Active middle ear implants-Enhanced efficiency of oval window stimulation with larger piston size

Direct piston-stimulation of the oval window with a middle ear implant, following a stapedotomy or stapedectomy, is one treatment option for patients with otosclerosis. Here, we experimentally investigated whether increasing the surface area of the actuated piston enhances transmission efficiency in oval window (OW) stimulation.

Fresh-frozen human cadaveric temporal bones (N = 14) were used to evaluate the output of different oval window couplers (OWCs) of A = 0.38 mm², 1.26 mm², 3.06 mm² by intracochlear pressure difference measurements between scala vestibuli (P_SV) and scala tympani (P_ST). Following stapedectomy, a piezoelectric transducer was used for OWC actuation. Additionally, a numerical model was also developed to estimate the output of the floating mass transducer (FMT, MEDEL, Austria).

Across frequencies, the average pressure difference was 18 and 8 dB higher for the large and medium OWC compared to the small OWC, respectively. Statistical analyses showed significant differences (p < 0.05) between piston diameters across most frequencies. Numerical simulation results using the volume displacement at the OW showed smaller output differences from 0.3 to 10 kHz, indicating that leakage at open gaps after stapedectomy has to be taken into account.

Our findings confirm that, for active stimulation with an actuator, increasing the surface area of the OWC enhances output efficiency proportionally. Nevertheless, volume leakage at open gaps to the OW may contribute additionally.