Conditions for highly efficient and reproducible round-window stimulation in humans.

Round-window stimulation is a new clinical approach for the application of active middle-ear implants. To investigate factors influencing the efficiency of round-window stimulation, experiments in 6 human temporal bones were performed with different actuator geometries and coupling conditions. The experiments show that the amplitude ratio between stapes and round-window actuator vibration is most efficient when using a 1.0-mm diameter rod with a 30° inclined tip geometry and an attached silicone pad. In this case, the amplitude ratio is 0.34 for frequencies up to 1.5 kHz and 0.27 for frequencies up to 20 kHz, with a standard deviation of only 4-6 dB at most frequencies. The analysis of data presented here and in a companion paper suggests that control of proper round-window membrane pretension as well as the inclined tip geometry are the major requirements for maximal performance.