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Can Middle Ear Dysfunction Affect Cochlear Implant Function?

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Abstract

This poster is a retrospective case review of a pediatric cochlear implant recipient for whom changes in electrode impedances and auditory function were closely associated with changes in middle ear function.
Can Middle Ear Dysfunction Impact Cochlear Implant Function?
Jeffrey L. Simmons, M.A., CCC-A, Boys Town National Research Hospital, Omaha, NE
INTRODUCTION
Because a cochlear implant (CI) bypasses the
conductive component of the normal auditory
process, logic might suggest that a middle ear
problem cannot impact the function of a CI.
Anecdotal and scienti c evidence suggest that this
may not be the case. In ammatory processes in
the tissue of the inner ears of implant recipients
can result in increased electrode impedance values
1-3. This in ammation has been associated with
middle ear dysfunction in some cases 3. Impedance
indicates the amount of electrical resistance for a
stimulating electrode and the surrounding tissue.
When impedances increase between the active
and return electrodes, terminal voltage will increase
to maintain a constant charge. If the impedance
is too high, the terminal voltage could reach the
maximum supply voltage (compliance limit), and
it may become impossible to attain the desired
charge from the implant. The function of the CI
would consequently be affected (see Fig. 1). The
following is a retrospective case review of a pediatric
cochlear implant recipient for whom changes in
electrode impedances and auditory function were
closely associated with middle ear dysfunction.
Fig. 1 -- Cycle described by Neuberger et al. 3
in which a triggering event such as in ammation
might lead to a self-perpetuating problem with per-
formance of the CI. In this cycle, increased imped-
ances that cause some or all electrodes to reach
compliance limits result in asymmetries in the bi-
phasic stimulus pulses from the affected elec-
trodes. This can lead to electrolytic changes and
Platin dissolution that can increase impedances
even further.
Patient Characteristics:
Female, Age 3;8
Right Advanced Bionics HR90K at age 1;1
• Home schooled
Speech-language standard scores in the high
average range
• Concern for “overnight” change in auditory per-
formance at 2;6 post-implant (inconsist ability to
identify Ling sounds, uncharacteristic “self-talk”
and humming, frequent requests of needing to
change the battery, and generally listless behav-
ior as if she did not feel well).
CASE HISTORY
Figure 2: Baseline Performance (2 yrs., 1 mos. Post Implant)
Baseline
A: tympanogram
B: electrode impedances
C: map levels
D: behavioral audiogram with implant in use 4 months prior to the
rst parental report of changes in cochlear implant performance.
Figure 3: 1st Episode of Change in Auditory Behavior (2 yrs.,6 mos. Post Implant)
Figure 4: Resolution of Symptoms (One Month Later)
Figure 5: 2nd Episode of Changes in Auditory Behavior (Two Months Later)
Figure 6: Serial Impedances
Pattern of impedances across nearly four years.
Black boxes highlight occurrences of signi cantly
elevated impedances associated with possible
middle ear problems. Periodic impedance
measures since 2008 (not all shown) have all been
in the normal range with no signi cant increases.
There have been no further reported episodes of
uctuations in auditory performance and no known
episodes of middle ear dysfunction or effusion.
DISCUSSION
• Two transient episodes of changes in CI electrode
impedances and auditory performance apparently
associated with the occurrence of middle ear
dysfunction.
Neuberger et al.3 refer to increases in impedances
in implant recipients that occur in connection with
common colds. For 7 individuals, spontaneous
increases in impedances closely correlated in
time with in ammatory events believed to have
resulted from labyrinthitis were reported.
One possible explanation for the changing
impedances for the child in this case study might
be an in ammation in cochlear tissue triggered
by the presence of otitis media.
A possible cause could be pressure changes in the
middle ear from effusion that increases pressure
in the cochlea via the round window, which may
alter the position of the electrode array. When
the uid resolves, intracochlear pressure returns
to its normal state, and the electrode array moves
back to where it was formerly situated. However,
brous tissue growth around the array may
preclude this as a possible explanation.
• Another possible explanation would be that uid in
the middle ear changes the pathway of electrical
current generated by the implant.
Suggested protocol to address this issue:
• Regular monitoring of middle ear function and
electrode impedances, especially for young
children or poor self-reporters
ENT referral for antibiotic or anti-in ammatory
therapy
• Adjustment of implant stimulus levels if auditory
responses are affected
• Manual widening of stimulus pulsewidth or use
of Automatic Pulsewitdth II (APW II) to maintain
adequate loudness and remain within voltage
compliance limits
Creation of an “emergency” program for patients
with frequent or recurrent middle ear problems
and/or uctuations in auditory performance
REFERENCES
1. Clark, G.M, Fracs, S.A., Shute, M.B., Shepherd, R.K., Carter, T.D. (1995). Cochlear implantation:
Osteoneogenesis, electrode-tissue impedance, and residual hearing. Annals of Otology, Rhinology,
& Lanrygology, 104(Suppl. 166), 40-42
2. De Ceulaer, G., Johnson, Yperman, M., Daemers, K., Offeciers, F.E., O’Donoghue, G.M., Govaerts
(2003). Long-term evaluation of the effect of intracochlear sterioid deposition on electrode
impedance in cochlear implant patients. Otology & Neurology, 24, 769-774.
3. Neuburger, J., Lenarz, T., Lesinski-Schiedat, A., Büchner, A. (2009) Spontaneous increased in
impedance following cochlear implantation: Suspected causes and management. International
Journal of Audiology, 48, 233-239.
