62 / 224
776
[REV. MED. CLIN. CONDES - 2016; 27(6) 776-786]
Electro-Acoustic Stimulation -
an option when hearing aids are
not enough
Herbert Mauch Biomed Eng. (1), Paul Boyd MD. (1)
(1) Biomedical Engineer. Clinical Technical Research Manager Latin America. Cochlear Latinoamérica. Panama City. Panama.
Email:
hmauch@cochlear.comArtículo recibido: 22-08-2016
Artículo aprobado para publicación: 03-10-2016
SUMMARY
Individuals with steeply sloping high frequency
hearing loss can often hear speech but fail to
understand it, and conventional treatments, including
frequency transposition hearing aids, are usually
ineffective when the hearing loss is severe or profound.
Electro-acoustic stimulation (EAS) is a relatively
new treatment option for this population, in which
mid-high frequency information is provided by a
cochlear implant (CI) inserted into the basal turn of
the cochlea, supplemented by low frequency acoustic
amplification. New atraumatic CI electrode arrays and
surgical techniques have been shown to facilitate low
frequency hearing preservation sufficiently to allow
the use of EAS in the majority of suitable candidates.
Clinical studies have consistently demonstrated
synergistic combination of mid-high frequency
information delivered electrically by a CI with low
frequencies delivered acoustically, providing superior
performance to that obtained from a CI alone.
Key words: Hearing loss, Conventional hearing aids,
electro-acoustic-stimulation.
Introduction
Conventional hearing aids (HAs) represent the standard
of care for the majority of individuals with sensorineural
hearing loss, and are particularly effective when auditory
thresholds are within the moderate-to-severe range. For
very severe losses, however, restoration of speech recog-
nition by HAs has been found to be limited, even when
adequate gain can be provided according to prescriptive
fitting algorithms. This is particularly true for mid-high
frequency amplification, which may even be detrimental
to speech understanding when auditory thresholds are
poorer than around 60-70dB HL (1,2). This is likely related
to the fact that more severe thresholds are associated
with damage to inner hair cells in addition to loss of the
fine tuning function of the outer hair cells, and in extreme
cases there may be total loss of inner hair cells over regions
of the cochlea, i.e. so-called “dead regions” (3).
In many cases of sensorineural hearing loss, auditory thresh-
olds are better for low than for high frequencies. In certain
individuals this threshold difference can be very large -
sometimes with normal or near normal hearing in the low
frequencies and severe-to-profound hearing loss in the
high frequencies. In such cases, high frequency amplifica-