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

Evaluation of noise-induced hearing loss by auditory steady-state and auditory brainstem-evoked responses

OBJECTIVES

Noise-induced hearing loss (NIHL) may result from occupational noise exposures and is considered as an 'Occupational Disease'; therefore, it is compensable. To verify the existence and severity of the work-related hearing loss, there is a need of an objective, reliable auditory measure in cases of arbitration of financial disputes to resolve any medicolegal aspects. The objective of the study was to compare between the ABR and ASSR for predicting the behavioural threshold in subjects with normal hearing or NIHL.

DESIGN

The study included 82 subjects regularly exposed to high levels of occupational noise, with normal hearing and NIHL. ABR to clicks and to tone bursts were recorded followed by multiple-frequency ASSR. Physiological and behavioural thresholds were compared for specific frequencies (1000, 2000 Hz) and average of high-frequency range (2000 and 4000 Hz). In addition, Pearson correlations and the specificity and sensitivity of each measure were also calculated using receiver operating characteristic (ROC) curves.

RESULTS

In the NIHL group, there was a significantly smaller difference between the behavioural threshold and click-ABR than the ASSR in high-frequency range. Pearson correlations were significantly higher for click-ABR. Analysis of specific frequencies yielded a smaller difference between behavioural and ASSR than tone-burst-ABR thresholds, with a slightly better correlation for ASSR than tone-burst-ABR. Higher sensitivity but lower specificity was suggested for ASSR than ABR.

CONCLUSIONS

ASSR is associated with high-frequency specificity, shorter test sessions and good correlations with behavioural thresholds, making it a potentially better measure than ABR for predicting audiograms in subjects with NIHL. These findings have diagnostic implications, especially in cases of workers' compensation when subjects may be uncooperative.

Hearing threshold estimation by auditory steady-state responses with narrow-band chirps and adaptive stimulus patterns: implementation in clinical routine

Objective hearing threshold estimation by auditory steady-state responses (ASSR) can be accelerated by the use of narrow-band chirps and adaptive stimulus patterns. This modification has been examined in only a few clinical studies. In this study, clinical data is validated and extended, and the applicability of the method in audiological diagnostics routine is examined. In 60 patients (normal hearing and hearing impaired), ASSR and pure tone audiometry (PTA) thresholds were compared. ASSR were evoked by binaural multi-frequent narrow-band chirps with adaptive stimulus patterns. The precision and required testing time for hearing threshold estimation were determined. The average differences between ASSR and PTA thresholds were 18, 12, 17 and 19 dB for normal hearing (PTA ≤ 20 dB) and 5, 9, 9 and 11 dB for hearing impaired (PTA > 20 dB) at the frequencies of 500, 1,000, 2,000 and 4,000 Hz, respectively, and the differences were significant in all frequencies with the exception of 1 kHz. Correlation coefficients between ASSR and PTA thresholds were 0.36, 0.47, 0.54 and 0.51 for normal hearing and 0.73, 0.74, 0.72 and 0.71 for hearing impaired at 500, 1,000, 2,000 and 4,000 Hz, respectively. Mean ASSR testing time was 33 ± 8 min. In conclusion, auditory steady-state responses with narrow-band-chirps and adaptive stimulus patterns is an efficient method for objective frequency-specific hearing threshold estimation. Precision of threshold estimation is most limited for slighter hearing loss at 500 Hz. The required testing time is acceptable for the application in everyday clinical routine.