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Programming characteristics of cochlear implants in children: effects of
etiology and age at implantation
Paola V Incerti1, 2, 3, Teresa YC Ching1, 2, Sanna Hou1, 2, Patricia Van Buynder1, 2, Christopher
Flynn1 , and Robert Cowan2,3
Affiliations:
1.
National Acoustic Laboratories, Australian Hearing, Australia
2.
The Hearing CRC, Melbourne, Australia
3.
The University of Melbourne, Australia
Key words: children, cochlear implants, programming, etiology, age at implantation
Address for correspondence:
Paola Incerti, MAud, MAudA (CCP)
National Acoustic Laboratories
Level 5, Australian Hearing Hub
16 University Avenue
Macquarie University, NSW 2109
Australia
Email: Paola.Incerti@nal.gov.au
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Abbreviations:
ADRO: Adaptive dynamic range optimization
ACE: Advanced combination encoder
AH: Australian Hearing
ASC: Auto-sensitivity
CI: Cochlear implant
CG: Common Ground
C-level: Comfort level
CU: Clinical units
DR: Dynamic range
HA: Hearing aid
LOCHI: Longitudinal Outcomes of Children with Hearing Impairment
µA: Microamps
µs: Microseconds
MP: Monopolar stimulation
nC: Nanocoulombs
PPS: Pulses per second
SD: Standard deviation
SPEAK: Spectral Peak processing strategy
T-level: Threshold level
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Abstract
Objective: We investigated effects of etiology and age at implantation on changes in
threshold (T) levels, comfortable (C) levels and dynamic range (DR) for cochlear implants
(CIs) in children over the first five years of life
Design: Information was collected at 6-months post-activation of CIs, and at 3 and 5 years of
age.
Study sample: 161 children participating in the Longitudinal Outcomes of Children with
Hearing Impairment (LOCHI) study.
Results: Children with neural and structural cochlear lesions had higher T-levels and C-levels
as compared to those without these conditions. Parameter settings varied from manufacturer’s
defaults more often in the former than in the latter group. Investigation of the effect of age at
implantation for children without neural and structural cochlear lesions showed that those
implanted at ≤12months of age had higher T-levels and narrower DR at 6-months postactivation, as compared to the later-implanted group. For both early- and later-implanted
groups, the C-levels at 6-months post-activation were lower than those at age 3 and 5 years.
There were no significant differences in T-levels, C-levels, or DR between age 3 and 5 years.
Conclusions: Etiology and age at implantation had significant effects on T-levels and Clevels.
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Introduction
The goal of the cochlear implant (CI) programming procedure is to maximise the speech
information available to the user. This is particularly important in infants and young children
who are using input from their CI to develop speech and language. An important aspect of
programming a CI for any individual is the process of determining appropriate electrical
current levels for each electrode to provide the user with a dynamic range from just audible to
maximum comfortable hearing sensations (Shapiro and Bradham, 2012). This process, also
known as ‘Mapping’, utilises manufacturer’s proprietary software and a hardware interface to
program the sound processor. The clinician has access to a range of settings for various
electrical parameters through the programming software, enabling customisation of the
program to suit the individual’s need (Wolfe and Schafer, 2015).
During the Mapping process, several decisions need to be made including: choice of sound
coding strategy; stimulation rate; stimulation mode; number of electrodes used (channels); as
well as CI device parameters specific to the implant system chosen. CI manufacturers provide
default recommendations for setting of these parameters in their proprietary programming
software (Boyd, 2010; Vaerenberg, et al., 2014). Other parameters, such as setting the
hearing threshold (T) and maximum comfortable (C) current levels for each electrode need to
be measured for each individual CI recipient using behavioural and/or objective measures
(Hodges et al., 1997; Brown, 2003; Gordon et al., 2004). The difference between T- and Clevels is termed the dynamic range (DR). The range of values selected for the CI parameters
by the clinician control the conversion of acoustic signals into electrical stimulation and is
referred to as the ‘MAP’ or listening program. Initial device activation generally occurs 2-6
weeks after surgery. In general, a CI recipient attends about six appointments in the first year
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after implantation until the values set for specific CI parameters such as current levels are
stable; subsequently the MAPs are reviewed annually (Shapiro and Bradham, 2012; Uhler
and Gifford, 2014; Vaerenberg et al., 2014). The fitting of an individualised, usable, accurate
program is a critical part of the postoperative rehabilitation management program and can
significantly influence CI recipient outcomes (Baudhuin et al., 2012; Boyd et al., 2010; Boyle
and Moore, 2015; Sainz et al., 2003; Wasowski et al., 2010; Zhou and Pfingst, 2014).
