 |
|
Effects of the Clarion Electrode Positioning System on Auditory Thresholds and Comfortable Loudness Levels in Pediatric Patients With Cochlear Implants
Gail S. Donaldson, PhD;
Michael D. Peters, MD;
Melisa R. Ellis, MA;
Barbara J. Friedman, MS;
Samuel C. Levine, MD;
Franklin L. Rimell, MD
Arch Otolaryngol Head Neck Surg. 2001;127:956-960.
ABSTRACT
| |
Objective To evaluate the effects of using the Electrode Positioning System on
psychophysical auditory thresholds, most comfortable loudness levels, and
electric auditory brainstem response (EABR) thresholds in children with the
Clarion version 1.2 cochlear implant.
Design Retrospective analysis.
Setting Academic tertiary care center.
Patients and Methods Clinical records of a series of 25 children who received the Clarion
version 1.2 cochlear implant at the University of Minnesota, Minneapolis,
between January 1997 and August 1999 were examined. Measures evaluated were
psychophysical thresholds (T-levels) and most comfortable loudness levels
(M-levels) obtained at the 3-month posthookup audiologic evaluation and EABR
thresholds obtained during implant surgery. Relevant threshold measures were
available for 24 patients, 11 of whom had received the Clarion spiral electrode
and electrode positioner (EP group) and 13 of whom had received the spiral
electrode without positioner (non-EP group). The 3 measures (T-levels, M-levels,
and EABR thresholds) were compared across groups. In addition, EABR thresholds
were compared with T-levels and M-levels within groups.
Results Mean T-levels and M-levels were significantly lower for the EP group
than for the non-EP group, and interpatient variability for these measures
was considerably smaller in the EP group. Electric auditory brainstem response
thresholds were not significantly different for EP vs non-EP patients; however,
EABR data were available for only a few non-EP patients.
Conclusions Use of the electrode positioner results in lower T-levels and M-levels
in children with the Clarion version 1.2 cochlear implant, consistent with
results of previous studies in adults, and reduces across-patient variability
for these measures. It is unclear from the present data whether use of the
electrode positioner systematically reduces intraoperative EABR thresholds.
INTRODUCTION
IN 1998, Advanced Bionics Corporation (Sylmar, Calif) introduced the
Electrode Positioning System or "positioner" for use with its Clarion version
1.2 perimodiolar, spiral electrode. The positioner is a wedge-shaped piece
of Silastic that is inserted lateral to the spiral electrode in the scala
tympani. It is designed to move the electrode array medially toward the modiolar
wall of the cochlea, thereby placing electrode contacts closer to residual
auditory neurons. Clinical studies in adults have shown that using the positioner
reduces electrical auditory thresholds and comfortable loudness levels1-3 and increases electrode
insertion depth.2
The primary purpose of the present study was to evaluate the effects
of using the electrode positioner on psychophysical thresholds (T-levels)
and most comfortable loudness levels (M-levels) in pediatric patients with
the Clarion version 1.2 prosthesis. It was expected that, similar to findings
in adults, T-levels and M-levels would be lower in patients who have the positioner
compared with those who have the spiral electrode alone. Secondary goals of
the study were to compare electric auditory brainstem response (EABR) thresholds
for positioner and nonpositioner patients and to compare EABR thresholds with
T-levels. Some EABR analyses were limited by the small number of nonpositioner
patients for whom EABR data were available.
PATIENTS AND METHODS
Clinical records were examined for a consecutive series of 25 children
who underwent surgical implantation of the Clarion version 1.2 cochlear prosthesis
at the University of Minnesota, Minneapolis, between January 1997 and August
1999 (Table 1). Relevant psychophysical
measures or EABR thresholds were available for 24 of these patients. Eleven
patients underwent implantation with the Clarion spiral electrode and electrode
positioner (EP group), whereas the remaining 13 underwent implantation with
the spiral electrode alone (non-EP group). Mean (SD) ages of the non-EP and
EP groups were 3.2 (1.1) and 4.2 (1.9) years, respectively.
|
|
|
|
Characteristics of 24 Children Who Underwent Implantation of the Clarion
Version 1.2 Cochlear Spiral Electrode*
|
|
|
The Clarion spiral electrode has 16 intracochlear electrodes arranged
in 8 medial-lateral pairs. All measures in the present study were obtained
for the 8 medial electrodes coupled in monopolar mode to a return electrode
on the case of the internal receiver-stimulator. Full insertion of the electrode
array was achieved in all patients.
