70 / 224
784
surgery was 21.5dB and 16.5dB in the CI422 and Hybrid L
recipients respectively, increasing to 30dB and 22dB after
12 months. Seven CI422 users who lost residual hearing
showed significantly superior CI alone and bimodal perfor-
mance than that obtained by three Hybrid L users who also
lost hearing. The authors therefore concluded that there is
a degree of trade-off in the choice of electrode length in
terms of likely hearing preservation and outcomes if residual
hearing is lost. However, the studies by Lenarz et al. (16) and
Skarzynksi et al. (26) both demonstrated that the bimodal
condition for subjects using the CI422 together with
residual hearing in the non-implanted ear (implanted ear
blocked) provided substantially improved performance rela-
tive to the preoperative condition. These findings suggest
that the Slim Straight array of the CI422 and CI522 devices
provides an effective combination of hearing preservation
and CI-alone performance in potential EAS users as well as
offering an effective option for conventional CI candidates.
Conclusions
1.
Individuals with steeply sloping high frequency hearing
loss can usually hear speech but fail to understand it.
Conventional or frequency compression acoustic hearing
aids have been shown to be relatively ineffective in providing
a useful auditory signal when mid-high frequency hearing
loss is severe or profound.
2.
Prospective CI recipients with low frequency (up
to 500Hz) audiometric thresholds better than around
70-80dBHL are candidates for electroacoustic stimulation
(EAS), whereby a CI is implanted into the basal turn of the
cochlea in order to provide mid-high frequency informa-
tion and acoustic amplification is provided to stimulate
residual low frequency hearing. Such candidates are usually
implanted in the poorer ear when there is functional preop-
erative hearing.
3.
A range of thin, flexible CI electrode arrays have been
shown to preserve residual hearing within levels commen-
surate with EAS in the majority of recipients. The Cochlear
Slim-Straight array, as used in the CI422 and CI522 devices,
provides good hearing preservation performance yet is long
enough to provide high levels of CI-alone performance even
if residual hearing is lost.
4.
Clinical studies have consistently demonstrated syner-
gistic combination of mid-high frequency information
delivered electrically by a CI with low frequencies deliv-
ered acoustically, providing superior performance to that
obtained from a CI alone. The observed enhancement of
CI-alone speech recognition by acoustic low frequencies
has been shown to be effective when delivered to the side
ipsilateral or contralateral to the CI.
5.
New integrated external sound processors, such as the
Cochlear CP900 series, are able to deliver electrical and
acoustic signals from a single unit, providing enhanced
convenience for the user and better integrated fitting
procedures.
Conflict of Interest
Herbert Mauch is employee of Cochlear Latinoamerica, Paul Boyd is consultant for Cochlear Europe.
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