The objectives of this study were to determine if the triphasic stimulation pulses strategy can eliminate facial nerve stimulation (FNS) in cochlear implant (CI) users, and to determine the required change(s) in fitting parameters and patient performance with triphasic strategy.
Method: Subjects were five CI users with FNS that could not be eliminated by other methods. They were 4 males and one female. All fitting parameters (THR, MCL, Compression, Sensitivity, Maplow, etc.) and patient performance (Aided Thresholds and SRT) were re-measured with triphasic strategy and compared to the biphasic strategy.
Results: Triphasic pulse stimulation strategy eliminated FNS in all subjects and showed better patient performance than biphasic stimulation pulses strategy, but required modifications in fitting parameters to achieve patient satisfaction.
Conclusion: Triphasic stimulation is highly effective way to eliminate FNS in the CI users.
Cochlear implant (CI) is a medical electronic device that was invented to help patients who have sensorineural hearing loss to restore normal hearing or near to normal hearing via electric stimulation of the auditory nerve endings inside the human cochlea. CI is a partially implanted solution which consists of internal and external part. The Internal part is named the implant and the external part is the audio processor which is worn over the ear, receives sounds, analyses them, and send it to the internal implant. As Mudry & Mills  mention in 1961, the first CI was implanted by William House and John Doyle in Los Angeles, California. Since then, the number of CI is tremendously increasing across the world. From 30 June, 2012-30 June, 2013, approximately 50,000 cochlear implants were sold. Given the world population of about seven billion, this means that roughly seven cochlear implants per million individuals are sold each year. Approximately 30,000 of these 50,000 cochlear implants were received by children. Some of these children received bilateral implants, which means that 25,000 individual children received unilateral or bilateral cochlear implants. Children and adults who are deaf or severely hard-of hearing are main recipients of CI. As of December 2012, approximately 324,200 registered devices have been implanted worldwide. In the United States, roughly 58,000 devices have been implanted in adults and 38,000 in children as Kamal  mentioned. After the internal part (the implant) is implanted in the patient head and the wound is totally healed, the implant is switch on and fitting sessions begin to program the audio processor. After variable umber of programming sessions over a period 3-6 months, the vast majority of CI recipients are able to hear normal or near normal.
Hearing is one of the sensory systems of the human body. It is part of the communication skills that human has. It is curtail for every body for everyday life. Any hearing problems or disability may affect the quality of life. Ear is the main organ that responsible for hearing sensation. It consists of three main parts outer ear, middle ear and inner ear. The sound waves is picked up by the pinna and directed towards the external ear canal, the sound waves hit the ear drum at the end of the external ear canal
and causes the ear drum to vibrate. The ossicles which are at the
middle ear and attached from one side to the ear drum start also
to vibrate. Through their shape, physical properties, and the way
they connect with each other amplify the vibrations. The ossicles
are the malleus, incus and stapes. The malleus is directly attached
to the ear drum and the stapes is attached to the cochlea through
a window which is named oval window. The vibrations finally
propagate inside the cochlea which is filled with fluid. When this
fluid vibrates, it causes displacements at the basilar membrane
where the organ of corti is. Organ of corti has hair cells that
respond to any displacement in the basilar membrane and start
firing electrochemical pulses that are picked up by the auditory
nerve. Figure 1 illustrates the ear anatomy. Normal hearing
covers a frequency range of sounds between 20Hz and 20,000Hz.
The majority of speech sounds are within a frequency range of
between 100 and 8000Hz. The human ear is most sensitive to
frequencies around 1000–3500Hz. Hearing loss can be classified
into main four types: conductive, sensorineural (SNHL), mixed,
and neural. There are also several causes of hearing loss in each
In such type of hearing loss, sound vibrations are not
reaching the cochlea with all its power. There is a pathology
that is blocking or delaying the sound vibration to reach the
cochlea, leading to a reduction in ear sensation to sound. This
pathology can be fluid, blood, pus, or adhesions in the middle
ear. The middle ear pathology can be caused by infection or
trauma. Ear trauma can also leads to ossicular discontinuity.
