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How to cite this article Barreto MASC, Costa CSA, Guarita LKS, Oliveira CACP, Bahmad F Jr. Introduction: Exposure to continuous or impulse noise may lead to High Sound Pressure Induced Hearing Loss (HSPIHL) or to acoustic trauma in soldiers. Among the several elements of occupational risk, exposure to noise is one of the agents which produces the most harmful effect on the auditory health of individuals exposed, as it may trigger hearing alterations with varying degrees, as well as non-auditory problems which will reflect on their social, family and workplace behavior1. Firearm explosion noise is one of the main causes of High Sound Pressure Induced Hearing Loss (HSPIHL) in the United States and an ever increasing number of people have been affected by acoustic trauma or gradual Sensorineural Hearing Loss (SNHL) secondary to excessive firearm noise2. Shooting and other activities related to a military career may be linked to exposure to high levels of noise, which may produce alterations in the auditory system.
Soldiers, unlike industry professionals do not have a definite cycle of exposure, and may be occupationally exposed both to firearm impulse noise as well as in the artillery or even to other kinds of noise. Technological progress has made it possible to assess the cochlear function objectively by means of an evaluation of the Evoked Otoacoustic Emissions (EOAE). The paucity of studies in South America about the hearing of soldiers exposed to impulse noise and considering the applicability and the preventive character in hearing monitoring by means of the EOAE test, stimulated the conduction of the present study, with the purpose of studying distortion product otoacoustic emissions (DPOAE) before and after the exposure to impulse noise and the presence of tinnitus in soldiers of the Brazilian Army. The application of the questionnaire and the test by means of the DPOAE was performed at the Battalion of the Presidential Guard, in Brasilia, at the Federal District. The study group was composed of 60 male soldiers, aged between 18 and 19 without previous exposure to occupational noise.
After shooting practice with 7.62mm caliber FAL Rifles, they were all allocated into two groups.
The DPOAEs were assessed through the simultaneous presentation of two different pure tones (f1 and f2), expressed by the ratio of 1.22. The proportion of normal results (present response) in each frequency range before the shooting practice (100%) was compared with the proportion of normal results at the same frequency range after the practice using a proportion z-test (Yates' correction).
Post hoc analyses showed that the average amplitudes of all the frequencies assessed are different from each other (2>4>3>6>8KHz; Figure 1).
No association was detected between the Group and Occurrence variables of responses in any of the frequencies assessed in the Right Ear (Figure 3). A significant association was found in the left ear (Figure 4) between the variables when analyzed at the frequency of 6KHz. As for the presence of tinnitus, Table 1 shows the distribution of the frequencies of the variable presence of tinnitus for each kind of result in each group.
One can observe in Chart 1 that nine out of the fourteen studies were clinical studies conducted with soldiers exposed to impact noise.
It was observed that between 2000 and 2010 there was a predominance of studies with soldiers from the Army involving exposure to impulse noise (Chart 1). The present study did not detect a significant difference when comparing the right and left ears. Once again, differences were observed between the right and left ears, which differs from the findings of the present study, in which we found no difference between the ears tested, probably because in the present study the soldiers made use of hearing protectors. As for the effectiveness of the use of hearing protection devices, in 2008 Bockstael et al. Such findings are consistent with those of the present study, since, although we have found differences at some frequencies, others were practically unaltered, which suggests that the hearing protection device used was relatively effective. In the present study, it was observed that the DPOAEs showed subtle changes after the exposure to impulse noise, there having been a slight recovery in the subjects evaluated 24 hours later in comparison with those reevaluated immediately. Several authors abroad have used the EOAETs to evaluate the differences before and after exposure to impulse noise. As for the hearing protection, it was observed that for soldiers although there are previous instruction procedures about the need for the use of the hearing protection devices during shooting activities, in practice, there is still no surveillance as to their effective use.
In the present study hearing protection devices were distributed to all soldiers who participated. Such data have demonstrated that it is necessary to implement a Hearing Loss Prevention Program (HLPP) for soldiers, as long as they are exposed both to impulse noise and to continuous noise in their working environment. Although tone audiometry is recommended as a procedure for auditory evaluation, the DPOAEs proved sensitive to changes occurring after exposure to impulse noise, it being possible to conduct the test in military facilities.