A global survey of CI programming practices across 47 CI centres reported that the most
common fitting practice during initial or follow-up CI programming sessions was the check
of individual electrode function by measuring their electrical impedances. The second most
common practice reported was the setting of T- and C-levels on each electrode to be included
in the MAP (Vaerenberg et al., 2014). The authors reported that ‘Most, if not all, centres’
focus goes to the setting of threshold and the maximum comfortable current levels, to ensure
that soft sounds are audible and loud sounds are comfortable and that loudness is balanced
across the electrode array’. In adults and older children, T- and C-levels can typically be
measured using standard psychophysical behavioural responses to electrical stimuli. In
younger children, however, the setting of these levels are more challenging and time
consuming (Hughes et al., 2001; Morita et al., 2004). The use of age-appropriate techniques
such as behavioural observation audiometry (BOA), visual reinforcement audiometry (VRA)
or conditioned play audiometry are utilised to determine these levels (Zowlan, 2009). In cases
where only a few behavioural measurements can be made, interpolation of levels on
unmeasured electrodes located between measured electrodes, and the setting of fixed DR
across all electrodes or global adjustments of levels may be necessary to create a MAP
(Wolfe and Schafer, 2015). Objective measures such as electrically evoked compound action
potential (ECAP), auditory brainstem potential (EABR) and stapedius reflex (ESR) are also
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routinely used in conjunction with behavioural measures to assist with the estimation of both
T- and C-levels and can expedite the establishment of a MAP (Gordon et al., 2004). In infants
and very young children for whom conditioned behavioural responses are not possible,
electrophysiological responses have a dominant role in guiding clinicians in the fitting and
setting of T- and C-levels (Zowlan, et al., 2008). In the initial stages of paediatric
programming, when limited information is available, clinicians in general take a conservative
approach to setting ranges of stimulation, in particular for C-levels (Wolfe and Schafer, 2014;
Zowlan et al., 2008). Compared to adults, setting of current levels in children has been
reported to take longer to stabilize (Hughes, et al., 2001).
Several studies have investigated changes in T- and C-levels that may occur over time to
provide information that may assist with post-operative programming of parameters,
management procedures and service provision. Previous paediatric studies have reported that
mean T-levels stabilize within the first 3 months to 1 year post-activation and that C-levels
stabilize within the first 6 months to 2 years post-activation (Henkin et al., 2006; Hughes et
al., 2001; Van Den Abbeele et al., 2012; Vargas et al., 2013; Zwolan et al., 2008). Several
studies investigating the setting of T- and C-levels for straight versus perimodiolar electrodes
have reported significantly lower mean T- and C-levels for perimodiolar arrays designed with
closer placement to the modiolus (Frank et al., 2002, Gordon et al., 2013; Jeong et al., 2015;
Telmesani et al., 2015). Current levels have also been reported to vary along the length of the
cochlea, with higher mean T- and C-levels recorded in the basal region as compared with
medial and/or apical regions (Gordon et al., 2004; Henkin et al., 2003; Raghunandhan et al.,
2014; Vargus et al., 2013). Several studies have suggested that these higher mean T- and Clevels in the basal region may be due to the presence of fibrotic tissue or to lesser integrity of
the auditory nerve fibres in this region (Henkin et al., 2003; Mosca et al., 2014).
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A number of studies have investigated whether etiology may have an effect on T- and Clevels. Compared to patients who do not have cochleovestibular anomalies, higher T- and Clevels have been anecdotally reported in case studies describing series of patients with
common cavity, Mondini, cochlear hypoplasia, or enlarged vestibular aqueduct (Coelho and
Roland, 2012; Eisenman et al., 2001; Woolley et al., 1998); or hypoplastic cochlear nerve and
narrow internal auditory canal (Bradley, 2008; Lee et al., 2012; Valero et al., 2012); or
cochlear osteogenesis due to meningitis (Durisin et al., 2014; Eshraghi et al., 2004). Vargas et
al. (2013) reported significantly higher mean T- and C-levels in a group of patients with
meningitis and cochleovestibular anomalies compared to a group of patients with normal
cochleovestibular anatomy. Requirements for higher current levels have been largely
attributed to atypical electrode positions and/or target neural cells (Coelho and Roland, 2012;
Turrini et al., 1997). A range of accompanying programming issues such as non-auditory
stimulation (pain or facial nerve stimulation), inability to obtain an auditory response, and
failure to achieve appropriate loudness growth due to electrode compliance issues have been
described. Studies have also reported narrowing of DRs due to the setting of low C-levels to
eliminate non-auditory stimulation and pain (Lee et al., 2012; Papsin, 2005). Papsin (2005)
reported a statistically significant reduction in DR and increased incidence of facial nerve
stimulation in children with common cavity deformity and hypoplastic cochlea as compared
to children with normal cochleovestibular anatomy. Most of these studies are retrospective,
and include subjects with a wide range of ages at implantation (mean age ranging from 2.9 to
5.8 years). To date, there is limited information on changes in T- and C-levels over time for
specific etiological groups in young paediatric cohorts.
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Age at implantation has also been reported to affect the setting of T-and C-levels in a few
studies. Gordon et al. (2004) reported significantly higher T-levels in a group of 28 infants
and toddlers implanted under 3 years of age (0.7- 2.9 years) as compared to a group of 24
preschool children (3 to 5.9 years) and 16 school-aged children (6 -17 years) using Nucleus
CI 24M, CI24R and CI24RE devices (Cochlear Ltd, Sydney, Australia). Behavioural
measures for three stimulating electrodes located in basal, medial and apical cochlear
segments were obtained using standard, age-appropriate audiometric procedures. There was
no significant effect of age at implantation on C-levels or objective measures (ECAP, EABR
and ESR) obtained at 2 days after implantation, 1, 3, 6 and 12 months after CI activation.
