearing problem since hearing damage is accumulative and not considered dangerous at this age. However, the slide in HTL that occurs in early ages can cause a considerable reduction in hearing in old age. 
The difference in reproducibility, global amplitude, and amplitude by frequency among MGE categories obtained in our study was not significant. Nevertheless, the amplitudes by frequency corresponding to high exposure showed a greater decrease than moderate and low exposure. Similar results were found in a study where 30 disc jockeys were assessed before and after music exposure in nightclubs, revealing a significant decrease in amplitude for TEOAEs, DPOAEs, and temporary pure-tone threshold shift.  Other studies support these findings of a decrease in OAE amplitudes and temporary or permanent changes in pure-tone thresholds. ,,,
This study provides evidence that both methods, pure-tone threshold in the extended high frequency range - for early prediction of NIHL in the conventional range - and TEOAEs - as predictors of individual cochlear vulnerability to noise overexposure - should be applied in adolescents and young people to preserve and promote auditory health.
An important issue to take into account regarding NIHL is the different vulnerability to noise overexposure among the subjects, as some of them proved to have "tender" ears, which are more vulnerable to noise than "tough" ears, which tolerate a more extensive noise impact without harm. The underlying mechanism for this phenomenon is not completely understood. Some studies suggest that the efferent medial olivocochlear provides protection from noise overexposure and hence may be responsible for this characteristic. ,,
When it comes to recreational noise exposure, which frequently exceeds sound pressure level limits established for occupational noise exposure, there are hardly any regulations. One of the most common sources is amplified music at nightclubs or UPMPs at loud intensity levels. Sound pressure levels at nightclubs can easily exceed 100 dBA, which is thought to constitute a substantial risk for hearing damage. ,
Depending on the duration and intensity of noise exposure, either TTS or permanent hearing threshold shifts (PTSs) may occur. In the second case, it may occur at medium to high exposure levels when exposure time is long enough, however, PTS frequently occur slowly over time by accumulating gradual, irreversible damage to the sensitive OHC of the inner ear. Hence, regular high level noise exposure, such as that found in nightclubs, is expected to be harmful to hearing in the long run. Thus, an important issue in establishing hearing conservation programs is, besides education and prevention, the early detection of NIHL. 
In our study, the average sound levels (LAeq) measured at four nightclubs was 110.2 dBA (ranging from 107.8 to 112.2 dBA), similar to values obtained in previous measurements,  and a little higher than those published in other studies: Smith et al. 101.0 dBA; Goggin et al., 97.0 dBA; Williams et al., 97.9 dBA, as mentioned by Williams et al.  Furthermore, those who visit nightclubs stay there for on average of about 4 h/week. Hence, adolescent exposure to music sound levels equivalent to over 100 dBA at nightclubs exceeds, in all cases, the international recommendations for hearing conservation in occupational environments. The work place regulation considers a LAeq of 85 dB as borderline between "safe" and "dangerous" for 8 h of daily exposure, so that a LAeq of 100 dB during only 15 min would be equivalent to the total daily sound immission, considering an exchange rate of 3 dB by doubling or halving the time of exposure. 
At present, there are no regulations on leisure activities. A simple solution would be to simply apply the workplace noise exposure level to recreational activities, and use this as the maximum level that the society will accept as producing minimum harm in recreational places. 
On the other hand, the average manikin free field equivalent sound level (LMFFAeq) obtained from the 10 MP3 measured in our study was 95.8 (varying between 82.9 and 104.6 of LMFFAeq). According to the National Institute on Deafness and other Communication Disorders (NIDCD, 2007), NIHL results from exposure to sounds that are above 85 dBA, with sufficient periods of exposure time. Therefore, the values obtained in this study all, except one; exceed the recommended limit of sound exposure.
Similar results have been found by other researches. Levey et al.  measured free-field equivalent sound levels from PMP headphones of 189 college students, averaging 22.2 years of age, and found that 58.2% exceeded recommended sound exposure limits, placing them at risk for NIHL. Laboratory studies have found that PMP users sound intensity levels ranged from 79 to 125 dBA.  Another study that combined laboratory and real-world field study in public environments found that the average listening level of 60 participants was 82 dBA, ranging from 61 to 104 dBA. 
The European Commission's SCENIHR concluded that, considering the daily time spent listening to music through PMP and the typical volume control settings, approximately 5-10% of listeners are at high risk of developing permanent hearing loss after 5 or more years of exposure. The committee defined restrictive criteria for the use of PMPs, in which 1 h/day at a noise >89 dBA is considered a potential health risk. 
In spite of caution that should be exercised in generalizing the present findings because of the nonrepresentativeness of the sample - a reduced number of only male participants - the results obtained are important to keep in mind during the retest as well as during future studies.
Strategies preventing NIHL through programs that promote protective behaviors in adolescents, such as limiting daily listening time, controlling the UPMPs in noisy surroundings (e.g., public places or public transportation), and listening at moderate levels (60% of the music player's maximum volume), may be needed. Such strategies would be aimed at adolescents who can still receive the direct benefits of this activity, but through healthier habits.
The results obtained up to now indicate that, in some cases, beginning auditory decay is already evident, particularly in HTLs of extended high frequency range and in reproducibility, global amplitude, and amplitude by frequency of TEOAEs, at a young age of 14-15.
Since exposure to loud music begins at an early age and researchers have demonstrated the positive effects of educational programs in schools, ,, health promoting actions should be implemented in school-age children to increase their awareness of the risks of loud music.  Thus, children can achieve a better understanding of healthy listening habits and learn about ways to protect their hearing before their risky listening behaviors become habits, and at the same time, to establish hearing conservation programs for the early detection of NIHL.
| Acknowledgments|| |
The authors are grateful to the National Agency for Scientific and Technologic Promotion, the National Technical University, the Education Ministry of Cordoba, National Scientific and Technical Research Council (Argentina), the school were the study was carried out, and the adolescents participating in it.
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Dr. Mario R Serra
National Technological University, Cordoba Regional Faculty, Argentina, Maestro. M. Lopez esq. Cruz Roja Argentina, 5016 Cordoba
Source of Support: National Agency for Scientifi c and Technologic Promotion, National Technical University and National Scientific and Technical Research Council, Argentina,, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]