Habits and hearing complaints of teenagers users of personal stereos

Results: all participants of the study get exposed to music, the most them less than two daily hours. It was observed the presence of the suppression effect in the right ear in 66,67% and in the left ear in 61,90% of teenagers. Was not found significant association among the presence of the suppression effect between the ears, the genders, times daily noise exposure and absence of suppression effect. The sample of the teenagers reported having tinnitus, these, most reported tinnitus in both ears. Had significant association between the daily noise exposure and the presence of tinnitus and between the absence of the suppression effect of right ear and the presence of tinnitus.


INTRODUCTION
Equipments such as portable stereo devices are popular among young people ant they are frequently used for many hours during the day, with high sound pressure levels 1,2 .This abusive use with high duration, intensity and/or frequency of exposure to music may lead to auditory function disorders [3][4][5][6] and it may cause severe consequences to life quality 7 .
The occurrence of auditory symptoms such as hypoacusis, ear fullness or dizziness and tinnitus after using personal stereos may suggest higher risks to young people's hearing 5,6,8 .It indicates a relationship among these symptoms and the habit of using personal stereos 5 .
However, youths do not seem to be worried about the harmful effects of intense sounds.It becomes clear when it is considered their attitudes in varied situations of sound exposure 9,10 , thus, it is important to perform researches about teenagers personal stereo users 11,12 .
A symptom which is associated with improper sound exposure is tinnitus 3 .It is considered a perception by individuals of sounds or noise with no external sound source 8 and it may occur after neuroplastic alterations in the peripheral auditory pathways and, mainly, central, which may appear through peripheral injuries 13 .
Nevertheless, there are few studies related to tinnitus in this age group, because children and teenagers usually do not refer such complaint.It is important to highlight that tinnitus may cause concentration, sleep and learning interference, becoming an important symptom to be investigated, because it is common in this population 3 .According to a recent study, as longer is the time of headsets use, higher is the tinnitus occurrence 6 .Besides, another study observed that people with tinnitus may present alteration of medial olivocochlear tract function, observed through lower otoacoustic emissions suppression 14 .
Through the suppression effect, it is evidenced normal operation of the medial olivocochlear (MOC) system, after otoacoustic emissions amplitude reduction, when applied noise against or ipsilaterally the examined ear.Such phenomenon occurs because of the medial olivocochlear tract fibers, in synapse with exterior ciliated cells, occurring, thus, reduction of basilar membrane movement 15 .
Thus, researching the MOC system operation in teenagers may be effective to obtain the relationship between hearing and auditory habits and exposure type of these subjects.Besides, the lack of emissions in these young individuals may express cochlear impairments, which can be detected even before this impairment becomes clinically evident 11 .
Taking into account that teenagers are part of a group which is exposed to high levels of sound intensity, habits which are considered as risky to auditory health, and also observing that there are not many studies about this age group, this study had the purpose of characterizing auditory habits and complaints of normal hearing teenagers, users of personal stereos, and relating them with the medial olivocochlear system activity.

METHODS
This is a prospective, quantitative, descriptive and comparative study, with the purpose of investigating a possible association between auditory habits and complaints of teenagers, users of personal stereos, and the absence of suppression effect.The participants were selected from municipal schools in Cerro Branco, RS, Brazil.After information about procedures, al parents signed the Informed Consent, according to the standard 196/96 by the National Commission for Ethics in Research (CONEP/1996).In this term there were procedures, risks and benefits, responsibility commitment about eventual damage, identity confidentiality assurance, as well as research declaration of consent and participation.
The selected study subjects were teenagers from 7th and 8th municipal school grades who agreed in participating in this research, with the following inclusion criteria: cognitive skills to respond the evaluations, audibility thresholds compatible with normal hearing, meatoscopy with no alterations, absence of middle ear and TEOAEs present in both ears.All subject who did not present the inclusion criteria were not part of the study.
It was performed visual inspection of the external acoustic meatus, hearing screening and impedance test.For external acoustic meatus visual inspection, it was used an otoscope Heine mini 3000®.The hearing screening was performed through auditory thresholds research airway in frequencies from 250Hz to 8 kHz with audiometer by Interecoustics, model AD229E in silent environment.To perform the immitance measures, it was used the middle ear analyzer INTERACOUSTIC AZ7, with phone TDH-39 and MX-41 cushion, with probe tone from 220Hz to 70dBNA and ISO standard calibration 389-1991.As normal hearers were considered the subjects with thresholds up to 25 dB, classified according to the World Health Organization 16 , and type A tympanogram in both ears 17 .The teenagers who presented any type or degree of hearing alteration were excluded from the research and submitted to complementary treatments.
The number of screened teenagers was 23, from three municipal schools from Cerro Branco who accepted to participate in the research.From them, two subjects were excluded from the research because of audiological alteration.The study final sample consisted of 21 teenagers, all right-handed.
All subjects were submitted to the TEOAEs register and analysis test with the equipment OtoRead, by Interacoustics.The used pass/fail criteria were the ones described in the equipment protocol: click stimulus; 83 dBNPS intensity; number of tested frequency ranges: six (from 1500Hz to 4000Hz).The "pass" result was considered when the emissions presented signal/noise relation of 4 dB in at least three frequency ranges.
Then, it was researched the suppression effect, using noise contralateral stimulation generated by the audiometer, through headsets, intensity of 60 dBNA.The TEOAEs supression calculation was performed through the subtraction of the TEOAEs response level without contralateral acoustic stimulation from the TEOAEs response with contralateral acoustic stimulation.Positive values indicated presence of TEOAEs suppression and negative values or zero indicated suppression absence.The suppression effect analysis was performed in Response, which was calculated through geometric average of all frequency ranges tested by ear, in each individual.It was considered the presence of TEOAEs suppression effect when the responses averages with and without contralateral stimulation was greater than or equal to 1 dBNPS 18 .
It was performed the application of a closed questionnaire, regarding auditory behavior and complaints about tinnitus.After the questionnaire responses, it was observed the following variables: number of daily hours of music exposure, presence of tinnitus and where there was tinnitus.After responding the questionnaire and performing the auditory evaluations, it was raised study hypotheses and, then, it was performed statistical analysis.
The data was tabulated and statistically analyzed.For all the variables, the frequency tables were calculated.To analyze the association between the presence of suppression effect between genders and ears, and the association between the presence of tinnitus and the presence of suppression effect, it was used the Chi-Squared Test.For the association between time of daily sound exposure and presence of suppression effect and the association between presence of tinnitus and time of daily sound exposure, it was used the non-parametric Mann-Whitney U Test (for both independent samples).The considered significance level was 5%, indicating significant difference among the evaluated variables.