The Clarion device supports several speech-processing strategies, including
an analog strategy (simultaneous analog stimulation) and an interleaved pulsatile
strategy (continuous interleaved sampler). Most patients in our series were
initially programmed in the continuous interleaved sampler strategy. For this
reason, T-levels and M-levels were taken from continuous interleaved sampler
speech-processing programs established at patients' 3-month posthookup audiologic
evaluations. The 3-month point was selected because T-levels and M-levels
generally stabilize within 3 months of hookup and because 3-month measures
were available for 22 of 24 patients in our sample. The T-levels were obtained
with a descending method of limits procedure using Clarion clinical programming
software. The M-levels were not measured directly but were established during
the first 3 months of device use by progressively raising M-level settings
to the maximum levels that were well tolerated by the patient. Psychophysical
stimuli were 50-millisecond trains of biphasic pulses with a pulse rate of
approximately 800 pulses per second (pps) and a pulse duration of 75 µs/phase.
Electric auditory brainstem responses were recorded in the operating
room after surgical implantation of the electrode and receiver-stimulator.
Stimuli for EABR recordings were single 75-µs/phase biphasic pulses
presented at a pulse rate of 10 pps to 21 pps. Responses were recorded differentially
between vertex (+) and nape (-) electrodes using a noncephalic ground
electrode. Threshold was specified as the lowest current amplitude (in clinical
units [CU]) at which a repeatable wave V could be visually identified in the
traces. Threshold estimates were typically based on 2 waveform recordings
per current level, each composed of averaged responses to 500 stimulus repetitions.
The EABR data were excluded if recordings were excessively noisy or if electrode
impedances exceeded 20 k at the time of testing. Because recording
conditions were suboptimal for many of the earlier (non-EP) patients in the
series, acceptable EABR measures were available for only 4 patients in the
non-EP group.
Electric auditory brainstem response recordings were not available for
the same electrodes in all patients. Generally, recordings existed for 1 apical
electrode (electrode 1 or 2), 1 or 2 middle electrodes (electrodes 3, 4, or
5), and 1 basal electrode (always electrode 7). To facilitate comparisons
across patients, electrodes 1 and 2 were combined into an "apical" electrode
group and electrodes 3, 4, and 5 were combined into a "middle" electrode group.
When data were available for 2 middle electrodes in a given patient, the 2
threshold estimates were averaged, resulting in a single EABR threshold for
the middle electrode.
RESULTS
PSYCHOPHYSICAL THRESHOLDS
There was considerable overlap in the T-levels of EP and non-EP patients
(Figure 1 and Figure 2). Mean thresholds were significantly lower for EP patients
than for non-EP patients on electrodes 1 through 7 (P<.02,
Mann-Whitney test), but differences were not statistically significant for
electrode 8, the most basal electrode. Average thresholds across all 8 electrodes
were 154 CU for the non-EP group and 86 CU for the EP group. Thus, mean T-levels
were 68 CU lower in the EP group. Across-patient variability in threshold
measures was considerably larger for non-EP patients than for EP patients,
primarily because 2 patients in the non-EP group (patients 3 and 7) demonstrated
unusually high thresholds (Figure 1).
Thresholds did not vary systematically as a function of electrode number in
non-EP patients; however, for EP patients, thresholds for electrodes 7 and
8 were significantly higher than those for electrodes 1 through 6.
|
|
|
|
Figure 1. Psychophysical thresholds (T-levels)
for individuals who received the Clarion spiral electrode and electrode positioner
(EP group) or the spiral electrode without positioner (non-EP group) as a
function of electrode number. Low electrode numbers correspond to more apical
electrodes; high electrode numbers, to more basal electrodes.
|
|
|
|
|
|
|
Figure 2. Mean psychophysical thresholds
(T-levels) for patients who received the Clarion spiral electrode and electrode
positioner (EP group) or the spiral electrode without positioner (non-EP group)
as a function of electrode number. Error bars indicate 1 SD.
|
|
|
Excluding the data for the 2 outliers in the non-EP group reduced the
mean threshold for this group to 115 CU and resulted in a mean threshold difference
of 29 CU between the EP and non-EP groups (Figure 2). Mean thresholds for the modified non-EP group were still
significantly higher than those for the EP group for electrodes 1 through
6 but were not significantly different than mean EP thresholds for electrodes
7 or 8. The modified non-EP group demonstrated similar interpatient variability
in T-levels as the EP group.
MOST COMFORTABLE LOUDNESS LEVELS
Findings for M-levels were similar to those described for T-levels.
Again, there was considerable overlap in M-levels for EP and non-EP patients,
but variability was much greater for the non-EP group (Figure 3 and Figure 4).
