The Impact of a Cochlear Implant Electrode Array on the Middle Ear Transfer Function.

OBJECTIVES: As a treatment for partial deafness with residual hearing in the lower frequency range, the combined acoustic and electric stimulation of the cochlea has become widespread. Acoustic stimulation is provided by a hearing aid's airborne sound and the electric stimulation by a cochlear implant electrode array, which may be inserted through the round window or a cochleostomy. To take advantage of that concept, it is essential to preserve residual hearing after surgery. Therefore, the intracochlear electrode array should not compromise the middle ear vibration transmission. This study investigates the influence of different electrode types and insertion paths on the middle ear transfer function and the inner ear fluid dynamics. DESIGN: Sound-induced oval and round window net volume velocities were calculated from vibration measurements with laser vibrometers on six nonfixated human temporal bones. After baseline measurements in the "natural" condition, a cochleostomy was drilled and closed with connective tissue. Then, four different electrode arrays were inserted through the cochleostomy. Afterwards, they were inserted through the round window while the cochleostomy was patched again with connective tissue. RESULTS: After having drilled a cochleostomy and electrode insertion, no systematic trends in the changes of oval and round window volume velocities were observed. Nearly all changes of middle ear transfer functions, as well as oval and round window volume velocity ratios, were statistically insignificant. CONCLUSIONS: Intracochlear electrode arrays do not significantly increase cochlear input impedance immediately after insertion. Any changes that may occur seem to be independent of electrode array type and insertion path.

Acoustic Properties of Collagenous Matrices of Xenogenic Origin for Tympanic Membrane Reconstruction.

HYPOTHESIS: The acoustic properties of scaffolds made from decellularized extracellular cartilage matrices of porcine origin are comparable to those of the human tympanic membrane. BACKGROUND: Currently, the reconstruction of tympanic membrane in the context of chronic tympanic membrane defects is mostly performed using autologous fascia or cartilage. Autologous tissue may be associated with lack of graft material in revision patients and requires more invasive and longer operative time. Therefore, other materials are investigated for reconstruction. An increasingly important role could be played by scaffolds from different materials, which are known to induce constructive tissue remodeling. METHODS: To analyze the acoustic properties, the vibrations of the scaffolds, cartilage, perichondrium and tympanic membrane were measured by laser scanning doppler vibrometry under different static pressures. RESULTS: The analysis of volume velocities serves as an indicator for sound transmission. The results of the average volume velocities at atmospheric pressure show a similar frequency response of the tympanic membrane and the scaffolds with a peak at about 800 Hz. After changing the artificial ear-canal pressure from atmospheric pressure to negative pressure (-100, -200, and -300 daPa) the vibration characteristics of the different membranes remain fairly constant, whereas the results of the perichondrium show a decrease after changing the pressure into the negative range in the frequencies 1 to 3 kHz. CONCLUSION: The present study showed that the vibration characteristics of the scaffolds under atmospheric and negative pressure can be interpreted as similar to those of thin cartilage (<0.5 mm) and human tympanic membranes. However, in relation to the behavior of these scaffolds made from decellularized extracellular cartilage matrices in vivo, further investigations should be carried out.