Gordon et al. (2013) reported data from 182 children implanted between 0.7 and 17 years
(mean: 6.61, SD: 5.13) showing similar findings as their earlier study It should be noted that
while the earlier study included children with cochlear abnormalities, the latter study
excluded children with cochlear abnormalities or with partial CI electrode array insertions.
The higher T-levels recorded in infants and toddlers as compared to the other groups were
largely attributed by Gordon and colleagues to the BOA method used for programming,
which was more likely to overestimate levels compared to methods that used conditioned
responses. Gordon et al. (2013) also suggested that the finding of higher T-levels in preschoolers (3 to 5.9 years) as compared to school-aged children (6 -17 years) might be due to
immaturities in central auditory areas or in cognitive and attentional centres.
In contrast, Vargas et al. (2013) showed that T-levels in younger children using the Combi
40+ devices (Med-El, Innsbruck, Austria) were significantly lower than those in older
children and adults. They reported data on 121 CI users. Patients with a minimum of 6
month’s listening experience with their devices were grouped into three age categories: those
implanted between 18 months and 5 years of age; between 5 and 16 years; and between 16
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and 63 years. Patients with cochlear abnormalities were excluded. Mean T- and C-levels for
the entire electrode array were obtained from MAPs collected at least 6 months after the
initial activation. As for the Gordon et al studies, C-levels were not significantly influenced
by the age at implantation. The conflicting T-level findings may be related to the clinical
methods of programming or to the characteristics of the different cochlear implant systems.
Changes in clinical practice are leading to significant numbers of children receiving a CI
under 12 months of age. Currently there is limited information regarding the setting of T- and
C-levels in these children compared to those who received a CI after 12 months of age.
The worldwide survey of CI programming practices by Vaerenberg, et al. (2014) suggested
that, apart from setting of T- and C-levels, fitting parameters were rarely modified from the
default setting in majority of CI recipients. For Nucleus devices, about 6-15% of fittings had
modifications to the number of active electrodes; stimulation rate (number of biphasic
electrical pulses delivered to an electrode contact per second or pps); number of maxima
(largest bandpass filter outputs); and pulse width (duration of each phase of a biphasic
electrical phase). The criteria used to identify those CI recipients that may require
modifications made to their MAP parameters varied across centres, including the CI
recipient’s subjective feedback (Vaerenberg et al., 2014) and the presence of cochlear
abnormalities (Boyd, 2010). It has been reported that children with
cochleovestibular anomalies and hypoplastic cochlear nerve and/or narrow internal auditory
canal have wider pulse widths, fewer active electrodes, and slower stimulation rates than
others without those abnormalities (Bradley et al., 2008; Dettman et al., 2011; Eisenman et
al., 2001; Papsin, 2005). Case studies of these MAP issues have reported ‘difficult’,
‘challenging’ and/or ‘frequent’ programming sessions (Bradley et al., 2008; Coelho and
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Roland, 2012; Lee et al., 2012; Papsin, 2005; Tucci et al., 1995; Vargus et al., 2013; Woolley
et al., 1998;), or suboptimal MAPs (Bradley et al., 2008; Coelho and Roland, 2012; Papsin,
2005; Valero et al., 2012). A number of studies have described the MAP parameter changes
in specific etiological groups, however so far, changes in MAP parameters from default
setting over time for specific etiological groups in young paediatric cohorts has received
limited attention.
Extension of CI candidacy criteria to include infants and those with more complex
anatomical cases and additional disabilities has resulted in new programming challenges
(Sampio et al., 2011). To date, there is little information on how programming parameters
selected relate to etiology or age at implantation in large cohorts of young children. The
Longitudinal Outcomes of Children with Hearing Impairment (LOCHI) study provides a
unique opportunity to review the clinical CI programming parameters of a relatively large,
young paediatric population that has been followed consistently since implantation.
The LOCHI study is a prospective, population-based study that was aimed to investigate the
relationship between age at intervention and speech, language, functional and psychosocial
outcomes of children with hearing loss in Australia (Ching et al., 2013). The participants are
a cohort of about 450 children born between 2002 and 2007 in three states of Australia (New
South Wales, Victoria and Queensland) who were fitted with hearing aids by Australian
Hearing (AH) before three years of age (Ching et al., 2013). The children’s outcomes were
assessed using a combination of standardized tests and validated measures, which included
both direct, age-appropriate assessments and parent reports. Evaluations occurred at 6 and 12
months after initial device (hearing aid or CI) fitting, and then when the children were 3 and 5
years of age. Information about demographic characteristics and audiological characteristics
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are collected at the same intervals. This paper draws on CI parameters collected as part of the
study. The data collected at 6 months after CI activation, and then at 3 and 5 years of age
were analysed to investigate the effects of etiology and age at implantation on changes in Tand C-levels and DR over time. The parameter settings of the CIs used by the cohort at 5
years of age and over time are described in relation to manufacturer default settings. This
study was conducted under the approval and oversight of the institutional human research
ethics committee.
