Abstract
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.
Highlights
Hearing problems are not just a matter of reduced ability to recognize speech and other sounds, and of tinnitus, abnormal sensitivity to loud sound and sound distortion
Very rough estimates of noise exposure based on the individual responses to the questionnaire indicated that the groups Education and Other were significantly different from the groups Music and Industry by being judged less noise exposed (p,0.05)
Individuals having auditory problems and normal or near-normal hearing thresholds were divided into groups of subjects with similar noise exposure, and measured with advanced hearing tests
Summary
Hearing problems are not just a matter of reduced ability to recognize speech and other sounds, and of tinnitus, abnormal sensitivity to loud sound and sound distortion. The factor with the largest attributable risk was self-reported work-related noise exposure (almost 14%). The largest single factor was self-reported tolerable occupational noise exposure (9.3%). This means that a number of occupations with less noise burden than industrial exposure are at risk for noise-induced tinnitus. In occupations related to music the noise often varies around the sound level above which there is a risk of NIHL according to the international standardisation[8]. In other studies no relationship between music exposure and hearing loss, in terms of pure tone thresholds, has been found (for a review, see Zhao et al[11]). Tinnitus is common among rock/jazz musicians, when the audiogram is similar to that of a reference group not exposed to excessive music[12]
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