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Otoacoustic emissions in young adults exposed to drums noise of a college band.

INTRODUCTION

Recent research has shown that non-occupational noise exposure can cause damage to the auditory system.

Several studies relate and demonstrate the importance of the use of otoacoustic emissions (OAE) for the prevention and diagnosis of hearing loss in individuals exposed to noise, as they may present cochlear dysfunction despite a normal audiogram (1).

The OAE are sounds that are generated spontaneously or not in the hair cells of the inner ear , travel to the middle ear into the ear canal where they can be measured by a microphone. Therefore, the middle ear must be intact so that the sounds coming from the cochlea may be captured in ear canal (2-4).

The DPOAE arise from the non-linear integration of two simultaneous pure tones presented to the cochlea. The two tones have two different frequencies (f1 e f2), which are denominated primary frequencies. The best results are found in the frequency equivalent to 2 f1 f2, in the relation f2/f1 of 1,22 (5, 6).

The DPOAE may be obtained in different ways 7-9: DP Gram which shows the range of the emissions in several frequencies in a previously determined sound level; DP Growth Rate also known as DPOAE I/O (input/output) in which the responses are analyzed in a particular frequency in decreasing sound levels in order to find the threshold of the response to the presented stimulus and provide information on cochlear non- linearity.

Research concerning OAE, show the non-linearity of the cochlea, essential for a normal hearing function, cochlear compression and functioning of the external hair cells (8, 10-12). OAE are recommended to evaluate individuals exposed to noise in order to identify as early as possible alterations and/or to assess the progression of an already acquired hearing loss 113. The reduction of the DPOAE after exposure to noise is described in the literature (14), especially in the 5 and 6 kHz. Many studies show the possible use of the DPOAE I/O as an indirect measure of human cochlear nonlinearity (15,16). The slope of the function can be evaluated and a threshold can be determined, as an additional procedure to check hearing function 511'17. Threshold is defined as the lowest stimulus level producing a DPOAE that is 3 dB above the noise floor 9.

The growth rate may be measured in three different ways: area, slope or threshold. The area is the difference between response and noise floor. This measure provides the cochlear amplification mechanism (9). The slope inclination shows the cochlear nonlinearity: the slope decreases with the rise of the sound level. This reduction rate corresponds to the compression region of the growth rate and goes up to 80 dBSPL. The compression can be estimated as the difference between the low level threshold and high level maximum inclination (15). The more acute the cochlear lesions, the less inclined the slope (18, 19).

In teenagers with or without tinnitus, the high frequency audiometry and the TEOAE (up to 4.000 Hz) and DPOAE (up to 12.000 Hz) did not show statistically significant difference in the cochlear responses, thus suggesting that the external hair cells of teenagers with tinnitus might not be sufficiently damage to cause hearing impairment. The noise exposure time may be an important factor, since adults with tinnitus show hearing impairment. The use of personal stereos and noise exposure reduce otoaocustic emissions, despite there are being statistical difference (20).

Given that OAEs may show a trace of alteration even in subjects with normal thresholds if the audiogram is within the normal standards,

The importance of researching the OAEs in noise exposed young adults is based on the possibility of early identification even before a noise induced hearing loss can be detected in an audiogram.

Thus, the goal of the present study was to identify cochlear dysfunction and tinnitus in young adults exposed to noise of the college drum band

METHODS

Observational and cross-sectional survey approved by the Research Ethics Committee of Universidade Federal de Sao Paulo (UNIFESP), under protocol 542.452. The study procedures were explained verbally to participants, and those who agreed to participate signed the free informed consent. This study was conducted in the clinic of audiology of UNIFESP.

The sample was composed of 50 college students divided into two groups. The study group consisted of 25 students who participated in the college drum band. A control group with 25 students who did not participate in the band was composed. The groups were matched by gender and age, tested by ANOVA. The two groups aged 18 to 30 years should present normal otoscopy and tympanometric curve type A21. Students with conductive hearing loss at the time of collection, previous exposure to occupational noises and history of metabolic or genetic diseases were excluded.