The aims of the study were to investigate changes in T- and C-levels and DR over the first 5
years of life in children using cochlear implants. Specifically, we examined changes over
time for: 1) different etiology groups; and 2) different age at implantation groups. Our
secondary aim was to compare the programming parameters used in children’s CIs to
manufacturer default values to increase understanding about current clinical practice.
Method
Participants
The participants included children enrolled in the LOCHI study at 5 years of age, who have
received a CI before 3 years of age. All CIs are Nucleus devices (Cochlear Ltd, Sydney,
Australia).
Clinical programming practice
All children had their CI sound processors programmed at their respective Cochlear Implant
Centres, independent of this study. In general, T- and C-levels are measured using standard,
age-appropriate, audiological behavioural techniques. BOA, VRA or conditioned play
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audiometry are utilised, depending on a child’s developmental abilities. In cases where only a
few behavioural measurements can be made, interpolation of levels on unmeasured electrodes
located between measured electrodes, and the setting of fixed DR across all electrodes or
global adjustments of levels are some techniques used to create a MAP. Objective measures
such as ECAP, and EABR are also routinely used in conjunction with behavioural measures
to assist with the estimation of both T- and C-levels. In infants and very young children for
whom conditioned behavioural responses are not possible, including those with cognitive
deficits, electrophysiological responses have a dominant role in guiding clinicians in the
setting of T- and C-levels. In the initial stages of paediatric programming when limited
information is available, clinicians in general take a conservative approach to setting current
levels, in particular for C-levels.
For all other programming parameters, the CI clinics typically use the default parameter
settings recommended in the Cochlear programming software at initial device activation and
routine follow-up sessions. In general, modifications to parameter defaults are made only
when deemed necessary by clinician and based on an individual’s need. Cochlear software
has ‘HearingMentor’ to provide guidance and tips for troubleshooting and adjustment of
parameters for clinicians.
Procedure
Data collection
The children’s CI information was collected at six months after initial cochlear activation, at
3 years, and 5 years of age; according to the LOCHI study protocol. Information about the CI
device type, sound processor model and Cl MAP parameters for each of the children was
obtained at each time interval.
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Calculation of T-levels and C-levels
T-level and C-level in clinical units (CU), which are defined by the Cochlear Ltd
programming software, are determined by the delivered electric charge per phase (current
amplitude X pulse width). The delivered current amplitude (in µA) differs between the CIC3
(CI24M or CI24R) and CIC4 (CI24RE) implant types. In addition, the pulse width (µs/phase)
was not the same across children. We therefore calculated the delivered charge per phase for
T- and C-levels, and report these in dB (re: 1 nC). Using tables supplied by Cochlear Limited
(Busby, personal communication), CU were converted to current amplitude (µA), and then
multiplied by pulse width to calculate charge-per-phase. The relationship between current CU
and charge dB is linear. Table1 gives an example of the calculations used for both a CIC3 and
CIC4 implant type with pulse widths of 25 µs and clinical units of 200 CU.
<Table 1 about here>
Calculation of mean T- and C-levels for basal, medial, and apical segments
T- and C-levels were recorded for all electrodes, and mean values for three cochlear segments
were calculated. Apical segments were defined as all active electrodes allocated to the input
frequency range of 188 Hz to 1063 Hz. Medial segments included all active electrodes
allocated to the input frequency range of 1063 Hz to 3063 Hz. Basal segments were all active
electrodes allocated to the input sound frequency range of 3063 Hz to 7938 Hz. In a Nucleus
CI with all electrodes activated (22 channels), these frequency ranges correspond to the
following electrode allocation across cochlear segments: basal (Electrode 1 or E1 to E7);
medial (E8 to E14); and apical (E15 to E22). This categorization was based on the clinical
fitting default recommendations provided in programming software (Custom Sound 4.4) for
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frequency-to-electrode allocation tables (FAT) for the Nucleus® Freedom™ and Nucleus® 6
sound processors (Cochlear Ltd). The approach adopted in the paper takes into account the
clinical scenario in programming with regard to the default software frequency-to-electrode
allocation for any number of active electrodes. As electrodes become deactivated, the
frequency bandwidth of each channel becomes wider but the overall input frequency range
remains the same (Wolfe and Schafer, 2015). The approach allowed all participants,
including those using CI systems with multiple electrodes being deactivated (e.g. those with
cochleovestibular anomalies), to all be included in the analysis.
Data analysis
Descriptive statistics and analysis of variance (ANOVA) were used to compare across groups
and time intervals. The statistical analysis was done using Statistica v.10 (Statsoft Inc., 2011)
All analyses used two-tailed tests, with statistical significance set at p <0.05.
