Round window stimulation with the floating mass transducer at constant pretension

Mechanical stimulation of the round window (RW) of the cochlea is successfully done with the Vibrant Soundbridge (Med-El), but clinical outcomes show a substantial degree of variability. One source of variability is variation in the static force applied by the stimulator to the round window (Maier et al., 2013). In this study we investigated other sources of variability by maintaining a constant pre-load testing the effect of a coupler device and the interposition of soft tissue between the stimulator and the RW.

Experimental.

The stapes footplate displacement produced by stimulation of the round window was determined in fresh human temporal bones. The response to sound and actuator stimulation was measured with a Laser Doppler Velocimeter at the stapes footplate. The RW was stimulated by a Floating Mass Transducer (FMT) with/without (1) an additional RW coupler (supplied by the manufacturer), and (2) the interposition of TUTOPATCH between the stimulator and the RW, while maintaining a pre-load of ∼1.96 mN.

In 8 temporal bones with normal stapes footplate response to sound, we found an average 11.9 dB increase (500 Hz-2 kHz) under controlled conditions by using the coupler together with the interposition. The increase was statistically significant at 500 Hz (p < 0.01). Additionally, the coupler/interposition combination reduced the variability between experiments (FMT alone SD = 10.9 dB; FMT with TUTOPATCH & coupler: SD = 3.4 dB @ 500 Hz) and increased the repeatability.

At controlled static force an improved output level, inter-subject variability and repeatability were found by using a coupler/TUTOPATCH combination in RW stimulation with the FMT. The high variability found in clinical experience is not solely due to inter-subject variability, but to coupling conditions and can be optimized further.