The musical instruments used in the band are drums, percussion, tambourine, repinique and ganza. During the rehearsals, a single exploratory noise measurement was carried out of the college band using the cellphone app Decibelimetro HQ positioned at the height of the participants' ears. Three measurements were made, composed of twelve samples each, made during one minute, every five seconds22. The average values of the sound pressure levels obtained in the three measurements were, respectively: 96.2; 94.2; and 98.8 dBA.

Anamnesis was conducted to obtain data relate to hearing complaints, individual's history in the band, general health data and use of personal stereos which also may interfere in the cochlear function.

Tests of Transient-evoked Otoacoustic Emissions (TEOAE) and of Distortion-product Otoacoustic Emissions (DPOAE) were performed with ILO UBS-V6. The equipment has a probe which was positioned in external acoustic meatus of the individual. In TEOAE, a probe was used to present the non-linear stimulus covering a frequency range from 500 Hz to 4 kHz (both ears alternately) with levels ranging from 75 to 85 dBSPL. Responses at frequency ranges of 1,000, 1,500, 2,000, 3,000 and 4,000 Hz were investigated. The criterion used for analysis of presence was a response in dBSPL (signal to noise ratio) greater than or equal to 3 dB NPS, in each frequency range tested, general reproducibility greater than 50% and probe stability greater than or equal to 70% (23).

DPOAEs was evoked in the f2(s) from 1000Hz to 6000Hz with L1 = 65 e L2= 55 dBSPL. The criterion used to indicate the presence of DPOAEs was a response in dBSPL at least 6 dB above the first standard deviation of the equivalent noise, at each f2 tested (23).

The growth rate was obtained in the frequencies of 2 k, 3 k, 4 k and 6 kHz, registering the emissions responses due to the reduction of the levels of sound pressure in each frequency. The threshold of the DPOAE was considered as the lowest sound pressure level with the signal to noise ratio greater than 3 dB24. The stimuli f2 (L2) were presented with the variation of 20 to 65 dB SPL in steps of 5 dB, and the stimulus level f1 (L1) was carried based on the equation proposed by Kummer et al (1998), that is: L1= 0,4L2 + 39dB. The Slope was registered and compared between the groups so that one could measure the inclination of the of the responses of the growth rate.

A one-way ANOVA was performed in order to compare to compare age between the groups, otoacoustic emissions responses, thresholds and Slope. The Spearman Test was also used to verify correlations between the questionnaire variables and the OAEs responses. The p value less than 0.05 was considered significant.

RESULTS

The study group and the control group had more women, 88%, because they attended a course, Audiology and Speech Therapy, mostly attended by women. The average age of the control group was 20.5 years and of the study one was 20.6 years, with no difference between the groups (p= 0.849--ANOVA). Most of the subjects (76% control and 60% study) did not suffer from otitis. Those who did had it in childhood (75%).Most did not present tinnitus (80% CG e 64% EG). When there was tinnitus, in most (92.3%) it was sporadic and high-pitched. Of the assessed individuals, 78% used personal stereos, of which 60.5% for a period of up to 30 minutes a day, 31.6% from 30 to 60 minutes and 7.9%, for 60 minutes or more.

The average time of participation in the drums band was one year and 92 days. Regarding the rehearsal, in average, they rehearsed for a day and half per week, lasting an hour and a half. Most of the participants did not use an earplug (Table 1).

Spearman's correlation analysis was done to verify correlations between the data of the questionnaires. There was a positive correlation between the incidence of tinnitus (frequency and form) and the variable time in the drum band and rehearsal days and hours. Thus, the greater the number of days, time and hours of rehearsal in the drums band, the more frequent the tinnitus. There was also correlation between the use of personal stereos and tinnitus, as the more these devices were used, the greater the occurrence of tinnitus (Table 2).

In the comparison between the groups, there was smaller general response to TEOAE in the study group in both ears (Table 3), with a significant difference between the groups (ANOVA). There was no statistically significant difference between the groups when compared by frequency bands.