Excessive ear wax in the external auditory canal can also lead
to conductive hearing loss. Conductive hearing loss can be cured
by medications, surgeries or using hearing aids or combinations
This kind of hearing loss happens when there is pathology
in the cochlear sensory cells (outer and inner hair cells) or its
vascular supply (stria vascularis). In such case, the cochlear
sensory are not responding in a normal way to the vibrations
of the basilar membrane and fail to transduce such vibrations to
electrical pulses that can pass through the auditory nerve. This
leads to hearing loss of varying degrees. This kind of hearing loss
cannot be surgically or medically treated as the damage of the
hair cells is usually irreversible. Hearing aids are the usual line
of management for SNHL. However, in cases of severe degree of
SNHL, hearing aids cannot restore hearing. In such cases CI is
the best line of management. The most common cause of SNHL
in children is congenital, usually of genetic etiology but it can
be acquired due to insults to the cochlea in the early neonatal
period. Examples of such insults are neonatal hypoxia, neonatal
infection and neonatal hyperbilirubinemia. Other causes of
SNHL include ototoxic drugs, severe head trauma, presbycusis,
and chronic exposure to load sounds.
This kind of hearing loss occurs when there are two
components of conductive and SNHL that causes hearing loss.
It results from problems in both the inner and outer or middle
ear. Treatment options may include medication, surgery, hearing
aids or hearing implants.
The hearing loss is also classified according to its degree
into mild, moderate, severe, and to profound hearing loss;
(Figure 2). The degrees of hearing loss can be determined just
by looking into the patient’s audiogram. An audiogram is a
graph illustrating a person’s usable hearing and the amount of
hearing loss that an individual has for each ear. The audiogram
illustrates the degree of hearing sensitivity and hence the degree
of hearing loss at each sound frequency from 250Hz to 8000Hz,
as a standard. CI is indicated when there is severe, severe to
profound or profound degree of hearing loss. When the degree
of hearing loss is less than severe, hearing aids are beneficial.
As mention in MED-EL that cochlear implant (CI) is a medical
electronic device that is indicated for patients who have severe
to profound hearing loss. CI is the only medical device capable of
replacing a sense. It works by bypassing non- functioning parts
of the inner ear and providing electrical stimulation directly to
nerve fibres in the cochlea. CI consists of internal part (Implant;
Figure 3) and external part (Audio processor; Figure 4 The
internal part consists of internal coil, magnet, electronic package,
and electrode. While the external part consists of control unit,
coil, magnet, coil cable, battery pack and battery pack cover. As
Kamal  mentioned there are mainly three cochlear implants
manufactures; MED-EL based in Innsbruck-Austria, Cochlear
based in Australia, and Advanced Bionics based in United States. Cochlear Corporation device uses 22 electrodes spaced along its
array; Advanced Bionics implant has a 16 element array, while
the MED-EL electrode has 12 pairs of electrodes (each pair
sharing the same position along the array).
Figure 5 illustrates how CI works. Sound is collected by the
microphone embedded in the external audio processor which
processes the sound signal through some complicated analog
and digital algorithms and then sends the signal to the internal
part through radio frequency waves through the processor coil.
The internal part under the skin receives and demodulates the
signal and sends it to the electrode that was implanted inside
the cochlea. Each electrode consists of numbers of contacts;
each contact is responsible of some range of frequencies and
stimulates the neural cells in some way to match the incoming
sound as Kamal  mentioned, the electrical signals cause
activity of the fibers of the auditory nerve, and the brain
interprets this as sound.
A sound coding strategy describes in detail the way this is
carried out. As MED-EL mentions that Sound coding strategies
can vary in how efficiently aspects of the sound signal are
transmitted, and what priority is given to these aspects. These
variables of sound coding strategies have a direct effect on the
quality of the hearing experience. There are two types of coding:
Coding by place: It corresponds to the tonotopic arrangement
of the cochlea. Like the keys of a piano, the cochlea is arranged
in order of frequency and in normal hearing, each place along the cochlea responds best to a certain frequency. The base of
the cochlea responds best to high frequencies, whereas the apex
responds best to low frequencies. The pattern of activity in both
the auditory nerve and the brain match this arrangement. Figure
6 shows such tonotopic organization of the cochlea. The audioprocessor
of the CI analyses the incoming sound and spilt it into
different frequencies and send each frequency component to its
corresponding place in the implanted electrode that contacts a
corresponding place of the auditory nerve within the cochlea.