Mean M-levels were significantly lower for EP patients than for non-EP patients
on all electrodes except electrode 7 (P<.02, Mann-Whitney
test). Average M-levels were 292 CU for the EP group and 506 CU for the non-EP
group. Thus, mean M-levels were 214 CU lower in the EP group. The M-levels
did not vary systematically as a function of electrode number for non-EP patients;
however, for EP patients, thresholds for the most basal (highest number) electrodes
were significantly higher than those for the most apical (lowest number) electrodes
(P<.05).
|
|
|
|
Figure 3. Most comfortable loudness levels
(M-levels) for individuals who received the Clarion spiral electrode and electrode
positioner (EP group) or the spiral electrode without positioner (non-EP group)
as a function of electrode number.
|
|
|
|
|
|
|
Figure 4. Mean most comfortable loudness
levels (M-levels) for patients who received the Clarion spiral electrode and
electrode positioner (EP group) or the spiral electrode without positioner
(non-EP group) as a function of electrode number. Error bars indicate 1 SD.
|
|
|
EABR THRESHOLDS
Mean EABR thresholds for the EP and non-EP groups were not significantly
different at any electrode location (apical, middle, or basal) (Figure 5). The combined data for EP and non-EP patients showed a
main effect of electrode location (F = 3.34; P<.05),
with the mean threshold for the basal electrode being higher than the mean
threshold for the apical electrode (P<.05). Thresholds
for the apical and middle electrodes and for the middle and basal electrodes
were not statistically different.
|
|
|
|
Figure 5. Mean electric auditory brainstem
response (EABR) thresholds for patients who received the Clarion spiral electrode
and electrode positioner (EP group) or the spiral electrode without positioner
(non-EP group) as a function of electrode location. Error bars indicate 1
SD. Note that non-EP data represent only 4 patients.
|
|
|
In EP patients, mean EABR thresholds fell approximately halfway between
3-month T-levels and M-levels (Figure 6).
This indicates that, on average, current levels associated with EABR thresholds
would produce audible but not overly loud sound sensations when presented
at the pulse rate (approximately 800 pps used by the continuous interleaved
sampler speech-processing strategy. For individual EP patients, the relationship
among T-levels, M-levels, and EABR thresholds was variable. Electric auditory
brainstem response thresholds were between 3-month T-levels and M-levels for
21 electrodes tested in 8 patients but exceeded M-levels for 9 electrodes
in 4 patients.
|
|
|
|
Figure 6. Comparison of mean electric auditory
brainstem response (EABR) thresholds and mean psychophysical thresholds (T-levels)
and most comfortable loudness levels (M-levels) for 10 patients who received
the Clarion spiral electrode and electrode positioner as a function of electrode
location. Mean psychophysical data are based on the same electrodes as mean
EABR data. Error bars indicate 1 SD.
|
|
|
The 4 non-EP patients for whom EABR data were available demonstrated
a similar relationship between psychophysical measures (T-levels and M-levels)
and EABR thresholds as that described for EP patients (Figure 7). For non-EP patients, EABR thresholds fell between 3-month
T-levels and M-levels for 11 electrodes in 4 patients but exceeded M-levels
for 2 electrodes in 2 patients.
|
|
|
|
Figure 7. Comparison of mean electric auditory
brainstem response (EABR) thresholds and mean psychophysical thresholds (T-levels)
and most comfortable loudness levels (M-levels) for 4 patients who received
the Clarion spiral electrode without positioner as a function of electrode
location. Mean psychophysical data are based on the same electrodes as mean
EABR data. Error bars indicate 1 SD.
|
|
|
COMMENT
Psychophysical thresholds reported herein for EP and non-EP patients
are similar to those reported by Osberger et al1
in a larger study of adult patients. Similar to the present findings, Osberger
et al1 showed that mean T-levels were 30 to
60 CU lower in EP patients compared with non-EP patients. However, unlike
the present study, they found that threshold reductions were largest for basal
electrodes (electrodes 7 and 8). A second study of positioner effects in adults
by Lesinski-Schiedat et al2 reported no change
in mean T-levels with the positioner and showed low mean thresholds (approximately
50 CU) in EP as well as non-EP patients. In agreement with the present findings,
both studies reported lower M-levels for EP patients than for non-EP patients.
In general, results of these adult studies and the present study in children
suggest that use of the electrode positioner lowers electrical operating ranges
and reduces interpatient variability in T-levels and M-levels.
Lesinski-Schiedat et al2 also evaluated
EABR thresholds on electrode 4 in their adult patients. They found significantly
lower EABR thresholds for EP patients compared with non-EP patients, although
T-levels were not significantly different for the 2 groups in their study.
We did not observe a similar difference in EABR thresholds at any electrode
location; however, EABR data were available for only a small number of non-EP
patients in our series.
The variable relationship between T-levels and EABR thresholds observed
in this study has been reported in several previous studies primarily involving
adults.4-8
It is well established that EABR thresholds do not accurately predict T-levels,
although the 2 measures are strongly correlated. Differences in psychophysical
and EABR thresholds are primarily related to the use of faster stimulus presentation
rates for psychophysical programming of the implant speech processor compared
with the slower rates required for EABR testing.6, 8
Differences between psychophysical and EABR thresholds vary across patients
because of individual differences in temporal integration, and this precludes
use of a simple correction factor to align EABR thresholds and T-levels. The
present data show that T-levels and M-levels are relatively invariant when
an electrode positioner is used with the Clarion spiral electrode and suggest
that initial programming of the speech processor could use a common stimulus
level in most EP patients. In this case, intraoperative EABR recordings might
not be needed for purposes of T-level estimation but would still be useful
for confirming an auditory response to electrical stimulation and for evaluating
electrode placement in patients with aberrant cochlear anatomy.
