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Ever come out of a concert with ringing in your ears wondering if you’ve permanently damaged your hearing? It’s easy to just take your hearing for granted, but a lot of what you do while you’re young can have a big impact on the future health of your ears. How loud is too loud?Generally, experts agree that anything above 85 decibels is “too loud”, says audiologist Louise Dickinson from Acoustix Hearing. While the “85 dB” threshold gives a general guide, it also matters how long or often you’re exposed to the noise. Think you might have a problem?While more men than women suffer from hearing loss, with one in ten New Zealanders experiencing hearing related issues it’s essential to get your ears checked out if they’re of concern to you. What does an audiologist do?When you go to an audiologist, they’ll usually recommend a hearing test which costs about $80. The next time you’re at a club or concert, don’t stand too close to the DJ console or speakers. When listening to loud music at home, position your speakers so they project away from the direct path of your ears. For those who love DIY projects, pop into a hearing clinic to get custom-molded hearing protectors to reduce excessive noise levels to a safe level. If you work in a pub or club, get custom-molded hearing protectors that reduce loud music and other excessive noise (like the sound of empty bottles breaking) to a safe level.
Occupational hearing loss has long been recognized as a result of workers' exposure to loud noise. This donation benefits charities that we work with who are focused on helping Marines and their families.
All deployed Marines are equipped with Ballistic Hearing Protection (BHP), a two-sided, dual-purpose earplug that protects against steady-state noise and impact noise produced from aircraft, vehicles, machinery, gunfire and explosions. It is protective to 190 decibels (dB), which is greater than the noise of a jet fighter during take-off, with afterburners at a distance of 50 feet (130 dB). The efficacy of N-acetylcysteine to protect the human cochlea from subclinical hearing loss caused by impulse noise: A controlled trial.
It has been estimated that 16% of late-onset hearing loss in adults worldwide (9% in Western Europe) is due to occupational noise. Noise protection with N-acetyl-l-cysteine (NAC) using a variety of noise exposures, NAC doses, and routes of administration.
Dose and time-dependent protection of the antioxidant N-L-acetylcysteine against impulse noise trauma. Pharmacological rescue of noise induced hearing loss using N-acetylcysteine and acetyl-L-carnitine.
The effectiveness of N-acetyl-L-cysteine (L-NAC) in the prevention of severe noise-induced hearing loss. Effectiveness of 4-hydroxy phenyl N-tert-butylnitrone (4-OHPBN) alone and in combination with other antioxidant drugs in the treatment of acute acoustic trauma in chinchilla.
Radical scavengers for Meniere's disease after failure of conventional therapy: A pilot study. Efficacy of the antioxidant N-acetylcysteine (NAC) in protecting ears exposed to loud music. Noise in magnetic resonance imaging: No risk for sensorineural function but increased amplitude variability of otoacoustic emissions.
Hearing expert Dr Anne Greville says “occasional exposure to loud noises is normally not damaging to hearing, but can be if you’re exposed regularly”. Anne recommends seeing an audiologist who is a Member of the NZ Audiological Society (MNZAS). If you are worried you have a hearing problem but also have symptoms of other medical problems, it’s best to see your GP first.
Some hearing clinics also perform free hearing screenings, which are a quick way to see if you have a hearing problem or not (see below for an exclusive offer for nzgirls from Acoustix Hearing). Your employer has a legal duty under the Health and Safety in Employment Act to provide hearing protection for employees exposed to noises above 85 decibels. While there is much that is understood about how excessive noise causes hearing loss, there are many other aspects that are not understood. When the yellow side of the earplug is inserted into the ear, the BHP will block loud impulse noise without suppressing critical ambient sounds such as verbal commands. Effects from shooting on hearing thresholds were small, but threshold behavior supports use of NAC treatment.
In general, if you’re exposed to noises above 85dB regularly or for more than 8 hours continuously, you need to get some hearing protection. Impact noises like hammering and impulse noises like gunfire are too fast-acting for the ear to protect itself against and are worse than steady noises. These screenings involve testing your ears at 4 frequencies (500, 1000, 2000 and 4000 Hz) and if a problem shows up, a full hearing test is recommended.