Regarding the DPOAE in the frequency of 6,000 Hz in both ears, there was a tendency of the control group to present better response (Table 4).

There was no statistically significant difference between the groups in relation to the average values of the slope of the DPOAE I/O, from 2,000 to 6,000 Hz in the right and left ears. There was only a tendency (p value: 0,085) of a smaller value of the slope in the study group in 2 kHz in the right ear.

The average threshold of the growth rates of distortion from 2,000Hz to 6,000Hz varied from 38 to 42.8 dBSPL with no difference between the groups (p value greater than 0.05).

DISCUSSION

The most willing and assiduous individuals were those who had been with the drum band for over two years, which may have been a determining factor for the results of the present research. Most individuals did not rehearse for very long with the band: 60% rehearsed only one day a week and the majority did it for only an hour (72%). The greater the rehearsal, in hours, the greater the tendency to present tinnitus. The musicians of the present study with longest time with the band, more days and hours of rehearsal presented greater occurrence of tinnitus. Tinnitus was reported in 23.5% in the study group and in 27.7% in the control group, with no statistically significant difference. However, there was a positive correlation of the variable tinnitus with the time in drum band and the rehearsal hours. Workers exposed to noise have predominantly bilateral tinnitus of the "wheezing" kind", more frequently during the night and correlated with the level of noise. The longer the exposure and the higher the level of sound pressure, the greater the occurrence of tinnitus (25, 26). Such results are consistent with the present study, as the musicians who had been longer in the band, and rehearsed for more days and hours presented tinnitus more frequently.

The use of personal stereos, a habit that may be considered a risk to hearing, was found in 78%. Research shows that the excessive use of these devices is growing due to urbanization and the advance of technology and it may cause hearing alteration due to the time and loudness of the music and it may even diminish otoacoustic emissions (20, 22, 27, 28).

Regarding the use of hearing protector, 80% of the individuals did not use any king of protection despite the sample being composed of Audiology and Speech Therapy students. Thus, awareness campaigns and protection measures should be intensified in the community.

The average levels of sound pressure during the rehearsals were higher than 96 dB(A) which could be harmful to hearing. Despite the fact that noise assessment was not the goal of the present investigation, it is worth highlighting that even those who were exposed to high levels, rehearsed for only an hour, in average. Therefore, if we consider the Regulatory Norm 15 of the Brazilian Ministry of Labor and Employment, the daily acceptable level of noise exposure is of 1 hour and 45 minutes (29). Thus, considering the age of the subjects and the little time of the exposure, we believe that the results obtained in the present study were within the expected.

The permanent change of the hearing threshold may occur due to the continued exposure to loud sounds mainly if there is no rest between the exposure. Noise-induced Hearing Loss (NIHL) is influenced by factors such as: physical characteristics of the noise (type, level of sound pressure and spectrum), exposure time (frequency and hours) and individual susceptibility (26, 30). In the present study, to avoid that even short exposures to high sound levels could influence the results of the testes, procedures were only carried out at least 48 hours since the last rehearsal of the drum bands. Furthermore, we also used as inclusion criterion the presence of type A tympanometric curve to ensure there were no alterations in the middle ear at the time of the exam which might have influenced the results. Thus, the OAE identification was more reliable.

The exposure to noise in industrial workers and or musicians may cause the reduction of the transient and distortion products otoacoustic emissions. In fact, studies have demonstrated that when there are alterations in a third of the external hair cells, the tonal audiometry remains normal with reduction in the OAE which we found in our study. Research has revealed that the greater the exposure to noise, the smaller the response found in the tests, mainly in 4 and 6KHz (f2) in both ears131. In the present study, there was a similar result with the reduction of the TEOAE in the group exposed to noise. Furthermore, in the DPOAE, there was a reduction of response in 4 k and 6 kHz (f2) in the study group, in the right ear and a tendency to smaller response of DPOAE in 6 kHz(f2). This result was expected, as the literature shows higher incidence of hearing alteration first in the higher frequencies as they are more susceptible, especially in the region between 3 and 6 KHz, in individuals exposed to noise (1, 29, 32,33).

