|
The
cochlear implant program in Sweden
ln 1980, at the urging of profoundly deaf persons, medical
audiologists and otolaryngologists, the Swedish Institute for the Handicapped
initiated a study of the status of cochlear implants in Sweden. The purpose was
to study the different typos of implant, evaluate the reported results, and plan
a strategy for the Swedish cochlear implant program. A study group was
established, consisting of specialists in ENT, audiology and speech research.
The literature was surveyed and implant teams in Vienna, Paris and London were
visited. Members of the study team also attended several international
conferences on cochlear implants and professors Burian and E, Hochmair were
invited to present papers on their work.
In 1983, the Swedish Medical Research Council sponsored a
'state of the art' conference on cochlear implants. Representatives from all
major implant study groups attended As a result of the papers and discussion,
attendees reached agreement that cochlear implants could be considered an
established rehabilitation method for the profoundly deaf adult, However, there
was no agreement regarding ding safety and effectiveness of the operation for
children.
As a result of the conference, a 3 year pilot project was
begun at the Department of Audiology and Otolaryngology at Sodersjukhuset
Hospital in Stockholm, in cooperation with the Department of Speech
Communication arid Music Acoustics at the Royal Institute of Technology.
Assisting in the study were individuals from the Handicap Institute, patient
organizations and the Karolinska Institute. Ten patients were to receive the
Vienna/3M extracochlear implant, then be evaluated as a basis for further
decisions. The study group chose this implant, which does not require surgical
access to the labyrinth, because they were not convinced that better results
would be obtained with intracochlear systems. Also, this choice left open the
possibility of later reimplantation with an intracochlear electrode if it were
proven that such systems gave better results and were not harmful to the inner
ear and auditory nerve.
Preoperative testing
A preoperative evaluation was made to ensure that each
prospective implant patient had been adequately fitted with a hearing aid, had
been trained to use any remaining residual hearing :and received auditory
sensations from electrical stimulation. The quality of these sensations was also
assessed.
After complete otological evaluation, researchers used
audiometry and hearing aid testing to determine the extent of any remaining
hearing. Further testing involved the Swedish version of the MAC test battery, a
speech test using the Risberg and Agelfors (1983) method, vestibular testing, a
CT scan, and electrical promontory stimulation.
Each patient underwent a psychological test battery including
the Defense Mechanism Test, Ravcn's matrices and Q‑sorting. A clinical
interview helped in establishing a psychological profile for each patient and
setting realistic expectations (see below). Finally, patients were required to
perform tests with a vibro‑tactile device, after a short training period.
Each patient's voice was recorded to enable postoperative evaluation of changes
due to auditory feedback from the implant.
All patients who participated in the study met the following
criteria: postlingual deafness, 20-70 years old, no help (or very limited
help) with a hearing aid or vibro-tactile device in the specific speech
tests, realistic expectations, and good motivation.
Postoperative procedure
and rehabilitation
As a part of the postoperative fitting procedures, patients
were first familiarized with the new sounds, then the speech processor was
adjusted to obtain comfortable and equal loudness over the entire frequency
range. During this process, the output signal was limited to prevent patient
discomfort.
In addition to home training after the initial fitting,
patients trained at the Department three times a week for 2 months then twice a
week for 6 months. As the program at the Department progressed a
computer‑aided system that includes most of the MAC test battery was used
increasingly. A home audiotape program with sounds, syllables, words and
sentences was also developed.
Psychological Aspects
An individual's loss of hearing can alter his
self‑image and his interpersonal relationships, as well as his
communication pattern. A cochlear implant may reverse a hearing loss, and yet be
psychologically upsetting.
Some patients who meet the medical
criteria for a cochlear implant have psychopathologies,
including
defective defense mechanisms, that can lead to unexpected complications. Thus,
each patient's psychological status and adaptive capacity must be assessed and
patients should be prepared for their new circumstances. These considerations
are crucial to our continuing efforts to optimize the post‑operative
rehabilitation program.
Implant candidates must be screened to rule out acute
psychological crises. The prospect of recovered hearing generally produces only
positive expectations; patients do not anticipate any new challenges or negative
consequences. In fact, candidates often expect all aspects of life to improve
after implantation. Hence, it is important to determine whether hearing
improvement is likely to make a positive contribution to mental health or
whether unrealistic expectations may ultimately produce negative results.
An adequate general intellectual capacity, especially in the
areas of inductive reasoning and verbal skills, is needed for implant
candidates. Successful adaptation to an implant requires the ability to
correctly interpret new stimuli.