As for the prevention measures used in the present study, they proved partially effective, and the use of hearing protection devices which offers a higher level of attenuation of noise or even equipments with automatic frequency adjustment (active auditory protector) may be recommended.
As for the tinnitus, considering the findings of the present study, there was a significant association between the presence of tinnitus and the group evaluated. Auditory monitoring by means of evaluation of the cochleain soldiers of the Brazilian Army exposed to impulse noise.
Auditory evaluation by means of evoked otoacoustic emissions (EOAE) has been demonstrating its importance in the detection of subtle changes in cochlear function still unidentified in threshold tone audiometry in subjects exposed to noise. So, noise is a constant problem in the Armed Forces, as long as it is an inherent risk agent in the military service, firearm impulse noise being one of the most damaging to hearing. This is a quick, objective and non-invasive method which may detect early cochlear alterations, first and foremost in subjects exposed to noise, unidentified by tone audiometry5. Group 1 (G1) with 30 soldiers was reassessed immediately after exposure to the impulse noise whereas group 2 (G2), also composed of 30 individuals, was reassessed 24 hours after exposure. In order to capture the DPOAEs, use was made of the equipment Eclipse from Interacoustics, which automatically monitored the level of noise, the linearity of the stimulus during the test and the appropriate position of the probe.
Sphericity was not assumed and the Greenhouse-Geisser method was used for the correction of the degrees of freedom. The chi-square test (Fisher's exact test) was used to m test the possible association between the Group and the Occurrence of responses, and between altered results and the moment of evaluation after-practice (immediately afterwards or 24h later). This effect does not depend on the group assessed and on the time, being a characteristic feature of each frequency which could be observed due to the sufficiently large size of the sample. In G2, the percentage of occurrence of responses at the frequency of 6KHz was significantly smaller than in G1. There was no significant association between the presence of tinnitus and the results in either of the groups (Figure 5). All were conducted in Europe or in the United States, demonstrating that studies with soldiers exposed to impact noise in Brazil are still scarce and it is a fact that soldiers are exposed both to continuous noise and to impact noise during their activities. However, after analyzing them individually, it was observed that, as far as the amplitudes are concerned, the absolute values in the right ear were slightly higher than in the left ear, regardless of the frequency analyzed. Nevertheless, according to the studies described, the active hearing protection device or even the shell variety is more effective to prevent subtle changes in the otoacoustic emissions which may become permanent alterations after years of exposure to impulse noise. However, the studies which used the DPOAEs for that purpose are scarce in the literature, which justifies our difficulty in comparing the results obtained in the present study. However, as has been described, the hearing protector devices is partially efficient to protect completely the ears from the impulse noises. That would also prevent the onset of auditory symptoms such as hearing loss, tinnitus and a full ear feeling, as well as prevent non-auditory symptoms resulting from hearing loss, besides contributing to social and economic aspects resulting from the treatment after the onset of the pathology. It can be observed that 3 subjects in G1 complained of tinnitus although their tests were normal after exposure, which leads us to consider the complaint irrespective of the objective observation in the test and it is suggested that such subjects be reevaluated after another exposure to impulse noise in order to investigate if the early complaint indicates an objective alteration observed in the DPOAE test or not.
In the soldiers exposed to impulse noise these cochlear alterations were accompanied by the tinnitus symptom mainly in the individuals reevaluated immediately after exposure.
Au, Speech therapist at the Brasilia Area Military Hospital (HMAB), Speech therapy Graduate (UFSM-RS); Speech Therapy Postgraduate (UFSM-RS), Psychopedagogy.
Au, Speech therapist at the Brasilia Otorhinology Institute, Speech Therapy Graduate (UCG-GO), Specialist in Audiology (CEDIAU-SP).