It is now recognized that many different factors can cause occupational hearing loss: noise, pharmaceuticals, aging, genes and ototoxic chemicals.
When turned around, so that the green end is inserted into the ear, it provides steady protection against constant, high-level sound sources. Exposure to noise causes metabolic oxidative stress and the production of reactive oxygen species (ROS) resulting in cochlear injury.
If you’re on a really tight budget, visit your local Hearing Association for a cheaper hearing test. Those effects were like those from continuous noise, which means that strict safety measures should be enforced. These reduce background noise interference with the music and significantly lower the volume desired for listening. The most striking finding was that the non-linearity of the cochlea, that was strongly reduced in the group without NAC, as manifested by the PMTF-results, was practically unchanged in the NAC-group throughout the study. The method that is most promising for human use is to deactivate free radicals with antioxidants. Vitamins A, C, and E are free radical scavengers, and the combination is highly effective to reduce both hearing loss and cochlear cell death. In some studies an adjuvant (magnesium or salicylate) was reported to be needed to elicit the protective effect of antioxidants.

NAC has been tested in animal models, and has been shown to provide hearing protection in several studies. However, in military services the noise levels are often extreme, and in some situations there can be doubts if level-dependent ear-muffs provide enough attenuation for all subjects.
The noise levels are enhanced and the noise character is changed by reflections of the sound by the concrete walls. Urban warfare training has been considered to be a health problem with increased risk for NIHL by the Health Authorities of the SAF. This and other acoustic hazards have enforced the need for a treatment programme to be applied directly after an acoustic accident. Antioxidants offer such an opportunity.The purpose of the investigation was to study how an antioxidant, NAC, can prevent discrete cochlear physiological functions being affected if the drug is administered directly after extreme noise exposure in military personnel. Two of the officers were women.The NAC group consisted of 11 officers of whom six participated in both parts of the experiment.
Five of those who participated in both experiments had apparent effects of the noise exposure in the first experiment, one of the six showed only minor effects. 4 years.The audiograms before shooting, measured according to the next paragraph, are shown in [Figure 1]. These conditions were exactly the same for both groups.In the control condition sound pressure levels were registered by a reference microphone placed on a stand about 2 m from the weapon in the bunker, in the companion's left ear canal and in the shooter's right ear canal by three miniature microphones. The variation in these levels did not show any significant relation to the results in the hearing tests. Four tablets were taken, all of them after exposure: The first tablet, dissolved in half a glass of water, was taken directly after exposure, a second tablet 1 h later, a third one at breakfast the next day, and the fourth and last one an hour later. The duration is 275 ms, including attack- and release times, and with a 175 ms long interval between pulses. The level of the tone decreases with the same speed until the button is released again, etc. The threshold is calculated as the mean value of the medians of the remaining upper and lower turning points with a resolution of 1 dB. These parameters should give a high threshold resolution with a standard deviation of repeated measures not exceeding 1.8 dB. An ear with a lesion has a decreased capacity to detect for example soft sounds after loud sounds.The threshold of a brief tone, 4 ms, is measured in a 100% sinusoidally intensity-modulated octave-band noise. Separate thresholds are measured with the tone at the peaks and in the valleys of the noise.
To prevent listening to sounds outside the octave-band, a faint, periodic, broadband masking noise is added.
The measurements were performed at 4000 Hz, with a modulation frequency of 10 Hz and at the noise levels 25 to 95 dB SPL, in steps of 10 dB. The left ear of each subject was tested, since this ear is more sensitive to noise than the right one. The standard deviation for repeated measurements is about 2 dB for peak and valley thresholds.
