Introduction: Several animal studies have been performed that demonstrates a relationship between the amount of magnesium ion in the plasma and the hearing thresholds following exposure to noise, Mg++ has been considered as an effective factor in  prevention of noise induced hearing loss in animals.The aim of this study was to discover whether Mg for a long period of time have a protective effect on occurrence of Noise Induce Hearing loss.
Method: The subjects were randomly chosen among individuals who were under training in army service for two months. The subjects were treated in a double-blind manner by placebo and magnesium ion. Threshold estimation and blood examination was performed for all subjects before and after treatment. All subjects were exposed to noise during 8 weeks training in the army.
Results: The statistical difference between two groups which was treated with placebo and magnesium ion was significant.
Discussion: This study is compatible with previous in vivo observations and animal studies demonstrating the protective effects of magnesium on noise-induced impairment of inner ear.

Introduction: We estimated the noise in an industrial shoe factory to determine the effect of noise in the workplace on the hearing status of the workers in such environments.
Materials and method: the intensity of noise in dB in different parts of the factory was estimated. Then working people in each part was selected randomly and their hearing thresholds were evaluated by Conventional audiometry.
Results: The results demonstrated that 23% were required to estimate thresholds more precisely and 95 needed close examination by Otolaryngologist. Besides, 10% of the workers suffered sensory neural hearing loss whose 2% of them diagnosed as NIHL.
Discussion: Since the mentioned factory has good hearing conservation program for the workers, it seems that promoting the program can decline the number of noise induced hearing losses to the least numbers.

Background: Many Endogenic and exogenic factors can affect the individual&aposs susceptibility to noise exposure, for instance middle and outer ear characteristics, the amount of oxygen transmission, skin color, medical history, mental state and the patient&aposs attention, age, cigarette smoking and many otjher factors affect the amount of noise induced hearing loss and acoustic trauma.The current study was aimed at investigate the impact of various Endogenic and exogenic factors on the amount of PTS and TTS in veterans in Hamedan province.
Results: The results of the study manifested that:- Veterans with tinnitus suffered more hearing loss than patients without this symptom.- Extended intensity of noise and exposure time to war noises can exacerbate the amount of hearing loss in veterans who had fight more.- The degree of hearing loss in patients who had previously suffered middle ear infections or otitis or the familial history of hearing loss was more than people without such history
Discussion: The findings of our study in compatible with the results of other similar studies and confirms the effect of different pathologic and non-pathologic factors on the degree of noise induced hearing loss.

Tinnitus from the Latin word tinnire meaning ringing is the perception of sound within the human ear in the absence of corresponding external sound. The most common cause is noise induced hearing loss. Tinnitus may be induced by an acoustic trauma or a permanent noise in the workplace. In case that Tinnitus is induced by acoustic trauma the site of lesion is commonly the base of the cochlea. Tinnitus in the senile population is mostly accompanying presbycusis. Although the incidence of permanent tinnitus following noise exposure is high, little is published about this issue. In the current article we are aimed at studying the prevalence of tinnitus in Minoo and other manufactures.

There are increasing evidences about the vestibular damage caused by the exposure to noise. Histological and functional derangements of the vestibular system have been reported in laboratory animals exposed to high levels of noise. However, clinical series describe contradictory results with regard to vestibular disturbances in industrial workers and military personnel suffering from noise induced hearing loss (NIHL). Animal studies have proved that crista ampullaris bears the most disturbances, though some damages have been also detected in macula of the utricle and saccule and utricle. These changes have been induced due to acoustical pressure on the vestibular labyrinth. The findings from the experiments regarding vestibular function in patients suffering NIHL have shown a paramount diminish in vestibulo-occular Reflex (VOR). The correlation among NIHL, VOR and unilateral caloric weakness were statistically significant which can be due to a common mechanism of disturbances in the function of cochlea and vestibule.

The most common contributing factors in inducing hearing loss in adults are aging, exposure to noise and the interaction among these factors with other parameters. Individual parameters are also effective in the extent of hearing loss which is produced. Being aware of Vulnerability factors such as physical parameters, Auditory and non-auditory factors can be useful in considering a good hearing conservation program for noise induced hearing losses.In the current article we are aimed at introducing three important parameters and their sub-divisions pertaining to this issue.