A limitation of the present study was that our ability to assess the
effect of using an electrode positioner on EABR thresholds was restricted
by the variability of EABR measures within patient groups and by the small
number of non-EP patients for whom EABR data were available. This effect could
have been better studied by comparing EABR thresholds obtained intraoperatively
before and after placement of the electrode positioner in EP patients. Such
a within-patient comparison would have allowed each patient to serve as his
or her own control, thereby reducing or eliminating the problem of interpatient
variability.
CONCLUSIONS
Use of the electrode positioner decreases T-levels and M-levels in pediatric
patients with cochlear implants and substantially reduces the variablity of
such measures across patients.
It is unclear whether EABR thresholds measured at the time of implant
surgery are reduced through use of the electrode positioner. Such a result
was not observed in this study; however, EABR data were limited to only 4
patients in the non-EP group.
Use of the electrode positioner does not seem to consistently alter
the relationship between EABR thresholds and psychophysical operating range
(T-levels and M-levels). On average, EABR thresholds fall between T-levels
and M-levels; however, the relationship between EABR thresholds and T-levels
and M-levels varies considerably across individual patients.
AUTHOR INFORMATION
Accepted for publication February 6, 2001.
This work was supported in part by the 5M Lions International Hearing
Foundation, Minneapolis, Minn.
Preliminary results were presented at the 15th Annual Meeting of the
American Society of Pediatric Otolaryngologists, Orlando, Fla, May 18, 2000.
We thank 2 anonymous reviewers for helpful comments on an earlier version
of the manuscript.
Corresponding author and reprints: Gail S. Donaldson, PhD, Box 396
UMHC, 8-323 PWB, 516 Delaware St SE, Minneapolis, MN 55455 (e-mail: donal005{at}tc.umn.edu).
From the Department of Otolaryngology, University of Minnesota School
of Medicine, Minneapolis.
REFERENCES
| |
1. Osberger MJ, Koch D, Fisher L, Zimmerman-Phillips S. Clinical results in patients implanted with the Clarion® Electrode
Positioning SystemTM. Poster presented at: 1999 Conference on Implantable Auditory Prostheses;
August 30, 1999; Pacific Grove, Calif.
2. Lesinski-Schiedat A, Goldring JE, Gupta S, Battmer R-D, Frohme C, Weber BP. Evaluation of the Clarion® Electrode Positioning SystemTM
with the preformed and HiFocusTM electrode. Poster presented at: CI 2000: The Sixth International Cochlear Implant
Conference; February 3-5, 2000; Miami Beach, Fla.
3. O'Connor AF, Psillas G, Markoff L, Nunn T, McKinney C, Archer K. The effect of an electrode positioning system on cochlear implant patients. Poster presented at: CI 2000: The Sixth International Cochlear Implant
Conference; February 3-5, 2000; Miami Beach, Fla.
4. Shallop JK, VanDyke L, Goin DW, Mischke RE. Prediction of behavioral threshold and comfort values for Nucleus 22-channel
implant patients from electrical auditory brain stem response test results. Ann Otol Rhinol Laryngol. 1991;100:896-898.
PUBMED
5. Brown CJ, Abbas PJ, Fryauf-Bertschy H, Kelsay D, Gantz BJ. Intraoperative and postoperative electrically evoked auditory brain
stem responses in Nucleus cochlear implant users: implications for the fitting
process. Ear Hear. 1994;15:168-176.
PUBMED
6. Brown CJ, Hughes ML, Lopes SM, Abbas PJ. Relationship between EABR thresholds and levels used to program the
Clarion® speech processor. Ann Otol Rhinol Laryngol. 1999;108:50-57.
7. Firszt JB, Rotz LE, Chambers RD, Novak MA. Electrically evoked potentials recorded in adult and pediatric Clarion®
implant users. Ann Otol Rhinol Laryngol. 1999;108:58-63.
8. Zimmerling MS, Hochmair ES. EAP recordings in Inneraid patients: correlations with psychophysical
measures and possible implications for patient fitting. Poster presented at: CI 2000: The Sixth International Cochlear Implant
Conference; February 3-5, 2000; Miami Beach, Fla.
RELATED ARTICLE
Archives of Otolaryngology–Head & Neck Surgery Reader's Choice: Continuing Medical Education
Arch Otolaryngol Head Neck Surg. 2001;127(8):1011-1012.
FULL TEXT
|