By this way, CI preserves the normal tonotopic arrangement of
Code by rate: The second fundamental mechanism of sound
coding in normal hearing is coding by rate. In the cochlea the
hair cells are responsible for converting the movements of the
membrane in the cochlea into electrical impulses. Due to the
way the hair cells respond to this movement, the firing pattern
of the auditory nerve activity closely corresponds to the timing
pattern of the sound signal. This process works well in normal
hearing for frequencies up to ~1 kHz. As frequency increases,
the efficiency of phase locking decreases, until about 4–5 kHz,
where phase locking no longer operates MED-EL . Figure
7 shows how the cochlea preserves the rate of the incoming
sound. To a large extent, CI mimics the cochlear in preserving
the rate of the incoming sound. Since stimulating multiple
electrodes at the same time can give an unpredictable loudness
percept because of channel interactions (addition of stimulus
voltage fields) most current commercial coding strategies use
sequential stimulation. The rate of pulse stimulation to an
electrode depends on processing strategy. The slowest pulse
rates in use are 200 pulses/s (pps). A pulse rate of around 800
pps is common to several strategies, while higher rates of up to
5000 pps can be used in some recent strategies. With pulsatile
stimulation within these ranges of rate, the percept is not of a
burst of pulses, but rather as a continuous signal.
Cochlear implant candidacy criteria have evolved
dramatically since multichannel implants were first approved
for adult use by the FDA in 1985 and in 1990 for the pediatric
population. Initially, only individuals with bilateral profound
sensorineural hearing loss with no open set speech recognition
were considered candidates for cochlear implantation. Over
time, however, these criteria have become less stringent and
individuals with greater amounts of residual hearing are now
being implanted Gifford & René . Currently, the candidacy
of cochlear implant is usually divided according to the age
(pediatric or adult).
Figure 8 displays the evolution of audiometric criteria
of CI adult candidacy over the years to the most current
encompassing region of audiometric thresholds for moderate
sloping to profound sensorineural hearing loss. Initially, CI was
restricted to adult deaf patients with profound degree of SNHL
(i.e., hearing loss more than 90dB HL) Gifford & René . After
the success of CI in such category, CI was recommended for
patient with only severe degree of hearing loss (from 70dB HL to
90dB HL), for whom hearing aids did not help. CI had excellent
results in such degree of hearing loss. Finally, CI is currently
indicated for patients with only moderate degree of SNHL at
the lower frequencies and severe to profound degree at higher
frequencies. In such case, the external audio-processor works as
hearing aid in the lower frequencies and as the processor for CI
in the high frequencies. Such scenario is referred to as electroacoustic
stimulation or hybrid stimulation.
Children are the main recipients of CI. Currently CI is
permitted for children with severe to profound hearing loss and
of the age of one year and older. A trial period of hearing aid
for 3 to 6 months is required before the CI surgery. In addition,
CT scan and MRI to check the status of the cochlea and auditory
nerve is also required.
Two to four weeks after the CI surgery, the audio-processor
has not have to be programmed to deliver the optimal electrical
impulses to the auditory nerve. The ultimate goal of device programming is to adjust it so that it can effectively convert
acoustic input into a usable electric signal for each electrode
stimulated. With proper programming, the device converts the
acoustic signals (speech and non-speech signals) into electrical
pulses and delivers them to the auditory nerve terminals
within the cochlea, and to maintain the specific parameters of
the acoustic signals similar to what the normal cochlea does
to a large extent. Proper programming is critical to achieve
the ultimate goals of CI which are normal speech perception
and hence development of oral language in cases of children.
The most crucial aspect of programming a cochlear implant
is to establish the lowest and highest usable stimulation level
for each electrode in the array, and this is a common feature of
all cochlear implant manufacturers as Kamal  mentioned.
Therefore, two basic psychophysical measures need to be
obtained on each intracochlear electrode: electrical thresholds
(THR or T level), defined as the softest level at which a patient
is stimulated 100% of the time, and most comfortable loudness
levels (MCL, C or M levels), defined as the loudest sound a patient
can listen to comfortably for a sustained period of time Shapiro &
Bradham . The range in dB between the lowest intensity that
can be coded within the auditory nerve and highest intensity
represents the electrical dynamic range. Such electrical dynamic
range is very limited when is compared to the acoustic dynamic
range of speech (around 100dB). The challenge of the CI audioprocessor
is to compress the wider acoustic dynamic range to
the much smaller electrical dynamic range. This is achieved by
specific characters within the processor which are the Automatic
Gain Control (AGC) and the instantaneous input dynamic range
(IIDR). Such compression is crucial for speech perception.
