Brainstem Evoked Response Audiometry via Bone Conduction: The Clinical Assessment of Conductive Hearing Losses
Background To prevent a delay in the speech and/or language development of a child, early diagnosis of a hearing loss is crucial. Since it can be difficult to administer pure tone audiometry (PTA) in young children, brainstem evoked response audiometry (BERA) is often used. In this field, a new type of stimulus was designed: the LS CE-Chirp. This stimulus not only compensates for the cochlear travelling wave delay, but also for the upward spread of excitation at higher levels, and an increased change of the cochlear neural delay with frequency at lower levels. Purpose The first aim of this study was to discern patients with a cognitive hearing loss from normal hearing people and patients with retrocochlear pathology in otoneurological measurements. The second aim was to examine how BERA and PTA thresholds correlate, using the LS CE-Chirp. Methods ABRs evoked by the LS CE-Chirp of 24 participants were analysed in this study. PTA was performed in octaves between 250 and 8000 HZ via AC without and with plug, and between 500 and 4000 Hz via BC without plug. BERA BB and NB measurements, at 1000 and 4000 Hz, were performed via AC and BC, without and with plug. BC BERA measurements were performed with the inverting electrode in retro- and pre-auricular position. The auditory brainstem thresholds and wave latencies were visually interpreted and defined by two independent clinicians. Results The results showed that for AC measurements, wave latencies were significantly longer in the condition with plug than in the condition without plug; but for BC measurements, there was no significant difference in wave latencies between the two conditions. The results did not show significant different interwave intervals between the two conditions. Besides, the wave latencies were significantly shorter in AC measurements than in BC measurements. The results also showed that there was no significant effect of electrode position on the latencies of the waves nor the interwave intervals. Furthermore, the results showed that, overall, the correlation coefficients represented moderate to strong effects. But, a correction factor is needed to predict PTA thresholds by BERA thresholds, at 1000 and 4000 Hz in both AC and BC measurements. The correction factors for the combined data in this study, at 1000 Hz (p = .797b) and 4000 Hz (p =.801b) in AC measurements are recommended for the use in clinical practice. Conclusion The findings showed that BC measurements can discern patients with a conductive hearing loss from normal hearing people and patients with retrocochlear pathology. In addition, the findings showed that BERA thresholds can accurately predict PTA thresholds when a correction factor is used.
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