The average threshold of the growth rate in the DPOAE varied from 38 to 41,8 dB, like those found in the literature (5, 34, 35). There was not a statistically significant difference between the two groups. In DPOAEs I/O, the responses were obtained from 30 to 75 dBSPL, being the greatest response in the frequency of 6 kHz (f2) of the right ear, with 75 dBSPL, in the study group. The smallest value was obtained with 30 dBSPL, in both groups. In the literature, a study obtained the best response in 1000 and 2000 Hz, and 45 dBSPL for 4000 and 5000 Hz and 70 dBSPL as the highest threshold for all the frequencies under test (5), similarly to the one reached in our study.

The slope reflects the cochlear non-linearity which decreases with the rise of sound pressure of the stimulus and with cochlear lesion. After the exposure to the noise, the slope may seem more inclined and with smaller values and it may indicate an alteration in the compression mechanism of the external hair cells. In other words, there is a steeper growth rate in cochlear disorders (36). This pattern was not observed in the present study as the slope values ranged from 0.4 to 1.0 dB, with no difference between the groups. There was only a tendency to smaller values in the study group in the frequency of 2,000 Hz in the right ear. Such result was also observed in another study which analyzed the growth rate of the emissions in normal-hearing adults with and without tinnitus, identifying higher thresholds in 2,000 Hz in the group with tinnitus, characterizing the 2,000Hz frequency as the most vulnerable (16). The Slope values obtained in the present study are similar to the ones found in the literature concerning normal-hearing adults whose average values are close to 1dB (12, 37, 38).

In view of these results, the participants were informed about the importance of the use of earplugs and the deleterious effects of noise to hearing, as well as the importance of audiology monitoring in order to prevent future hearing loss.

CONCLUSIONS

Young people exposed to noise presented a lower amplitude of otoacoustic emissions evoked by transient stimulus, when compared to non-exposed ones.

The occurrence of tinnitus correlated with the time of exposure and use of personal stereo, thus, the longer the exposure to noise, the greater the occurrence of tinnitus.

doi: 10.1590/1982-0216201719512216

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(38.) Buzo BC. Emissoes otoacusticas produto de distorcao: estudo da funcao de crescimento em individuos com limiares audiometricos normais. [dissertacao] Sao Paulo (SP): Pontificia Universidade Catolica de Sao Paulo; 2007.

Paula Botelho da Silva (1)

Ana Claudia Fiorini (1)

Marisa Frasson de Azevedo (1)

(1) Universidade Federal de Sao Paulo UNIFESP/EPM --Sao Paulo/SP--Brazil.

Conflict of interest: Nonexistent

Received on: February 08, 2017

Accepted on: August 10, 2017

Mailing address:

Paula Botelho da Silva

Rua Coronel Carlos Ambrogi, 235 Pirituba, Sao Paulo, Sao Paulo, Brasil

CEP: 02969-130

E-mail: paulabot.silva@hotmail.com
Table 1. Distribution of time on the college drum band, days and hours
of rehearsal and the use of hearing protector in the study group (n =
20)

Variable                     n        %    Average    Standard
                                                      Deviation
             1-12 months     9        36
Time on      12-24 months    9        36   1.92       0.812
the band     25 or more      7        28
             1               15       60
Rehearsal    2               8        32   1.56       0.870
 days        4               2        8
Rehearsal    1               18       72   1.28       0.458
hours        2               7        28
Hearing      yes             5        20   1.80       0.408
Protector    No              20       80

Table 2. Distribution of the correlation data among the variables
of the questionnaire

Variable                           Otitis   Tinnitus   Personal
                                                       Stereos

Tinnitus             [r.sub.s]     -0.16    .997       .126
Frequency            P             913      .000**     .388
Personal             [r.sub.s]     .157     .116        --
Stereos              P             .275     .422        --
Time with the        [r.sub.s]     -.289    .344       .179
band                 P             .162     .092       .191
Rehearsal            [r.sub.s]     .052     .0140      .315
days                 P             .804     .505       .126
Hours                [r.sub.s]     .052     .282       .067
                                   .804     .172       .751

