Air- and Bone-Conducted Sources of Feedback With an Active Middle Ear Implant.
Renee M Banakis Hartl, James R Easter, Mohamed A Alhussaini and 2 others
PMID 30199397WHAT IT FOUND
In cadaver ears, the implant's mounting bracket increased ear-canal sound by 5 to 10 dB and bone-conducted vibration at higher frequencies.
The study did not test whether damping reduces feedback in patients.
Key findings
01Ear-canal sound pressure from the implant ranged from 40 to 80 dB SPL and peaked around 2 kHz, and from 40 to 85 dB SPL and peaked at 700 and 2000 Hz.
02The mounting bracket added 5 to 10 dB to ear-canal sound pressure below 2 kHz, and the paper reported significant differences at 500 Hz and at 594.6, 707.1, 840.9, and 1189 Hz.
03At 1.0 V, bone-conducted velocity varied by recording location across frequencies and by bracket coupling in high frequencies.
STILL TO COME
How it was doneWhat they found
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What it does not show
The study used cadaveric heads, so living tissue properties and patient hearing responses were not represented. Only four ears were tested, which limits confidence in the statistical comparisons. The device microphone was not used to measure actual feedback, so the study did not show that the recorded signals would cause whistling in patients. Single-axis laser Doppler vibrometry did not capture three-dimensional head motion from bone conduction. Cadaveric specimens may have post-mortem degradation and lack intracranial structures and fluid. The probe tube may have touched the ear-canal wall, which could overestimate air-conducted measurements.
Declared interests
The authors declared no conflicts of interest. The article is listed as NIH extramural research support.
The easy way to misread this
Do not read the 5 to 10 dB increase as proof that patients will get less feedback after bracket damping. The study measured sound and vibration in cadaver ears, not actual feedback through the implant microphone in patients.