A degree of psychological stability is also needed. Patients
who have extreme psychological reactions to deafness or to the frustrations of
everyday life arc not good implant candidates. To investigate patients' defense
mechanisms and personal adjustment, clinical interviews should be combined with
standardized testing of personality characteristics.
Patient motivation and expectations, both conscious and
unconscious, must be investigated carefully. Patient understanding of the
advantages arid limitations of the implant creates the best chance for
successful adjustment after the operation. Thus, the entire Swedish cochlear implant
team, including the psychologist, helps to inform patients about various
aspects of the implant.
Patients are not the only ones who need to understand the
possibilities and limits of a cochlear implant. Implant patients, like hearing
aid users, are sometimes expected to communicate in situations that demand more
than their limited abilities, notably via telephone. Even the implant team
sometimes expects lo much, creating a burden on the patients. The success of an
implant should be judged by more than just the number of words and syllables the
patient can recognize; contributions to the quality of life should also
be included.
Results
Communication
Skills
Implant recipients in
the pilot project have achieved the following: They have demonstrated an
increase in their ability to detect the presence of sound
and recognize many everyday sounds.
They have developed very good
support for their lipreading; on average they have almost doubled their
communication
skills.
They can
hear their own voices and thereby modulate their speech
better. Half of them can recognize some words without lip-reading and one of the
10 can hold a simple telephone conversation.
During the post-implant training program, the
improvement has been striking for all patients, especially after 6 months.
Further improvement continues 3 years after implantation.
Psychological results
A major change frequently reported by implant recipients is
the feeling of being part of the world again as a result of hearing
the
variety of sounds in normal life. Improved hearing also provides an
improved sense of personal safety. For example, potential dangers can be
detected when walking outside and the presence of others can be detected even
when one is engrossed in some task. The improved sense of safety in return
reduces anxiety, several patients have reported increases in working capacity
and general vitality,
For some patients, a cochlear implant can decrease
dependency, increase confidence, and enable more satisfying patterns in social
relations.
Complications
Of the 10 patients, two had a minor postoperative skin flap
infection. Another patient had small seborrheic wounds in the scalp; one year
after surgery he reported to the hospital with a wound penetrating to the depth
of the receiver and a staphylococcus infection. The receiver and electrodes were
surrounded by pus and granular tissue down to the middle ear, which was itself
completely free of infection. The lesion healed after removal of the implant and
treatment with cloxacillin. The patient was later reimplanted without any
complications.
Two of the early patients suffered a sliding of the
extracochlear electrode because of insufficient support in the mastoid loop. In
later patients this was not a problem because
the technique was changed to direct the course of the electrode so that
it would be supported by bone in the mastoid tip, thus preventing retraction.
The first six patients had a receiver enclosed in epoxy; after three years four
of them experienced a deterioration in hearing threshold and the other two had a
functional failure of the implant. The receivers encased in ceramic material,
used for the remaining four patients, have not deteriorated in the 1.5‑4
years since implantation; in fact, performance has continuously improved.
Three of the patients with the epoxy enclosure were
reimplanted with a Vienna/3M single‑channel intracochlear device,
resulting in lower hearing thresholds and increased dynamic range. The fourth
patient was reimplanted with an intracochlear 22‑channel Cochlear
Corporation device.
Eight out of the ten patients showed no vestibular function
when tested with caloric and rotatoric stimulation before surgery. None of these
had any vestibular symptoms after surgery or at stimulation. Of the two patients
with intact vestibular function, one initially had vertigo after surgery and
during sound stimulation.
Two patients had preoperative periods of severe tinnitus;
this condition was not influenced by implantation. Four of the five patients who
had moderate or slight tinnitus showed some relief after implantation.
Future implantation strategy
That the introduction of a new surgical technique like
cochlear implantation presents risks is apparent. On the other hand the risk of
harm to the patient or deterioration of the remaining neural function of the
cochlea seems small even if an intracochlear electrode is used. No threatening
infections have occurred. However, the effect of replacing electrodes is not
clear. Animal experimentation has shown that the trauma of inserting the
original electrode is small, but the risk of damage from electrode replacement
is greater. Hence, it is very important to use an electrode that will
minimize trauma.
It is interesting that clinical experience does not show any
decrease in performance after replacing electrodes. For the sake of resolving
remaining questions, it is desirable that all future studies be done in a
controlled fashion with careful follow up to ensure reporting of any
disturbances or complications. Standardized hearing tests should be developed to
enable comparison of results between different implantation teams.
|