To investigate the effect of etiology on changes of CI parameter settings over time, children
were grouped into 1) those diagnosed with auditory nerve deficiency, 2) those with cochlear
lesions (including common cavity, Mondini, cochlear hypoplasia), 3) those with large
vestibular aqueduct syndrome, 4) those with auditory neuropathy spectrum disorder, 5) those
with additional disabilities (including autism spectrum disorder, cerebral palsy,
developmental delay, disorders of vision, speech output, syndromes, medical disorders), and
6) all other children (unknown etiology, genetic factors and cytomegalovirus infection).
To investigate the effect of age at implantation on changes in CI parameter settings over time,
children were grouped according to whether they received their first CI at ≤12 months or
later. As auditory nerve deficiency, cochlear lesions and meningitis have been known to
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affect CI parameter settings (Lee et al., 2012; Papsin, 2005; Valero et al., 2012; Vargus et al.,
2013) independent of age at CI, children with these characteristics were excluded from this
analysis.
To examine the extent to which CI parameter settings in the present cohort vary from
manufacturer’s default settings, we focused on pulse width, stimulation rate, number of active
electrodes, and number of maxima; as these have been known to be modified often in
programming practice (Bradley et al., 2008; Eisenman et al., 2001; Papsin, 2005; Vaerenberg,
et al., (2014). Descriptive statistics were used for this comparison.
Results
Data from 161 children participating in the LOCHI study are reported in this paper. The
demographic characteristics are shown in Table 2. The mean age at activation of the first CI
is 22.1months (SD: 13.5; Range: 5.3 to 59.6). Ninety-three children had bilateral CIs (12
simultaneously and 81 sequentially). For sequential implantation, the mean time interval
between the first and the second CI was 16.6 months (SD:11.6, Range: 2 to 48). All children
used a Nucleus device (Cochlear Ltd). The mean and standard deviation (SD) of T- and Clevels of CIs at 5 years of age are provided in Table 3, separately for each etiology group.
Table 4 provides information about the CI type, sound processor and MAP parameters.
<Table 2, 3 and 4 about here>
Effect of etiology
The effect of etiology on changes in T-levels, C-levels and DR over time was investigated for
108 children (130 ears). Data collected at 6-months post-activation of CIs, at age 3 years and
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at 5 years were analysed. When a child had a 6 months post-activation of CI assessment
interval that overlapped with his/her 3 years of age assessment interval (1 data point), they
were excluded from this longitudinal analysis.
T-levels
Figure 1 shows the T-levels as recorded along the electrode array at three different segments
for the six etiological categories over time. As shown, T-levels for children with auditory
nerve deficiencies (Etiology group or EGp 1) were consistently higher than for other
etiological categories, and this was found across all three cochlear segments.
<Figure 1 about here>
Analyses of variance (ANOVA) using T-levels at basal, medial and apical segments as
dependent variables, time interval (6-months post-activation, age 3 years, age 5 years) as
repeated measures, and etiological category (auditory nerve deficiency, cochlear lesions,
LVAS, ANSD, AD, others) as categorical variables showed that the main effect of etiology
was significant (F[5,123] = 5.26, p < 0.001). The main effect of cochlear segment was also
significant (F[2,246] = 12.91, p < 0.001). There were no other significant main effects or
interactions. Post-hoc analyses using Bonferroni corrections revealed that on average, the
basal, medial, and apical segment charge levels of the auditory nerve deficiency group were
significantly higher as compared to those with additional disabilities (p = .009, p = 0.0007, p
= 0.01 respectively), or those in the ‘others’ category (p = 0.003, p = 0.008, p = 0.012).
C-levels
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Figure 2 shows changes in C-levels over time at different cochlear segments for 6 etiology
groups.
<Figure 2 about here>
ANOVA using C-levels at basal, medial and apical segments as dependent variables, time
interval (6-months post-activation, age 3 years, age 5 years) as repeated measures, and
etiological category (auditory nerve deficiency, cochlear lesions, LVAS, ANSD, AD, others)
as categorical variables showed that the main effect of etiology was significant (F[5,123] =
8.06, p < 0.001). The main effects of time interval (F[2, 246] = 3.35, p = 0.04) and cochlear
segment were also significant (F[2,246] = 13.31, p < 0.001). There were no other significant
interactions. Post-hoc analyses using Bonferroni corrections showed that C-levels for those
children with auditory nerve deficiency were significantly higher from those with LVAS (p =
0.02), ANSD (p = 0.014), additional disabilities (p < 0.001), or ‘others’ (p < 0.001). On
average, the group with cochlear lesions was also significantly higher from that with
additional disabilities (p = 0.002) and ‘other’ (p < 0.001). Post-hoc analyses of the effect of
time interval revealed that on average, the C-levels at 6-months post-activation were
significantly lower as compared to those at age 3 and 5 years (p <0.001), but there was no
significant difference between the C-levels at age 3 and at 5 years (p > 0.05). Post-hoc tests
of the effect of cochlear segment showed that on average, higher C-levels were recorded in
electrodes in the basal segment as compared to electrodes in the medial segment (p = 0.002),
but were not different from apical electrodes. In addition, the medial segments had
significantly higher charge level, on average, than apical segments.