4. Tykocinski, M., Cohen, L.T., Cowan, R.S. (2005). Measurment and analaysis of access resistance
and polarization impedance in cochlear implant recipients. Otology & Neurotology, 26, 948-956.
ABCD
ABCD
ABCD
ABCD
A-B: Follow-up visit to the clinic one month after the middle ear
dysfunction was identi ed. Static admittance measured during
tympanometry and electrode impedances were more similar to the
baseline measures.
C: Map levels similar baseline.
D: The threshold for 250 Hz narrowband noise on the behavioral
audiogram showed an improvement of 35 dB even though stimula-
tion levels (M levels) were lower than one month earlier.
Recurrence of concerns for auditory performance and implant
function.
A: Static admittance on the typanogram was just within normal
limits but was reduced compared to the baseline obtained for the
child’s right ear.
B: Impedances for E 1-11 were elevated once more, and E 6 was
classi ed as an open circuit.
C-D: The behavioral audiogram for a newly created “emergency”
program intended for use immediately as well as in the event that
episodes of worsening auditory performance again. This program
featured increased M levels and deactivated E 6 due to the open
circuit for the electrode.
A: Compared to baseline, her tympanogram showed reduced
static admittance consistent with middle ear effusion, which was
medical diagnosis at the time.
B: Impedance values for E 1-11 were elevated relative to baseline
what is typically seen for the more recent generations of electrode
systems 4. Electrodes 5 and 6 were open circuits.
C: The modi ed map used for testing.
D: Even after increasing stimulation levels for the implant in
an attempt to restore an adequate perception of loudness, the
behavioral threshold for narrowband noise at 250 Hz was 25 dB
poorer than that measured 4 months previously, and the child
continued to have dif culty discriminating between or identifying the
phonemes /i/ and /u/. Formants for the Ling sounds (conversational
level) are plotted in terms of frequency and amplitude. Note how the
low-frequency phonemes may have had their audibility impacted
by the poorer threshold observed for 250 Hz.
AUTHOR CONTACT INFORMATION
Jeffrey Simmons, M.A., CCC-A
425 N. 30th St., Omaha, NE 68131
402-452-5040; Jeffrey.simmons@boystown.org
ResearchGate has not been able to resolve any citations for this publication.
Article
Modern cochlear implant systems deliver impulse transmission rates up to 50,000 pps. It emerged that the fast stimulation rates led to enhanced speech comprehension. Impedance measurement is an important aspect in cochlear implant testing procedures. Impedance values are a measure of the electrical resistance between the individual implant electrodes. Increased impedances were attributed frequently to inflammatory/tissue-related processes. In recent years, however, we have repeatedly found cases of impedance increase for which the inflammatory model did not provide a satisfactory explanation. The aim of this study is to evaluate increases in impedance in our cochlear implant population, to attempt to find their cause, and to formulate therapeutic hypotheses. In our cochlear implant programme (> 3000 recipients) we screened our database for impedance increases over time during device fitting. We found 16 patients with 18 affected ears in whom impedance increases were clearly demonstrated. We found that especially in cases without any sign of prior inflammation, increasing the pulse width of the stimulation strategy seems to be an effective tool to return increased impedances to normal levels.
Article
To evaluate the long-term effect of intracochlear steroid deposition on electrode impedance in patients with cochlear implants. A retrospective study was carried out comparing the impedances of cochlear implant electrodes with and without a single application of steroids in the cochlea. Ninety two implanted children with an average age of 5 years (range, 0.7 to 16 years) were divided in four groups according to the type of electrode and the use of steroids or not. In addition, the impedances of five children who required a reimplantation are reported. The impedances of Nucleus electrodes, either straight or Contour, were measured at regular intervals up to 12 months after surgery. Two months after surgery, the impedances in the steroid groups were significantly lower than in the nonsteroid groups (straight electrodes, 3.9 versus 4.7 kOhm, respectively; Contour electrodes, 5.4 versus 6.5 kOhm, respectively). This reduction remained stable over time for the straight electrodes, but for the Contour electrodes, it seemed to disappear after 6 months. The impedances after a second implantation were significantly higher than after a first implantation (median value, 8.8 kOhm after 2 months). The application of a single dose of a steroid solution reduces the electrode impedances significantly, and, for the straight electrodes, this effect seems to last. It seems justified to reimplant with caution, because this seems to increase the impedances substantially.
Article
Impedance measurements are commonly performed at the end of cochlear implant surgery, not only to confirm that all electrodes are working but also to monitor the impedances of the newly implanted electrodes. The current method of testing allows the determination of only the overall electrode impedance but not its components, access resistance and polarization impedance. To determine whether any longitudinal change in the electrode impedance is caused by a change in the endocochlear environment or rather caused by a change in the surface quality of the electrode, it is necessary to extract access resistance and polarization impedance. We applied an impedance model that enabled us to calculate access resistance and polarization impedance after measurement of electrode impedance at three points along the voltage waveform. The results show that the value of the components of electrode impedance varied with time after surgery: access resistance increased slowly over time, whereas polarization impedance increased up to Week 2 but decreased after commencement of electrical stimulation at that stage. These results are consistent with the hypothesis that a layer of fibrous tissue forms around the electrode within the cochlear canal, resulting in a slow increase of access resistance, whereas a layer of proteins forms on the surface of the electrode in the early phase after implantation. Electrical stimulation appears to disperse this surface layer, thereby reducing both the polarization impedance and electrode impedance. The method presented enables the extraction of more detailed information about the longitudinal changes in the intracochlear environment after cochlear implantation.