As Kamal  mentions in his study, the most important
fitting parameters are listed below. It must be noted that these
parameters are somehow strategy and device dependent. Some
parameters are presented in different devices under different
names. Almost all of these parameters are used in the fitting of
all three manufacturers’ implants.
a. MCL, M level, or C level is the most comfortable
stimulation level that the CI recipient can tolerate
b. TRL or T level is the softest stimulation level that the CI
recipient can detect.
c. Stimulation current: It presents the current amplitude
that is given to each electrode; it is calculated differently
from one manufacturer to another.
d. Phase duration: The duration of applying every single
pulse, it is named also pulse width.
e. Charge Unit: It is the product of stimulation current
and the phase duration, actually this is what CI recipient
f. Pulse rate: The number of pulses that is given to the cochlea every second.
g. Frequency bands: dedicated frequency range presented
by each electrode.
h. Coding strategy: The sound coding protocol applied on
the signal inside the speech processor.
i. Maplaw: It controls the progress of amplitude growth
function and its compression characteristics.
j. Sensitivity: It defines the sensitivity of the speech
processor microphones. It is the range that the microphone
k. Directionality: Several microphone modes which
control the incoming signal to eliminate noises and mimic
l. Compliance level: This is the maximum power the
implant can give at each channel.
The surgery is performed under general anesthesia and
takes approximately 1 to 3 hours. The procedure is considered
a routine surgery with low risk. In this part, it is presented the
general steps of CI operation, risks and complications.
General steps of CI surgery (American cochlear implant
a. Skin opening: The surgeon will make a 4-6cm incision
behind the ear in a double flap technique.
b. Mastiodoctomy: The surgeon opens the mastoid bone
leading to the middle ear space; it is the best and most direct
way to access the middle ear.
c. Posterior Tympanotomy: Also known as facial recess,
Opening a window from the mastoid to the middle ear
between the facial nerve and the chorda tympani.
d. Round window opening: The surgeon then makes an
opening in the round window of the cochlea or near to it
e. CI placement: The surgeon then places the receiver/
stimulator, the electronic portion of the device attached
to the electrode array, under the skin behind the ear and
secures it in place.
f. Electrode insertion: The implant electrode array is
then inserted into the cochlea.
g. Skin closure: The incision is then closed and a head
dressing is applied to protect the incision.
Cochlear implantation surgery risks are the same or lower than
other common ear surgeries. Rarely the following can occur:
a. Bleeding and/or swelling at the incision site.
b. Infection in the area of the implant
c. Ringing (tinnitus) in the implanted ear.
d. Dizziness or vertigo (typically resolves within a few
days after surgery).
e. Change in taste/dry mouth (typically resolves within a
few weeks or months after surgery).
f. Numbness around the incision site
g. Injury to the facial nerve.
Pain tolerance is different for everyone, but in general the
pain is mild-to-moderate and can be controlled with oral pain
medications, if needed, for a few days. During the posterior
tympanotomy, the surgeon is very close to the facial nerve and
corda tympani that why it is very important in the operating
room to have facial nerve monitoring machine. This machine is
monitoring if the surgeon accidentally touches the facial nerve
while drilling or not and will give alarm if this happened. If the
surgeon does damage the facial nerve, the patient will have
a facial nerve paralysis and will affect half of the patients face
macules. Also if any damage occurs to the corda tympani, the
taste sensation of the patient will be badly affected. These effects
are permanent and irreversible. Therefore, facial nerve monitor
machine is considered to be mandatory in the cochlear implant
Stimulation mode refers to the electrical current flow,
that is, the location of the reference electrode relative to the
active stimulating electrode. Monopolar stimulation refers to
a remote ground reference (outside of the cochlea). Figure 9
shows this monopolar stimulation in MEDEL implant, where
the ground electrode lies in the implant under the skin while
the actual active electrodes are implanted within the cochlea.
In bipolar stimulation, both the active and ground electrode is
within the cochlea. For the Cochlear manufacture, the device
can be programmed in both monopolar and bipolar stimulation
mode while the Advanced Bionics and MED- EL devices can be
programmed in a monopolar mode only. Typically monopolar
stimulation is the preferred mode, as this mode may extend
battery life, allowing for a more consistent thresholds and
threshold value for adjacent electrodes due to a wider current
spread. In addition, this mode is more suitable than bipolar
in the interpolation of THR and MCL levels in populations in
whom obtaining psychophysical measure on every electrode
implanted is not feasible Shapiro, Bradham and William . In
all the three CI manufacturers, the CI stimulates the auditory
nerve with series of short biphasic electrical pulses. The pulses
are biphasic because the net current through the tissue should
be zero to avoid unwanted long-term electrochemical effects as
Kamal  mentioned in his study. Figure 10 shows the biphasic
pulse stimulation in MED-EL CI. Recently, MED-EL introduced
another way of stimulation with several different pulse shapes
and different inter pulse gaps. They are called triphasic pulse
and precision triphasic pulses (Figure 11).
