[A comparison of low-chirp- and notched-noise-evoked auditory brainstem response]

In order to obtain a low-frequency specific auditory brainstem response (ABR) there are less stimuli that plege a satisfying accordance with the ABR threshold and the behavioural threshold. This study investigates the so called low-chirp-ABR as to predict a low-frequency-amblyacousia and compares it to the notched-noise-500 Hz-ABR.

We evaluated behavioural and ABR thresholds to a low-chirp respectively a 500 Hz tone presented in notched noise masking from 32 patients with a severe hearing loss at low-frequencies and 28 patients with normal hearing.

The average difference ± single standard deviation between low-chirp-ABR and behavioural threshold is 1.53 dB ± 7.68 dB in the group of patient with low-frequency hearing loss and 2.55 dB ± 5.46 dB in the group of normal hearing. On the contrary the difference between notched-noise-500 Hz- and behavioural thereshold averages 2.67 dB ± 9.29 dB (low-frequency hearing loss) respectively 8.82 dB ± 7.90 dB (normal hearing). In order to verify the equivalence between the several methods we did a equivalence test that shows that low-chip-ABR and behavioural threshold can be considered as equal to obtain a low-frequency threshold. In contrast the comparison of notched-noise-500 Hz-ABR and behavioural threshold proves no equivalence.

We detected a significant equivalence between low-chirp-ABR and pure-tone audiometric. The ABR to a low-chirp stimulus seems to be rather precise in contrast to the notched-noise-500 Hz-evoked-ABR in order to diagnose a low-frequency-hearing loss.