Further details about the method can be found in Lindblad et al.[19] Experiments with quinine, which causes a transitory hearing loss, have shown that PMTF is a sensitive test of the function of the outer hair cells (unpublished data). Thus PMTF-measurements have proved valuable for testing high quality hearing, as required for example from sonar operators. A sensorineural hearing loss decreases the height of the maxima and moves them toward higher sound pressure levels. The values at the local maxima of the peak- and valley-threshold curves have been used in statistical analyses and so have the respective noise levels (x-values) of these maxima.In our research about susceptibility to noise induced hearing loss we have found that results from conscripts with basically continuous noise exposure are similar to results from people with sensori­neural hearing loss. Those who have been subjected to shooting incidents with unprotected ears - with impulse noise of not too extreme levels - develop in a contrary way. An example of an accidental impulse noise exposure is shown in [Figure 3], which shows the test results of a conscript at the beginning of military service and and after the accident. The maxima, both on the peak-threshold-curve and the valley-threshold-curve, move toward 45 dB SPL - and they become extremely high.
A contralateral noise was applied to test the function also of the efferent system controlling the outer hair cells.
The measurement was performed in a non-linear mode to enhance those components in the response, which have a non-linear dependence of the stimulus level, and to suppress the linear components. To accomplish this the polarity of every fourth click is reversed and the sound pressure level is increased by a factor of 3. The acoustical responses from 1000 clicks are averaged, after removal of the primary click by windowing-technique.
The RMS-value for the broadband response (the response that is correlated to the clicks), over the interval of measurement, is used as a variable in the analyses as well as the RMS-values in 1000 Hz-bands. Also the uncorrelated response is analysed in 1000 Hz-bands.In another of our projects the same type of effects as for the PMTF-results appeared for the TEOAEs. For the control group hearing tests were scheduled and performed in a house about 100 m from the bunker on the day preceeding the shooting training and on the day of shooting. When we tested the first subjects we found that PMTF-results were affected at the measurement about 4 hours after shooting. As a result PMTF-measurements were added on the next day for them, and for some subjects also about a week later. For the NAC group test occasions on the next day and 1 week later were scheduled from the start. Therefore further follow-up measurements could not be made.A test setup with three measuring systems allowed for hearing tests to be performed on three people at a time. The test parameters for each type of test were chosen to make it possible to start new measurements every 15 minutes [Table 1]. The hearing tests directly after the shooting were performed at the same time for both subjects in a pair. There was no time to evaluate if possible changes in otoacoustic emissions after the measurements had come to an end on the shooting days. For all subjects in the NAC group all the types of measurements were performed again during the next day.If, for a person in the control group, the inspection of results in 7) so implied, further measurements were performed about a week after shooting.
Statistical analysis The program Statistica 9.1 with the module "General linear models" was used for statistical analyses.

Although six subjects participated in both groups they were treated as different subjects in the statistical analyses. This could give less strength to the analyses but decreased risk of Type I errors.Ethical approvementThe investigations were commissioned by the SAFs. This analysis was performed for the measurements from before shooting until, and including, 3 hours after shooting, the last measurement of the control group.
However, in [Figure 4], the NAC group shows a tendency to recovery between 3 hours after the shooting and the next day. Since all the subjects in the NAC group were measured on the next day and next week a separate ANOVA was performed for this group only, with the hearing thresholds at the three frequencies 3, 4, and 6 kHz as dependent response variables and with frequency, ear, and time as repeated factors. Circles = right ear, crosses = left earClick here to viewDuring the measurements we noticed that after shooting the subjects took longer time for each threshold and there were unusally large intraindividual variations over time.
As an indicator of these fluctuations, both toward worse and better thresholds, we therefore calculated the standard deviation (and variance) for each subject and frequency over the six measurements from the test occasion before shooting up to 3 hours after the shooting.The intraindividual standard deviations in the present study showed the same general frequency dependence as standard deviations for repeated thresholds at conventional audiometry using the same headphone [Figure 5]a.
Data for the headphone were taken from an unpublished study of standard deviations for various headphones by one of the authors.