DR
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The DR was calculated by taking the difference between T-levels and C-levels, expressed in
terms of dB (re: 1 nC). Figure 3 shows changes in DR over time at three cochlear segments
for 6 etiology groups. Table 5 gives the overall DR averaged across all electrodes for the 6
etiology groups across the three measurement time points, at 6-months post-activation of CIs,
at age 3 years and at 5 years.
<Figure 3 about here>
ANOVA using DR as dependent variable, etiology as categorical variable, and cochlear
segment and time interval as repeated measures showed that the main effect of cochlear
segment was significant (F[2,246] = 3.078, p = 0.047). There were no other significant main
effects. The interaction between cochlear segment and etiology was significant (F[10,246] =
1.944, p = 0.04). Post-hoc analyses revealed that for children with auditory nerve deficiency
at age 5 years, the DR for electrodes in the basal segment was significantly lower as
compared to DR on electrodes in the apical segment (p = 0.012). There were no other
significant effects.
Effect of age at implantation
Data from 88 children who provided information at all 3 time intervals (n =98 ears) were
analysed to investigate the effect of age at implantation on changes in T-levels, C-levels, and
DR over time. As indicated in the Methods section, we excluded, a priori, data from children
with auditory nerve deficiency (n=7 ears), cochlear lesions (n =10 ears), meningitis (n=3
ears) and recurrent mastoiditis (n=1) from this analysis. Of the 98 ears, 43 ears had an
implant activated at or before 12 months of age (early-implanted), and 55 ears had an implant
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activated after 12 months of age (later-implanted). At 3 years of age, the early implanted
group had a mean duration of CI experience for 28.2 months (SD: 2.4; Range: 24.0 to 34.1),
and the later implanted group had a mean duration of CI experience for 18.7 months (SD: 5.3;
Range: 7.6 to 28.5 months).
T-levels
Figure 4 shows the mean T-levels at three time intervals for the two age at implant groups of
children.
<Figure 4 about here>
ANOVA using T-levels as dependent variable, age at implantation as a categorical variable
(early vs later), time interval (6-months post-activation, age 3 years, age 5 years) and
cochlear segment (basal, medial, apical) as repeated measures revealed that the main effect of
age at implantation was significant (F[1,96] = 5.65, p = 0.02). The interaction between time
interval and age at implantation was significant (F[2,192] = 7.59, p <0.001). Post-hoc
analyses revealed that T-levels were significantly higher for the early-implanted group as
compared to the later-implanted group at 6-months post-activation, but not at 3 or 5 years of
age. There were no other significant main effects or interaction.
C-levels
Figure 5 shows the mean C-levels for the two age at implantation groups of children across
the three time intervals (6-months post-activation, age 3 years and age 5 years).
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<Figure 5 about here>
ANOVA using C-levels as dependent variable, age at implant as categorical variable, and
cochlear segment and time interval as repeated measures showed significant main effects of
age at implant (F[1,96] = 4.25, p = 0.04), time interval (F[2,192] = 5.59, p = 0.004), and
cochlear segment (F[2,192] = 23.15, p <0.001). There were no significant interactions. On
average, the C-levels at 6-months post-activation of CIs were significantly lower than those
recorded at age 3 or 5 years, whereas there was no significant difference in mean C-levels
recorded for age 3 and age 5 years. Across both age at implantation groups, electrodes in the
basal segment of the cochlea had lower C-levels than those located in medial and apical
segments.
DR
Figure 6 shows the mean overall DR (averaged across all electrodes) for the children grouped
according to their age at implantation across the three measurement time intervals.
<Figure 6 about here>
ANOVA using DR as dependent variable, age at implantation as categorical variable,
cochlear segment, and time interval as repeated measures showed that the main effect of time
interval was significant (F[2,192] = 3.47, p = 0.03). In addition, the main effect of cochlear
segment was significant (F[2,192] = 4.06, p = 0.02). There was significant interaction
between time interval and age at implantation (F[2,192] = 3.05, p = 0.049). Post-hoc tests
revealed that the DR at 6-months post-activation for the early-implanted group was
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significantly narrower (6.4 dB [SD 2.1]) as compared to the later-implanted group (mean 7.1
dB [SD 1.8]). There were no other significant interactions. Across both groups, DRs recorded
for electrodes in the basal segment of the cochlea were narrower as compared to electrodes in
the medial segments.
Parameter settings: Default versus non default
The secondary aim of this study was to compare the settings for pulse width, stimulation rate,
number of active electrodes and number of maxima used in children’s devices with the
manufacturer’s default settings. The comparison was made for each of the 6 etiology groups.
In addition, the proportion of default vs non-default values for each of the 4 parameters were
examined for the early and later-implanted groups. Whilst the majority of CI fitting
parameters were rarely modified from the manufacturer’s software recommended default
setting for 5 years, a small proportion of children did have modifications made to their MAPs
(see Table 4).
Proportion of non-default settings for 6 etiology groups
Figure 7 shows the percentage (%) of MAPs that have non-default settings for pulse width,
stimulation rate, number of active electrodes, and number of maxima.