M.D, Second-year Otorhinolaryngology Medical Resident at the Federal District Base Hospital (HBDF-DF), Medicine graduate from the State University of Ceara (UECE-CE). M.D, PhD, Chief of the Otolaryngolgy and Head and Neck Surgery Department of the Brasilia University Hospital, Chairman of the University of Brasilia Medical School. Objective: Studying Distortion product otoacoustic emissions (DPOAEs) before and after exposure to impulse noise in soldiers of the Brazilian Army. As the consequences of that exposure are manifold and reach large proportions, the contingent and the sums involved are high, besides affecting the administrative, judicial and financial spheres4. In conclusion, after the exposure, both groups showed a decrease of the response amplitude, but in the group assessed right afterwards the decrease was higher. We can conclude that the decrease in the response amplitude was not the same for each frequency.

The p-value refers to the association test (χ2, Fisher's exact test) between the variables group and occurrence within each frequency.
The p-value refers to the association test (?2, Fisher's exact test) between the variables Group and occurrence within each frequency. The authors conducted auditory evaluation by means of threshold tone audiometry, transient evoked otoacoustic emissions (TEOAE) and DPOAE in 285 soldiers before and three weeks after exposure to gun impulse noise and artillery and in 32 subjects in the control group. The otoacoustic emissions proved more sensitive to cochlear monitoring than to tone audiometry.
The authors evaluated the subjects before and between 2 and 10 minutes after the shooting practice and observed that the shell variety hearing protection devices were effective to prevent changes in the threshold in the threshold tone audiometry and that there were significant changes in the response amplitudes in the EOAETs. Therefore, it is suggested that active protectors with frequency selectivity be used which could make it possible to understand the commands and orientations during the activities performed, or even passive hearing protection devices such as those used by Bockstael in 200810. It can also be observed that after 24 hours, subjects practically did not have tinnitus complaints, which leads us to hypothesize that if the organism had not recovered the cochlear function completely, at least subjectively an improvement was felt to have taken place. A eficiencia das emissoes otoacusticas transientes e audiometria tonal na deteccao de mudancas temporarias nos limiares auditivos apos exposicao a niveis elevados de pressao sonora. Estudo comparativo das emissoes otoacusticas evocadas em militares expostos e nao expostos ao ruido.
Distortion product otoacoustic emissions before and after one year exposure to impulse noise. Evaluation of transient and distortion product otoacoustic emissions before and after shooting practice.
Effectiveness of hearing protector devices in impulse noise verified with transiently evoked and distortion product otoacoustic emissions. Hearing threshold shift measured by otoacoustic emissions after shooting noise exposure in soldiers using hearing protectors. Material and Method: This is an analytical, observational, longitudinal and prospective study. The authors evaluated 54 soldiers with ages ranging from 20 to 22 years for two days of shooting practice, having evaluated the DPOAEs 1h before and 5 minutes after shooting6. Changes in the threshold and significant changes in the EOAEs between 2 and 4kHz in the ears were identified in the group under study. So, the decrease in the levels of the EOAETs and DPOAE in soldiers exposed to noise may be an early indication of potential hearing loss and may play a role as a screening method for soldiers exposed to noise and as a tool for monitoring early cochlear alterations9.
The exams were compared before and immediately after the shooting practice, and 1 hour later.
They observed changes at 3KHz in the tone audiometry and in the EOAETs confirming the EOAET test as being more sensitive than tone audiometry in the evaluation of temporary changes in the cochlea caused by impulse noise11. Auditory evaluation was performed by means of DPOAEs in 60 soldiers before and after exposure to impulse noise, of whom 30 were reevaluated immediately after exposure and 30 were reevaluated 24 hours after exposure.
The increase in the sensitivity of the EOAEs in comparison with the audiometric thresholds was shown in all analyses and the low level of the EOAE may indicate an increase in the risk of future auditory loss7.
Subsequently, both kinds of EOAE were evaluated in 31 subjects before and after the exposure during a five-daylong military practice. Results: The statistical analysis revealed that both groups reevaluated after exposure to impulse noise showed a decrease in amplitudes in comparison with the tests before exposure. There were significant differences between the ears in most cases; the EOAEs of the right ear tended to be more robust.
There were no significant alterations in the EOAEs before and after exposure, or after several days in the second experiment, suggesting that the active hearing protectors were able to prevent cochlear damage10. This demonstrated the applicability of the DPOAE test in monitoring the hearing of soldiers exposed to impulse noise.

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