Dichotic multiple-frequency auditory steady-state responses in evaluating the hearing thresholds of occupational noise-exposed workers.

An objective, fast, and reasonably accurate assessment test that allows for easy interpretation of the responses of the hearing thresholds at all frequencies of a conventional audiogram is needed to resolve the medicolegal aspects of an occupational hearing injury. This study evaluated the use of dichotic multiple-frequency auditory steady-state responses (Mf-ASSR) to predict the hearing thresholds in workers exposed to high levels of noise. The study sample included 34 workers with noise-induced hearing impairment. Thresholds of pure-tone audiometry (PTA) and Mf-ASSRs at four frequencies were assessed. The differences and correlations between the thresholds of Mf-ASSRs and PTA were determined. The results showed that, on average, Mf-ASSR curves corresponded well with the thresholds of the PTA contours averaged across subjects. The Mf-ASSRs were 20±8dB, 16±9dB, 12±9dB, and 11±12dB above the thresholds of the PTA for 500Hz, 1,000Hz, 2,000Hz, and 4,000Hz, respectively. The thresholds of the PTA and the Mf-ASSRs were significantly correlated (r=0.77-0.89). We found that the measurement of Mf-ASSRs is easy and potentially time saving, provides a response at all dichotic multiple frequencies of the conventional audiogram, reduces variability in the interpretation of the responses, and correlates well with the behavioral hearing thresholds in subjects with occupational noise-induced hearing impairment. Mf-ASSR can be a valuable aid in the adjustment of compensation cases.

Predicting hearing thresholds and occupational hearing loss with multiple-frequency auditory steady-state responses.

OBJECTIVE: An objective investigation is needed to verify the existence and severity of hearing impairments resulting from work-related, noise-induced hearing loss in arbitration of medicolegal aspects. We investigated the accuracy of multiple-frequency auditory steady-state responses (Mf-ASSRs) between subjects with sensorineural hearing loss (SNHL) with and without occupational noise exposure. DESIGN: Cross-sectional study. SETTING: Tertiary referral medical centre. METHODS: Pure-tone audiometry and Mf-ASSRs were recorded in 88 subjects (34 patients had occupational noise-induced hearing loss [NIHL], 36 patients had SNHL without noise exposure, and 18 volunteers were normal controls). MAIN OUTCOME MEASURES: Inter- and intragroup comparisons were made. A predicting equation was derived using multiple linear regression analysis. RESULTS: ASSRs and pure-tone thresholds (PTTs) showed a strong correlation for all subjects (r = .77 ≈ .94). The relationship is demonstrated by the equationThe differences between the ASSR and PTT were significantly higher for the NIHL group than for the subjects with non-noise-induced SNHL (p < .001). CONCLUSIONS: Mf-ASSR is a promising tool for objectively evaluating hearing thresholds. Predictive value may be lower in subjects with occupational hearing loss. Regardless of carrier frequencies, the severity of hearing loss affects the steady-state response. Moreover, the ASSR may assist in detecting noise-induced injury of the auditory pathway. A multiple linear regression equation to accurately predict thresholds was shown that takes into consideration all effect factors.

Damage of white matter tract correlated with neuropsychological deficits in carbon monoxide intoxication after hyperbaric oxygen therapy.

Carbon monoxide (CO) intoxication can result in cognitive deficits and demyelinating changes of the white matter (WM), for which hyperbaric-oxygen (HBO) treatment is considered effective in reducing neuropsychiatric symptoms. This study aimed to analyze cognitive functions and WM diffusion properties in CO intoxication after standard HBO treatment. Seventeen CO intoxicated patients were evaluated 4-6 months after HBO treatment. They also underwent diffusion tensor imaging (DTI) and cognitive assessment, and the results were compared with those from 34 age-matched controls. DTI was transformed into fractional anisotropy (FA) and mean diffusivity (MD) and assessed at every voxel level with tract-based spatial statistics across the brain. Correlation between reduced FA and increased MD with neuropsychological deficits were performed. Cognitive results showed that impairment in executive function, as well as verbal and visual memories, were most prominent. There were extensive areas of increased MD and decreased FA. Correlation analyses showed that memory retrieval, judgment, and verbal generation tasks were related to FA of the frontotemporal WM. MD showed weaker correlation with cognitive deficits. These data suggest that neurologic deficits and WM changes are detectable 4-6 months after HBO therapy. The correlation of WM diffusion with cognitive deficits also suggests that reduced connectivity between different cortical regions is a pathophysiologic mechanism.