ABR amplitude and dispersion variables. Relation to audiogram shape and click polarity

ABR amplitude behaviour to condensation (C) and rarefaction (R) clicks was investigated in normal ears, ears affected by Ménière's disease and ears with high-frequency hearing loss (HF ears). The wave IV-V amplitude-intensity function was steeper in ABRs evoked by R than by C clicks. This may suggest that two different cochlear generator components, one intensity-dependent as well as one polarity-dependent, contribute to click-evoked ABRs. Wave IV-V amplitude was significantly higher in Ménière ears compared to HF ears in spite of comparable 2-4 kHz hearing loss in the two groups. Hence, audiometric steepness (which is lower in Ménière ears than in HF ears) seems to predict the wave IV-V amplitude decline more precisely than the 2-4 kHz perception threshold. The wave IV-V dispersion variable (SR IV-V) was close to normal in Ménière ears, while wave IV-V was more dispersed in HF ears. In general, C click ABRs were less affected than R click ABRs by 'peripheral' factors (i.e. intensity and audiometric steepness).