The left ear looked only slightly more influenced by the noise exposure than the right ear. An ANOVA calculated with the individual variances of the hearing thresholds as the dependent response variable, and with frequency, and ear as repeated factors within subjects and group as a factor between subjects showed no significant effect of NAC (P=0.38). Therefore a simple t-test of the intraindividual standard deviations for the left ears in the two groups (both groups exposed to noise but with or without NAC) was made and showed an almost significant effect, P=0.06 (one-sided test, unequal variance). Psychoacoustical modulation transfer function The generally most worth-while way of analysing the PMTF-results is to use the thresholds at the maxima of the peak- and valley-curves. In this study the maximum peak- and valley-thresholds show interesting results.A look at the individual results in the control group revealed that for most subjects the maxima were decreasing between the day before the shooting and three hours after exposure, with further decrease in maxima until the next day for several subjects. Clear decreases of the maximum peak thresholds are seen from the test occasion before shooting, to the result at the end of the shooting day, 3 hours after shooting. NAC) as a factor between subjects and with peak-valley and time (before, 3 hours after, next day) as repeated factors within subjects.
It can also be noted that in the control condition, on the next day, both peak and valley thresholds were even more affected but the difference from 3 hours after shooting was not significant. Each symbol indicates the same subject in both parts of the figureClick here to viewFigure 7: PMTF-results.
Mean of left ear maximum peak thresholds (left) and mean of left ear maximum valley thresholds (right) over time for the control group (N = 23, dashed lines), and the NAC group (N = 11, solid lines).
A Tukey's post hoc test showed that the correlated response in the NAC group was significantly higher 3 hours after the shooting than before. There were a few other interactions that were significant, but without interest for the question of the protective effect of NAC. Among these the factor group was significant (P response type was significant, with the mean level of the correlated response 3.9 dB above that of the uncorrelated response for these relatively normal hearing test subjects.
However, they have failed to demonstrate a large beneficial effect of NAC in reducing temporary threshold shifts. There were no significant differences in temporary, noise-induced pure tone shift (TTS), or shift in DPOAE amplitude in the two groups. In the NAC group there was an increase in correlated TEOAE response 3 hours after shooting. However, the main differences observed between the groups existed already before shooting and might be attributed to age difference. The control group included a few older officers with larger total exposure, and therefore worse thresholds, but less frequent shooting exercises lately and higher OAE products.The most striking discovery was that the non-linearity of the cochlea, expressed by the PMTF-findings, was practically unchanged in the NAC-group throughout the study.
In the control group there was a highly significant decrease in non-linearity after the noise exposure and it was still decreasing at least until the next day for several subjects.Effects of NAC treatment were found for all the three types of hearing measurements. The hearing thresholds showed no conventional TTS after noise exposure, with or without NAC. However, we observed an increased threshold variablitity of the left, noise sensitive, ear in the control group after noise exposure, but not in the NAC-group. However, in the present study the hearing thresholds were measured repeatedly, and TEOAEs were measured only once 3 hours after exposure.
The variability of thresholds in our study supports Wagner's interpretation, since NAC reduced the threshold variability in the left ear.
We can only speculate, like those authors, that there were individual varieties of metabolic and structural processes going on in the inner ear causing the large intraindividual variation in thresholds. The results are contradictory with reports of no MOC influence, [34],[37] and with signs of such an effect when the MOC function was measured after the exposure.
In another project (not yet published) we found hyperactivity after shooting, which might be interpreted as reduced ipsilateral control of OHC. One interpretation is that also NAC, at some stage, reduces the ipsilateral control of the OHC.The PMTF group results, but not every subject's results, changed towards the direction of a sensorineural hearing loss caused by continuous noise exposure both with and without NAC [Figure 2]. Without NAC treatment the results continued to deteriorate at least until the measurement the day after exposure. Similar to the hearing thresholds, the reference values of the PMTF (taken the day before exposure) also differed between the groups. For future planning it may be kept in mind that for those in the control group, that had an extra PMTF-measurement 20-30 min after exposure, there was no difference from the results before exposure.
The characteristics of the test results, but not the time course of the recovery, indicated exposure from continuous noise-after this exposure to impulse noise in reverberation. The results of the experiment with NAC, in a clinical, low dosage, indicates some protection of the cochlea. This is promising considering the small effects on hearing from the ethically defensible noise exposure, the small and unmatched test groups, and the NAC medication taken only after exposure.
Administration of NAC gave some significant changes of the physiology of hearing after exposure.

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