Fig 1.
Cochlear microphonic recordings for each subject made intraoperatively via the cochlear implant showing the large variability in responses.
Total amplitude of the responses ranged from ~5 μV to over 200 μV (blue line). Light grey area shows the noise floor. The subject ID in each axis is coloured according to the group categorisation (green = Growth, yellow = Fluctuating, red = Total Loss, see also Fig 5).
Fig 2.
3D visualization of cochlea and electrode position from subject ID 28, showing a potential soft contact with the basilar membrane and some slight buckling in the middle part of the array.
Fig 3.
ID 24 (Scala tympani without touching the basilar membrane, relatively deep insertion in a small cochlea); ID 27 (translocation of MidScala array); ID 28 (soft contact with the basilar membrane and some slight buckling in the middle part of the array); ID 35 (good position, little less than full insertion).
Fig 4.
Median hearing loss, calculated as the difference between pre-operative hearing and 4 weeks post-surgery, at each frequency for 47 subjects.
Fig 5.
Cochlea microphonic waveform examples for each of the Growth (n = 11), Fluctuating (n = 25) and Total loss (n = 4) groups and the threshold calculations used to define them.
Fig 6.
Average low frequency hearing loss after 4 weeks for the three groups of subjects categorized by the intraoperative cochlear microphonic amplitude.
Table 1.
Correlation analysis between several intra-operative measures and audiometric/outcome measures.
Amax is the maximal CM amplitude during insertion. Amin is the minimal CM amplitude after Amax. Aend is the final CM amplitude at the end of insertion. Low frequency HL is the average (125 Hz– 1.5 kHz) increase in thresholds 4 weeks after surgery compared to pre-operative.
Fig 7.
Cochlear Microphonic amplitude (blue) and phase (red) over insertion time.
The top panel shows a Type I example where the amplitude does not drop by more than 5 dB. In the middle panel (Type II) each drop is accompanied by large phase changes. The insertion in the lower panel is classified as Type III because the two drops around an insertion time of 100 s don’t come with significant phase changes.
Fig 8.
Average low frequency hearing loss after 4 weeks for the three groups of subjects with no drop > 5 dB (Type I), a drop > 5 dB with concurrent phase shift (Type II) and a drop > 5 dB without concurrent phase shift (Type III).