<Figure 7 about here>
As shown in Figure 7, children with auditory nerve deficiency showed the highest percentage
of non-default settings for pulse width (100%) and stimulation rate (range: 43-86%) at all
three time intervals. The group of children with cochlear lesions showed the highest
percentage of deactivated electrodes (range: 60-70%), followed by the group of children with
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auditory nerve deficiency (range: 43-57%) over time. The percentage of non-default
parameter settings also increased over time for stimulation rate and number of active
electrodes for both of these groups. There were also considerable variations in the number of
maxima from default recommendations, generally in the direction of an increase in the
number of maxima.
Proportion of non-default settings for early vs later implanted groups
Figure 8 shows the percentage (%) of MAPs set to the non-default settings for pulse width,
stimulation rate, number of active electrodes, and number of maxima.
<Figure 8 about here>
For pulse width, stimulation rate, and number of electrodes used, the proportion of nondefault parameter settings are similar between the early- and later-implanted groups.
However, the proportion of non-default settings for the number of maxima appeared to be
higher for the early-implanted than for the later-implanted group.
Discussion
This study reported on the CI programming parameters of 161 children who were using CIs
by 3 years of age in the LOCHI study (Ching et al., 2013). We investigated changes in Tlevels, C-levels, and DR from 6 months post-activation of CI to 5 years of age. The effects of
etiology and age at implantation on these changes were reported. In addition, the proportion
of MAPs that used settings for pulse width, stimulation rate, number of active electrodes, and
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number of maxima that varied from the manufacturer’s default settings was described to
increase understanding about current clinical practice.
Effect of etiology on T-levels, C-levels, and DR
Averaged across three measurement time intervals of 6-months post-activation, age 3 years
and age 5 years, T-levels and C-levels for children with auditory nerve deficiency were found
to be set significantly higher than for the group of children with additional disabilities or for
those children in the ‘other’ category (comprising children with unknown, genetic factors and
CMV). Mean C-levels for 7 children with auditory nerve deficiency were significantly higher
than all other etiological categories except those children with cochlear lesions. Consistent
with previous studies that reported that high C-levels for children with cochlear lesions
(Vargus et al., 2013; Wooley, et al., 1998), mean C-levels for the cochlear lesions etiological
category were significantly higher than those children with additional disabilities or those in
the ‘other’ etiological category (comprising children with unknown, genetic factors,
congenital cytomegalovirus (CMV) infection). These findings suggest that when clinicians
are programming MAPs for children with auditory nerve deficiency or cochlear lesions, they
should be aware that higher T-levels or C-levels might be required as compared to MAPs for
children without those conditions. As shown in Figs 1 to 3, there is considerable individual
variability (as depicted by the 95% confidence intervals) in children with auditory nerve
deficiency, cochlear lesions, and LVAS, compared to children without these conditions.
When creating a MAP for children with auditory nerve deficiency or etiologies involving
cochlear lesions or LVAS, clinicians might choose a programming approach that is less
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reliant on interpolation of levels, fixed DR or global adjustment techniques as compared to
approaches used for children without those conditions.
This study extends previous retrospective studies on CI parameters of children by tracking
changes in CI parameters set at 6-months post-activation to age 3 years and then 5 years in a
population-based cohort; showing that on average, there were no significant changes in DR
across the specified time period (duration of CI use ranged from 31 months to 55 months,
median: 46.4 months). It appears that the DR has stabilised by the measurement point at 3
years of age (mean duration of CI experience was 25.1 months, SD: 9.7; Range: 7.6 to 52.0).
It may be expected that by 3 years old, reliable behavioural responses to electrical stimulation
may be obtained for most children to facilitate optimal setting of CI parameters.
Averaged across all etiology groups, mean C-levels were significantly lower at 6-months
post-activation of CI, compared to C-levels at age 3 and 5 years. This is likely due to clinical
programming practice of remapping to increase C-levels over time. There was no significant
difference in C-levels between 3 and 5 years of age, suggesting that the C-levels remained
stable over this time. To the authors’ knowledge, no study has examined changes in C-levels
beyond 2 years after implantation. The main effects of cochlear segment and higher mean Tand C-levels found in the basal segment as compared with medial and/or apical regions were
also consistent with previous findings (Gordon et al., 2004; Henkin et al., 2003;
Raghunandhan et al., 2014; Vargus et al., 2013).
Effect of age at implantation on T-level, C-level and DR
For children who received a CI before 12 months of age, there was a consistent reduction in
recorded T-levels and an increase in C-levels between the 6-months post-activation time
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period and 3 years of age. This was not observed in the later-implanted group of children.
