Tinnitus and other auditory problems - occupational noise exposure below risk limits may cause inner ear dysfunction.

The aim of the investigation was to study if dysfunctions associated to the cochlea or its regulatory system can be found, and possibly explain hearing problems in subjects with normal or near-normal audiograms. The design was a prospective study of subjects recruited from the general population. The included subjects were persons with auditory problems who had normal, or near-normal, pure tone hearing thresholds, who could be included in one of three subgroups: teachers, Education; people working with music, Music; and people with moderate or negligible noise exposure, Other. A fourth group included people with poorer pure tone hearing thresholds and a history of severe occupational noise, Industry. Ntotal = 193. The following hearing tests were used: - pure tone audiometry with Békésy technique, - transient evoked otoacoustic emissions and distortion product otoacoustic emissions, without and with contralateral noise; - psychoacoustical modulation transfer function, - forward masking, - speech recognition in noise, - tinnitus matching. A questionnaire about occupations, noise exposure, stress/anxiety, muscular problems, medication, and heredity, was addressed to the participants. Forward masking results were significantly worse for Education and Industry than for the other groups, possibly associated to the inner hair cell area. Forward masking results were significantly correlated to louder matched tinnitus. For many subjects speech recognition in noise, left ear, did not increase in a normal way when the listening level was increased. Subjects hypersensitive to loud sound had significantly better speech recognition in noise at the lower test level than subjects not hypersensitive. Self-reported stress/anxiety was similar for all groups. In conclusion, hearing dysfunctions were found in subjects with tinnitus and other auditory problems, combined with normal or near-normal pure tone thresholds. The teachers, mostly regarded as a group exposed to noise below risk levels, had dysfunctions almost identical to those of the more exposed Industry group.

The efficacy of N-acetylcysteine to protect the human cochlea from subclinical hearing loss caused by impulse noise: a controlled trial.

In military outdoor shooting training, with safety measures enforced, the risk of a permanent, noise-induced hearing loss is very small. But urban warfare training performed indoors, with reflections from walls, might increase the risk. A question is whether antioxidants can reduce the negative effects of noise on human hearing as it does on research animals. Hearing tests were performed on a control group of 23 military officers before and after a shooting session in a bunker-like room. The experiments were repeated on another group of 11 officers with peroral adminstration of N-acetyl-cysteine (NAC), directly after the shooting. The measurements performed were tone thresholds; transient-evoked otoacoustic emissions, with and without contralateral noise; and psycho-acoustical modulation transfer function (PMTF), thresholds for brief tones in modulated noise. Effects from shooting on hearing thresholds were small, but threshold behavior supports use of NAC treatment. On the PMTF, shooting without NAC gave strong effects. Those effects were like those from continuous noise, which means that strict safety measures should be enforced. 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. NAC treatment directly after shooting in a bunkerlike room seems to give some protection of the cochlea.

Noise-induced tinnitus: a comparison between four clinical groups without apparent hearing loss.

The number of people with normal hearing thresholds seeking medical help for tinnitus and other hearing problems is increasing. For diagnostic purposes, existence/nonexistence of lesions or combinations of lesions in the inner ear not reflected in the audiogram was evaluated with advanced hearing tests applied to tinnitus patients with certain backgrounds, including noise exposure. For forty-six patients with pronounced tinnitus, and other symptoms, tentative diagnoses were established, including judgments of the influence of four causative factors: (1) acoustic trauma, (2) music, (3) suspected hereditary, and (4) nonauditory, for example, stress or muscular tension. They were analyzed with a test battery sensitive to lesions involving the outer hair cells, damage from impulse noise, and dysfunction of the efferent system. There were significant differences in test results between groups with individuals with the same most likely causative factor. Most patients claiming acoustic trauma had a specific type of result, 'hyper-PMTF' (psychoacoustical modulation transfer function), and abnormal test results of the efferent system. Everyone in the hereditary group had dysfunction of the efferent system. All patients working with music, except one, had some abnormality, but without specific pattern. The nonauditory group mostly had normal test results. The investigation shows that it is possible to diagnose minor cochlear lesions as well as dysfunction of the efferent system, which might be causing the tinnitus. Those abnormalities could not be detected with routine audiological tests. Malfunctioning caused by impulse noise is an obvious example of this. These findings facilitate choice of treatment, rehabilitation programs, and medicolegal decisions.

Successful and unsuccessful users of bilateral amplification: differences and similarities in binaural performance.

Bilateral amplification seems to be the best solution for bilaterally hearing-impaired persons. Nevertheless, some individuals are unsuccessful with this strategy. The goals of the present study were to develop tests to improve the diagnostic test battery before rehabilitation of hearing-impaired persons with bilateral or unilateral amplification, and to evaluate the tests with normally-hearing subjects and with two groups of hearing-impaired persons. The latter two groups contained 11 successful and 11 unsuccessful users of bilateral amplification respectively. Hearing thresholds, speech recognition in noise, signal analysis ability, binaural abilities, and dichotic tests were used in the investigation. The subjects answered a questionnaire and hearing aid gain curves were measured. The results for the two groups were similar for peripheral hearing functions and binaural performance. The unilateral amplification group showed significantly worse results in speech-in-noise and dichotic tests. Spatial aspects within the questionnaire were correlated to amplification preference. We therefore suggest the inclusion of speech-in-noise, dichotic tests, and questions on spatial orientation into the diagnostic scheme before rehabilitation with hearing aids.

Audiological findings in workers exposed to styrene alone or in concert with noise.

Audiological testing, interviews and exposure measurements were used to collect data on the health effects of styrene exposures in 313 workers from fiberglass and metal-product manufacturing plants and a mail terminal. The audiological test battery included pure-tone audiometry, distortion product otoacoustic emissions (DPOAE), psychoacoustic modulation transfer function, interrupted speech, speech recognition in noise and cortical response audiometry (CRA). Workers exposed to noise and styrene had significantly poorer pure-tone thresholds in the high-frequency range (3 to 8 kHz) than the controls, noise-exposed workers and those listed in a Swedish age-specific database. Even though abnormalities were noted on DPOAE and CRA testing, the interrupted speech and speech recognition in noise tests were the more sensitive tests for styrene effects. Further research is needed on the underlying mechanisms to understand the effects of styrene and on audiological test batteries to detect changes in populations exposed to solvents.

Audiometric findings in workers exposed to low levels of styrene and noise.

Audiometry and exposure measurements were conducted on workers from fiberglass and metal products manufacturing plants and a mail distribution terminal (N = 313). Workers exposed to noise and styrene had significantly worse pure-tone thresholds at 2, 3, 4, and 6 kHz when compared with noise-exposed or nonexposed workers. Age, noise exposure, and urinary mandelic acid (a biologic marker for styrene) were the variables that met the significance level criterion in the multiple logistic regression. The odds ratios for hearing loss were 1.19 for each increment of 1 year of age (95% confidence interval [CI], 1.11-1.28), 1.18 for every decibel >85 dB(A) of noise exposure (95% CI, 1.01-1.34), and 2.44 for each millimole of mandelic acid per gram of creatinine in urine (95% CI, 1.01-5.89). Our findings suggest that exposure to styrene even below recommended values had a toxic effect on the auditory system.