Method and Materials :this cross sectional descriptive and analytic survey was done at Golestan navy hospital in Tehran, between June 1998 and March 1999 on total of 69 male subject (104 ears, ) 50 acoustic trauma & 54 noise induced H.L) between 20 to 40 ears old.
Results:1- The mean acoustic reflex threshold at 1 kHz showed there is no significant difference between two groups.
2- The intensity elicited maximum reflex amplitude at 1 kHz didn&apost produce at a significant linear correlation with subject&aposs age and ear canal volume in both groups.
3- The intensity elicited maximum reflex amplitude in NIHL group wasn&apost shown a significant correlation with ear compliance and gradient.
4- The mean Intensity (SPL) elicited maximum reflex amplitude in NIHL group was more than mean intensity (SPL) in acoustic trauma group.
5- The mean intensity (SL) elicited maximum reflex amplitude in NIHL group was More than mean intensity (SL) in acoustic trauma group.
Conclusion: Acoustic reflex amplitude is reduced for subjects with NIHL compared with acoustic trauma subjects.

Background and Aim: Hearing sensitivity is so vital for musicians as loud music can cause hearing loss. The aim of this study was to assess hearing sensitivity of musicians in order to determine the effects of music exposure on hearing organ.
Materials and Methods: This case-control study  was conducted on 15 string musicians with musicianship history of more than 10 years and 15 normal hearing subjects. They all were male and 20-30 years old. TEOAEs and DPOAEs performed after otoscopy , immittance and pure tone audiometry in octave frequencies between 250 to 16000 Hz.
Results: There is not significant difference between pure tone thresholds of two groups for all frequencies.A significant difference of TEOAE is found between two groups for total response and amplituds of TEOAEs . DPOAEs amplituds are not significantly different between two groups .
Conclusion: Musicianship may  affect TEOAEs amplitudes , but cannot affect results of PTA and DPOAEs. Therefore this can be useful to detect cochlear lesions secondary to music exposure and also as a tool in hearing protection program.

Background and Aim: Balance disturbance is one of the non-auditory effects of noisy industrial environments that is usually neglected. The aim of the current study was to investigate the effect of occupational noise on vestibular system among workers with noise-induced hearing loss (NIHL), based on both vestibular evoked myogenic potentials (VEMP) and caloric tests.

Methods: Thirty male workers with noise-induced hearing loss and thirty male matched controls were examined by VEMP and caloric tests. Study parameters included unilateral weakness, p13 and n23 latencies, and p13-n23 amplitude. Caloric test was performed only for 20 patients.

Results: No significant difference was observed in unilateral weakness between the two groups. On the other hand, the difference in mean latencies of p13 in the right ear (p=0.003) and left ear (p=0.01) was significant between the two groups. However, the difference in n23 latency was significant only in the right ear (p=0.03). There was no significant difference between groups in p13-n23 amplitude.

Conclusion: It seems that pars inferior of vestibule is the susceptible part in individuals with NIHL. In general, abnormal findings in both VEMP and caloric tests were more common compared to functional symptoms such as vertigo, which may be due to central compensation and the symmetry of the disorder.

Background and Aim: As word recognition score test is one of the most important tests in audiologic test battery and there is no study on reliability and validity of existing monosyllabic word lists, we decided to investigate this in people with noise induced hearing loss.

Methods: In this non-randomized descriptive-analytic study, 30 adults with noise induced high frequency hearing loss with the age of 18 to 46 years were evaluated. Construct validity was evaluated by comparing Mosleh lists with list NU-6 and reliability was achieved by test-retest (-two-week interval).

Results: The mean (SD) score of word recognition was 94.01 (3.95) percent for list 2, 90.40 (4.90) percent for list 4, 89.08 (4.43) percent for list 5, and 94.10 (4.11) percent for list 9. A reliability of 94% was achieved in all four lists . Regression analysis revealed that word recognition score (WRS) had decreased in proportion to pure tone average.

Conclusion: Four lists have good construct validity. All word lists are phonetically reliable too.