Consequently, the DR at 6-months post-activation was significantly narrower than that at 3
years of age for the early-implanted group, but not for the later-implanted group. This
necessarily resulted in a narrower DR observed for the early-implanted group as compared to
the later-implanted group, at 6-months post-activation. However, there were no significant
difference in T-levels or C-levels or DR between 3 and 5 years of age, both for the early- and
the later-implanted groups. The setting of higher T-levels for the early-implanted group as
recorded at the first two measurement time intervals may be related to the greater reliance on
BOA that overestimates threshold levels in clinical practice (Gordon et al., 2013), or the
adoption of a conservative programming bias in practice for young children (Wolfe and
Schafer, 2015), or some combination of these factors. On the other hand, programming of CI
for older children can utilise standard audiometric procedures to provide a reliable estimate of
T-levels. Nevertheless, the individual variability of the early-implanted group was similar to
that in the later-implanted group (Figs 4-6). The DR at 6 months post-activation of CI was
similar to that at 3 years and 5 years for the later-implanted group, but narrower than that at 3
and 5 years for the early-implanted group. This suggests that the DR took longer to be
optimised for children receiving their CI before 12 months of age (despite their longer
duration of using CIs by 3 years of age) as compared to those who were implanted after 12
months of age. A less conservative approach to setting T-and C-levels might be considered in
early-implanted children than that adopted in current practice.
Future studies will investigate the factors influencing the programming practices of clinicians
working with children who received CIs before 12 months of age in the present cohort. This
is an important clinical question as current evidence from the LOCHI study clearly supports
cochlear implantation for children before 12 months of age to facilitate early language
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development (Ching et al., 2017). A greater awareness of how programming parameters
change over time in infants and young children is critical to ensure that CI parameters are
optimised as early as possible to maximise outcomes from early implantation.
Proportion of non-default settings in pulse width, stimulation rate, number of active
electrodes and number of maxima
For children with either auditory nerve deficiency or cochlear lesions, clinicians’ settings of
pulse width, stimulation rate and number of active electrodes were more likely to deviate
from the manufacturer’s recommended default settings than for other children. These findings
are consistent with previous retrospective studies that have reported on common
modifications made on MAPs for children with cochleovestibular anomalies (Coelho and
Roland 2012; Dettman et al., 2011; Papsin, 2005; Vargas et al., 2013; Woolley et al., 1998),
and/or hypoplastic cochlear nerve and narrow internal auditory canal (Bradley, 2008; Lee et
al., 2012; Valero et al., 2012). The present data suggest that CI programming for children
with auditory nerve deficiency might benefit from an initial setting of pulse width to be wider
than the default setting. Typically, they also require slower stimulation rate than default
settings (see Table 4 for default settings). However, a limitation to generalisation from the
current study is the small number of children with auditory nerve deficiency.
The findings from this study underscore the importance of investigating the CI programming
parameters for different etiological categories in children. We found no significant
differences in programming parameters set for children with LVAS, ANSD, additional
disabilities, or ‘other’ (unknown, genetic factors and CMV); however, those with neural or
structural lesions may require special attention to the setting of MAP parameters such at Tlevels and C-levels to ensure optimisation at the earliest possible time. Further, the present
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study found that children who received a CI before 12 months of age did not achieve optimal
settings in T-levels and C-levels at 6 months after implantation, whereas children who
received an implant after 12 months of age achieved optimal settings by 6 months after
activation. This suggests that an increased understanding of factors influencing CI
programming practices for infants who receive CIs early may assist clinicians to optimise
parameter settings earlier than is current practice to maximise the benefit of early
implantation.
Conclusion
This study evaluated the programming parameter characteristics of children participating in
the LOCHI study who were using CIs by 3 years of age. Children who have neural or
structural lesions were found to have different programming requirements from those without
these conditions. On average, CI parameters were stable by 3 years of age, and no significant
changes were observed 3 year and 5-year time intervals. Further, optimal settings were
achieved by 6-months post activation for those children who received a CI after 12 months of
age, but took longer for those who received a CI at a younger age. Improved clinical practice
should be directed towards achieving optimal settings for infants who received a CI before 12
months of age so as to capture the benefit of early implantation.
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Acknowledgements and Declaration of Interest
Sources of funding
The project was supported by the Commonwealth of Australia through the Office of Hearing
Services and through the HEARing CRC, established and supported under the Cooperative
Research Centres Program of the Australian Government. We also acknowledge the support
provided by New South Wales Department of Health, Australia; Phonak Ltd; and the Oticon
Foundation.
This work was also partly supported by the National Institute on Deafness and Other
Communication Disorders (Award Number R01DC008080). The content is solely the
responsibility of the authors and does not necessarily represent the official views of the
National Institute on Deafness and Other Communication Disorders or the National Institutes
of Health.
Acknowledgements
The authors would like to thank all the children and their families for participation in this
study. We are also indebted to the many persons who served as clinicians for the study
participants or assisted in other clinical or administrative capacities at Australian
Hearing, Hear and Say Centre, Mater Hospital Brisbane, Royal Institute for Deaf and Blind,
The Melbourne Cochlear Implant Centre, Royal Children’s Hospital Foundation, Royal
Institute for Deaf and Blind Children, Royal Victorian Eye and Ear Hospital, and The
Shepherd Centre.
We gratefully thank Peter Busby (Cochlear Ltd.) for his advice and assistance with
calculation of current levels of stimulation in cochlear implants. We also thank Vicky Zhang
(NAL) for her assistance with preparation of the manuscript.
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Conflict of Interests
The author(s) declared no potential conflicts of interest with respect to the authorship and/or
publication of this article.
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