The relationship between round window and ear canal Cochlear microphonic

HYPOTHESIS: Cochlear microphonic recorded at ear canal (CM‐EC) can be a substitute for the one recorded at round window (CM‐RW). BACKGROUND: Almost all clinics do not measure tone‐burst evoked CM due to technical difficulty although it can provide more information than click evoked CM. Moreover, clinicians like the CM‐EC more than that measured at CM‐RW because CM‐EC is non‐invasive. There is difference between CM‐RW and CM‐EC, for example, CM‐EC is less prominent than CM‐RW, therefore, studying tone‐burst evoked CM‐EC and its relationship with CM‐RW are highly significant and can promote the clinical application of CM‐EC. METHOD: Nine guinea pigs were randomly allocated into three groups, group 1 was not exposed to noise, called normal control. group 2 and group 3 were exposed to the low‐ (0.5–2 kHz) and high‐frequency band‐noise (6–8 kHz) at 120 dB SPL for 1 h, respectively. It was difficulty to record low‐frequency CM due to severe environmental interruption, in current study the recording technology of tone‐burst evoked CM was optimized so that tone‐burst evoked CM was measured across full speech frequency (0.5–8 kHz) in the presence of normal hearing and noise induced hearing loss (NIHL). RESULTS: CM‐RW and CM‐EC were successfully recorded across speech frequency. Significant reduction in CM amplitude was observed at 0.5 and 2 kHz in group 2, at 6 and 8 kHz in group 3 as compared to group 1, p < .05, indicating that CM amplitude was sensitive to band‐noise exposure. Significant correlation between CM‐RW and CM‐EC was also verified, p < .05. CONCLUSION: CM‐EC is a useful objective test for evaluation of hearing function; the result of current study supports the clinical application of non‐invasive CM‐EC.