The influence of inner ear impedance on middle ear sound transfer functions

Introduction For experimental studies of middle ear transfer function (METF), it may be advantageous to perform the measurements without the inner ear. In this case, it is important to know the influence of inner ear impedance on METF. Previous studies provide contradictory results in this regard. With the current study, we would like to investigate the influence of inner ear impedance in more detail and find possible reasons for deviations in the previous studies.

Methods 11 fresh frozen temporal bones were prepared in our study. After measuring the intact specimen as a reference (step1), the round window membrane was punctured (step2), then totally removed (step3). The cochleostomy was performed (step4) before the cochlea fluid carefully suctioned through scala tempani (step5) and scala vestibuli (step6). Finally the cochlear was completely removed (step7). Translational and rotational movement of the stapes footplate were measured and calculated. The results of the steps were compared to quantify the effect of subsequently draining the cochlea.

Results As the inner ear impedance decreases at each step, the amplitudes of the METF curves gradually increase at higher frequencies. At step6, the measured METFs are significantly different respect to the intact group for frequencies above 3 kHz. The differences are frequency dependent. Stronger influence occurs at the high frequencies. Significant decrement of rotational motions appears at frequencies above 4.5 kHz at step5.

Conclusion This study confirms the influence of inner ear impedance on METF only at higher frequencies (>= 3 kHz). Study results that found no influence of cochlea impedance may be due to incomplete drainage of the cochlea.

China Scholarship Council

Publication History

Article published online:
12 May 2023