Long-term electrode impedance changes and failure prevalence in cochlear implants

<div><p></p><p><i>Objective:</i> This study assessed the prevalence of electrode failures and electrode impedance measures in Nucleus cochlear implants around initial activation (an average of 16 days after surgery) and after 8 to 12 years of device use. <i>Design:</i> Retrospective data from the Melbourne Cochlear Implant Clinic was collated and analysed. <i>Study sample:</i> Included in this study were 232 adults, all of whom were implanted at the clinic between March 1998 and August 2005. <i>Results:</i> Overall 0.5% of electrodes failed over the entire test period, with 5.6% of devices showing one or more electrode failure. The majority of these failures were recorded by initial activation. The numbers of electrode failures have decreased over time with array type, such that no failures were recorded with the currently available Contour Advance array. Array type was shown to affect electrode impedance at both time points, with the Contour and Contour Advance arrays having significantly higher absolute values than the Banded array. However, the Banded array had significantly higher area-normalized impedances at initial and final measures than the Contour and Contour Advance array. <i>Conclusions:</i> A relatively low incidence of electrode failures were recorded for the Nucleus devices of these recipients. Electrode impedance dropped for all array types after 8 to 12 years of device use.</p></div

Absolute numbers of the various etiologies defined in the dataset.

<p>These etiologies are classified by poorest to best speech outcome in quiet with a CI. ANSD: Auditory neuropathy spectrum disorder. “Miscellaneous” included non-genetic congenital etiologies, cerebral ischemia, drepanocytosis, cephalic trauma without temporal bone fracture, etc. CI recipients presenting with the etiologies encompassed between the two vertical dotted lines showed performances around average, i.e. 50% of speech recognition (not statistically different from average). CI recipients presenting with etiologies on the left part of the dotted lines performed significantly below average. CI recipients presenting with etiologies on the right part of the dotted lines performed significantly better than average. Adapted from Blamey et al (in press).</p

Results of the new GLM analysis using ranked speech scores in noise with a CI as the dependent variable.

<p>Results of the new GLM analysis using ranked speech scores in noise with a CI as the dependent variable.</p

Significant effect of Pure Tone Average thresholds of the better ear on the residual percentile rank.

<p>Error bars indicate +/− two standard errors of the mean for each pure tone average range (approximately equivalent to the 95% confidence interval for each mean value shown on the graph; if two mean values fall within one error bar, then the means are not significantly different (p>0.05)). The numbers next to each symbol indicate the number of data points in that range.</p

Significant effect of percentage of active electrodes on the residual percentile rank.

<p>Error bars indicate +/− two standard errors of the mean for each range (approximately equivalent to the 95% confidence interval for each mean value shown on the graph; if two mean values fall within one error bar, then the means are not significantly different (p>0.05)). The numbers next to each symbol indicate the number of data points in that range.</p

Significant effect of brands of CI on the residual percentile rank.

<p>Error bars indicate +/− two standard errors of the mean for each CI brand (approximately equivalent to the 95% confidence interval for each mean value shown on the graph; if two mean values fall within one error bar, then the means are not significantly different (p>0.05)). The numbers of data points for each brand were not indicated to avoid potential identification of the individual brands.</p

Three-stage model of mean expected auditory performance ranking over time for a hypothetical “average CI recipient”.

<p>The detailed description of the Figure is in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0048739#s3" target="_blank">Results</a> section. mHL: moderate hearing loss; s/p HL: severe to profound hearing loss, HA: hearind aid.</p

Results from the 15 five-factor GLM analyses.

<p>Results from the 15 five-factor GLM analyses.</p