Objective: Noise measurement and frequency analysis of commercially available noisy toys were the main purposes of the study.
Materials and Methods: 181 noisy toys commonly found in toy stores in different zones of Tehran were selected and categorized into 10 groups. Noise measurement were done at 2, 25, and 50 cm from toys in dBA. The noisiest toy of each group was frequency analyzed in octave bands.
Results: The highest and the lowest intensity levels belonged to the gun (mean=112 dBA and range of 100-127 dBA) and to the rattle-box (mean=84 dBA and range of 74-95 dBA), respectively. Noise intensity levels significantly decreased with increasing distance except for two toys. Noise frequency analysis indicated energy in effective hearing frequencies. Most of the toys energies were in the middle and high frequency region.
Conclusion: As intensity level of the toys is considerable, mostly more than 90 dBA, and also their energy exist in the middle and high frequency region, toys should be considered as a cause of the hearing impairment.

Background and Aim: N-acetylcysteine, a glutathione precursor and reactive oxygen species scavenger, is reported to be effective in reducing noise-induced hearing loss. Many workers in industry are exposed simultaneously to noise and chemical pollutants such as carbon monoxide. We investigated effectiveness of N-acetylcysteine in protecting the cochlea from simultaneous noise and carbon monoxide damages.
Methods: Twelve rabbits were exposed simeltaneously to 100 dB sound pressure level of broad band noise and carbon monoxide 8 hours a day for 5 days. One hour before exposure, experimental group received 325 mg/kg of N-acetylcysteine while normal saline was administered for the control group. The protective effect of N-acetylcysteine was evaluated 3 weeks after exposure by histological assessment of the hair cells.
Results: Simultaneous exposure to noise and carbon monoxide resulted in a considerable damage to the outer hair cells however, the inner hair cells and the pillar cells remained intact. Use of N-acetylcysteine in the experimental group significantly reduced the extent of outer hair cell loss.
Conclusion: N-acetylcysteine attenuates simultaneous noise and carbon monoxide induced hair cell damage in rabbits.
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Background and Aim: Sound conditioning is exposure to a non-traumatic, moderate level of sound which increases inner ear resistance against further severe noise. In this study, we aimed to survey the effect of sound conditioning on auditory brainstem response (ABR) threshold shifts using click stimulus, and the effect of the frequency of conditioning on hearing protection.
Methods: Fifteen guinea pigs were randomly divided into 3 groups. Two conditioned groups were exposed to 1 kHz, and 4 kHz octave band noise at 85 dB SPL, 6 hours per day for 5 days, respectively. On the sixth day, the animals were exposed to 4 kHz octave band noise at 105 dB SPL, for 4 hours. The control group was exposed to intense noise, 4 kHz at 105 Db SPL for 4 hours (without conditioning). After exposure, ABR thresholds using click were recorded an hour, and 7 days after noise exposure.
Results: The results of the ABR with click stimulus showed less thresold shifts in conditioned groups than control (p≤0.001). Comparison of the results of conditioned groups, showed less threshold shift by 4 kHz conditioning, however, this difference was not statistically significant (p>0.05).
Conclusion: Electrophysiological data of our study showed that sound conditioning has a protective effect against subsequent intensive noise exposure, and the frequency of conditioning does not have significant effect on ABR threshold shifts when using click stimulus.