Experiments on tympanic membrane reconstruction influencing the middle ear transfer function after middle ear reconstruction with the 'Vibrant-Soundbridge'-simulation of reduced middle ear ventilation

Introduction:

The middle ear transfer function should be measured in a temporal bone study after vibroplasty on the stapes head and under simulation of atmospheric pressure fluctuations (pressurization via external ear canal). Subsequently, materials used for tympanic membrane reconstruction (sheep ear cartilage varying in thickness, perichondrium, 3-D printed tympanic membrane models) were analyzed on their material properties.

Methods:

Middle ear transfer function of 10 temporal bones was measured using LDV in a multi-stage trial. Maximum pressure applied on the external meatus was +3 kPa. Materials used for tympanic membrane reconstruction were evaluated using LDV, optical coherence tomography (OCT), Doppler OCT and Micro-CT.

Results:

Under normal pressure conditions, transmission behavior was independent of the material's stiffness. Under pressure, maximum transmission loss at low frequencies was 20 dB for elastic material and 5 dB for stiff material. At high frequencies, measured loss was 5 – 10 dB and independent of the material's stiffness.

Conclusions:

The stiffer the reconstruction material, the lower its displacement under pressure and the lower pressure induced stiffening effects in the direction of the vestibulum (e.g. stiffening of the annular ligament). Stiffening-induced transmission losses are mainly found at low frequencies and cannot be compensated by the FMT in this range. Above of 1300 Hz, the continuous force range of the FMT acts against transmission losses, being independent of the material's stiffness. To minimize postoperative pressure-fluctuation-induced transmission loss, choosing a tympanic membrane reconstruction material with a high stiffness seems to be appropriate, cartilage stiffness can be varied intraoperative by varying its thickness.

Publikationsverlauf

Publikationsdatum:
18. April 2018 (online)