                     Time on the   Days     Hours      Hearing
                     band                              Protector
Variable
                     .358          .175     .338       .627
                     0.79 *        .403     .098 *     .001 **
Tinnitus             .179          .315     .067       .047
Frequency            .191          .126     .751       .824
Personal                           .345     .512       .079
Stereos                            .091 *   .009 *     .726
Time with the        .345          --       .463       -.152
band                 .091 *        --       .020        .468
Rehearsal            .512          .463      --         .089
days                 .009*         .020      --         .672
Hours

Statistical method: correlation test of Spearman

Table 3. Distribution of general responses of TEOAE

VariableGroups    Mean    SD      Mini   Maxi   F       P
                                  mum    mum            value

TEOAE   Study     20.41   5.26    12.3   31.4   12.37   .001 *
Right   Control   28.34   9.96    12.3   45.7
Ear
TEOAE   Study     21.00   5.62    10.3   35.2   5.48    .023 *
Left    Control   30.05   18.48   12.3   102
Ear

Statistical Method: ANOVA test
TEOAE: Transient evoked otoacoustic emissions
SD: Standard deviation
F: Frequency
P-value.: Significance

Table 4. Distribution of the DPOAE responses, per ear and group

DPOAE                Mean     Median   Standard    CV
SD (RE)
                                       Deviation
1 kHz    Study       12.6     12.2     4.5         35%
         Control     11.1     12.1     5.6         51%
2 kHz    Study       16.9     17.4     5.3         32%
         Control     18.5     18.5     6.3         34%
3 kHz    Study       15.2     15.7     6.0         39%
         Control     15.9     15.6     5.4         34%
4 kHz    Study       18.5     17.9     5.6         30%
         Control     19.2     19.9     4.4         23%
6 kHz    Study       15.8     15       6.8         43%
         Control     19.3     20.5     6.5         34%

DPOAE    Min         Max      n        IC          P-value
SD (RE)

1 kHz    3.9         23.4     25       1.7         0.301
         0           19       25       2.2
2 kHz    6.6         29.1     25       2.1         0.323
         3.2         28.2     25       2.5
3 kHz    3.7         26.1     25       2.4         0.655
         6.8         29.5     25       2.1
4 kHz    6.4         29.3     25       2.2         0.601
         7.3         28.2     25       1.7
6 kHz    4.3         29       25       2.6         0.070
         7           29.7     25       2.6

DPOAE    SD (LE)     Mean     Median   Standard    CV
                                       Deviation

1 kHz    Study       10.8     10.3     5.6         52%
         Control     10.8     11.9     7.3         67%
2 kHz    Study       16.6     17.6     6.1         37%
         Control     17.2     17.4     6.9         40%
3 kHz    Study       15.5     16.5     5.4         35%
         Control     14.4     13.5     6.6         45%
4 kHz    Study       18.3     19       6.1         33%
         Control     18.1     17.6     6.4         35%
6 kHz    Study       15.9     15.4     5.8         37%
         Control     18.9     21.3     6.0         32%

DPOAE    Min         Max      N        IC          P-value

1 kHz    0           23.2     25       2.2         0.988
         0           23.6     25       2.9
2 kHz    4.3         29.4     25       2.4         0.757
         4.3         30.6     25       2.7
3 kHz    6.2         28.3     25       2.1         0.526
         5.2         28.6     25       2.6
4 kHz    8.3         31.3     25       2.4         0.923
         6.5         32.9     25       2.5
6 kHz    6           28.8     25       2.3         0.081
         8           29.9     25       2.4

Statistical Method: ANOVA test

DPOAE: Distortion Product Otoacoustic Emissions

SD: Standard Deviation

F: Frequency

P-value: significance
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Title Annotation:Original articles. Texto en ingles
Author:da Silva, Paula Botelho; Fiorini, Ana Claudia; de Azevedo, Marisa Frasson
Publication:Revista CEFAC: Atualizacao Cientifica em Fonoaudiologia e Educacao
Date:Sep 1, 2017
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