Physiological Assessment of Active Middle Ear Implant Coupling to the Round Window in Chinchilla lanigera

Objective. To study the effects of various active middle ear implant loading parameters on round window stimulation in an animal model. Study Design. Physiological measurements of the cochlear microphonic and stapes velocity were made from active middle ear implant–generated sinusoidal stimuli with controlled changes in loading parameters. Setting. Prospective study at an academic research institution. Subjects and Methods. Cochlear microphonic and stapes velocities (H EV ) were measured in 6 study subjects (Chinchilla lanigera) in response to active middle ear implant (Otologics MET, Boulder, Colorado) round window stimulation with assessment of effects of varying parameters of loading pressure, interposed connective tissue, and angle of stimulation with respect to the round window membrane. Results. The measured performance variabilities in repeated applications of the active middle ear implant to the round window were 2.5 dB and 5.0 dB for H EV and cochlear microphonic thresholds, respectively. Loading pressure applied to the round window (51-574 dynes) and angle of approach (±30° with respect to coronal plane) did not have a significant effect on cochlear microphonic thresholds or H EV . Significant improvements in cochlear microphonic thresholds and H EV were observed for interposed connective tissue regardless of tissue type. Conclusion. Variability in performance due to repeated couplings of the active middle ear implant to the round window is small and reproducible. Interposition of connective tissue significantly improves vibration energy transfer to the cochlea. Neither changes in loading pressure nor angle of stimulation of the round window affected active middle ear implant performance.