RESULTS
The studied teenagers are between 12 and 19 years old.Most of them are 13 years old (23.80%), followed by 12 years (19.04%) and 14 years old (19.04%).All 21 subjects (100%) referred they listen to music, 47.62% (n=10) referred music exposure for less than two hours a day, 19.05% (n=4) of them referred music exposure from two to three hours a day and 33.33% (n-7) of them referred music exposure from three to four hours a day.
About the presence of suppression effect, in the right ear 66.67% (n=14) of the subjects presented suppression effect and 33.33% (n=7) did not present the effect.In the left ear, 61.90% (n=13) of the teenagers presented suppression effect and 38.10% (n=8) did not present such effect.
In the comparison between the ears, it was not found difference between the presence of suppression effect in the right and left ear.It proves that the ears are independent (p=0.075).
In relation to gender, 57.14% (n=12) of the researched subjects are female and 42.86% (n=9) are male.When it was performed the analysis of suppression effect presence in relation to male and female subjects, it was not found difference between the groups, as for the right ear (p=1.00) as for the left ear (p=0.19).About the right ear, as for male, as for female, 66.67% (n=14) of the subjects presented suppression effect.In relation to the left ear, 53.85% (n=7) of the male teenagers presented suppression effect and 46.15% (n=6) of the female teenagers presented suppression effect.
There was no association between time of daily exposure and absence of suppression effect in both ears (Table 1).exposure and presence of tinnitus, it is observed that the longer is the time of music exposure, the greater is the presence of tinnitus (Table 2).
The association between suppression effect and complaint of tinnitus occurred only in the right ear (Table 3).
In relation to the presence of tinnitus, 33.33% (n=7) of the teenagers reported presence of tinnitus.From them, 28.57% (n-14) reported tinnitus in both ears and only 4.76% (n=1) reported tinnitus in the right ear.There was not any report of tinnitus only in the left ear.

DISCUSSION
Teenagers, according to recent studies, have demonstrated harmful habits and behavior considered as improper to hearing health 19 .Such habits are explained in relation to adolescence concepts and usual association with high music 20 .
In another study 10 , a larger part of the researched teenagers did not demonstrated concerns about the possibility of hearing loss caused by the use of personal stereos.Among these subjects, a considerable number reported hearing personal stereo for three or more hours a day.The authors observed that this is probably tem uma regulamentação para exposição sonora em atividades de lazer, pode-se levar em conta dados do Ministério do Trabalho, que estabeleceu uma Norma Regulamentadora nº 15 (NR 15) que determina limites de tolerância de 85 a 115 dB (A).A partir da primeira intensidade, verifica-se que a cada aumento de 5 dB (A) o tempo máximo diário de exposição deve ser reduzido à metade 28 .
the group with the greatest risk to acquire hearing loss 10 .The present research found similar data, as some teenagers referred music exposure for three to four hours a day.
A recent study observed that a considerable number of teenagers referred exposure to high levels of sound pressure, using personal stereos for a longer period 6 .
In the present study it was researched the decrease in the levels of TEOAEs responses magnitude in the presence of contralateral acoustic stimulation.It shows that the contralateral noise produced TEOAEs suppression effect, which is related to the action of the efferent auditory system, according to the data by other authors 21 .It was evidenced in the present study, in most teenagers, as in the right as in the left ear.This results are similar to other studies 22,23 which also found suppression effect in a considerable part of the sample, which consisted of normal hearing individuals.
The absence of OAEs suppression effect, evidenced by the increase of the OAEs amplitude, suggests medial olivocochlear system alteration 23.This dysfunction may occur in the presence of partially injured outer hair cells, when the inner hair cells are working well, without altering the audiometric thresholds 24 .Such absence occurred in the researched individuals, evidencing the importance of researching teenagers' hearing, even when they do not refer auditory symptoms or complaints, because there are risks factors in this age group and there are other facts related to this absence of suppression factor.For instance, there is disorder on school performance 25 , considering the importance of medial olivocochlear system integrity for learning.

Table 1 .
Relationship between daily noise exposure and absence of suppression effect in both ears *Statistically significant values (p≤0.05)-Mann-Whitney's U Test Legend: RE = right ear; LE = left ear; N = number of subjects; % = percentage in relation to the number of subjects.

Table 2 .
Occurrence of tinnitus in relation to daily sound exposure *Statistically significant values (p≤0.05)-Mann-Whitney's U Test Legend: N = number of subjects; % = percentage in relation to the number of subjects.

Table 3 .
Occurrence of Suppression Effect in both ears in relation to presence of tinnitus