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Determination of coupling quality in round window vibroplasty with a newly developed, hand-held measuring probe
18 April 2018 (online)
One problem with round-window vibroplasty is that, after the FMT is inserted into the round-window niche, an assessment of the contact of the FMT with the round window membrane and thus the effectiveness of the transmitted vibrations into the inner ear is given by limited visual and tactile information on the FMT, only. Therefore, a hand-held measuring probe was developed, which analyzes the vibration of the stapes footplate to determine the cochlear excitation. In temporal bone experiments, the measuring accuracy of the probe was tested.
In five unfixed temporal bones a FMT was coupled to the round window membrane. After acoustic excitation with different sound pressures (0 dB, 80 dB, 94 dB, 106 dB, 115 dB), the deflections of the footplate were recorded in parallel by Laser Doppler Vibrometry (LDV) and the measuring probe.
The probe allowed for a clear differentiation of the coupling quality. The measured footplate vibrations from the excitation levels of 106 dB (and 115dB) were statistically significant compared to the testing without excitation (1.04 mV vs. 17.80 mV; p < 0.0001). The footplate deflections determined by LDV had the same order, but shifted to slightly higher absolute values.
The newly developed measuring probe in principle allows for measuring the quality of retrograde cochlear excitation in a round-window vibroplasty by hand-held contact with the footplate.