Post-implantation facial nerve stimulation is one of the wellknown
and most frequent complications of the cochlear implant
procedure. Some conditions, such as otosclerosis and cochlear
malformations, as well as high stimulation levels that may be
necessary in patients with long auditory deprivation expose
patients to a higher risk of developing post-implant facial nerve
stimulation. Facial nerve stimulation following CI occurs when
the electrodes inside the cochlea are activated and the facial nerve
gets wrongly stimulated too. This non- auditory stimulation is
not desired in the CI process. Facial nerve stimulation following
CI occurs in 6.5% CI users. There is no difference in rate of
occurrence of the facial nerve stimulation among the three CI manufacturers. Some anatomical factors contribute to such unwanted
facial nerve stimulation. These factors include that the
implanted electrode pass across the facial recess, making them
very close to the facial nerve. The electrical current may spread
from the CI electrodes and stimulates the facial nerve. This occurs
more frequently because the CI electrode is inserted inside the
cochlea and the facial nerve (labyrinthine portion part) is passing
near the cochlea near the basal and med turn of the cochlea. So
sometimes its gets wrongly stimulated. It was also hypothesized
that the array of electrodes could erode the bony layer between
the scala tympani and facial nerve, making the electrical current
passing through CI electrode closest to the facial nerve Berrettini
et al. . Other factors responsible for facial nerve stimulation
are low impedance pathway at the modiolar base, high
stimulation levels necessary to stimulate hypoplasic auditory
nerve, malformed cochlea, or malfunctioning electrodes. Facial
nerve stimulation is more common in patients with otosclerosis
receiving CI as the new soft and remodeled bones have lower
impedance. Facial nerve stimulation causes severe discomfort
for the patients and their families because of the twitches of the
facial muscles specially the lid muscles leading to eye closure
with sounds. It is frightening to the parents in case of children.
Functionally, facial nerve stimulation degrades the performance
of CI users and badly affects their speech perception.
Facial nerve stimulation can frequently be resolved with
changes in some parameters in the audio- processor fitting
but, in some cases, this can lead to a reduction in the patient
performance Berrettini et al. . Three common clinical
remedies to prevent unpleasant FNS caused by activation of
certain electrodes are to expand their pulse phase duration,
simply deactivate them or decrease the MCL Bahmer & Baumann
In this solution the audiologist or the programmer searches
for the electrodes that cause FNS and switch them off. However,
if more than one electrode causes FNS, this will cause more and
more electrodes to be switched off. The more the switched off
electrodes, the worse the patient performance is. Moreover,
switching of many electrodes will affect frequency resolution
of the CI and will degrade the speech discrimination of the
patients because each electrode supply electrical pulses to
specific frequency region. At MED-EL implants, for example, it is
recommended to keep at least eight electrodes out of twelve on
for good patient performance.
It was found that the more the phase duration or the pulse
width of the biphasic pulse, the less probability of FNS occurs.
But the drawback of widening the pulse width is the decrease of
pulse rate per second which will decrease the spectral resolution
of the speech signals and degrade the speech discrimination of
Of course, this is a straight forward solution, but it will
dramatically affect the patient performance directly by not
coding substantial segment of speech signals according to their
loudness. Unfortunately, in some patients these methods do not
provide sufficient FNS prevention and limits the benefits of CI.
The main objective of the current study was to evaluate
the effect of applying the triphasic pulse stimulation in
minimizing or eliminating the FNS in CI recipients. Other
objective was to determine whether applying the triphasic
pulse stimulation requires change(s) in the fitting parameters
of the audio-processor (specially the MCL) to get the best
patients performance. Final objective was to determine the
effect of applying the triphasic pulse stimulation on the
patient performance as measured subjectively from the patient
satisfaction and objectively by measuring the aided pure tone
audiometry and aided speech discrimination.
Table 1 shows the relevant data of the subjects included in
the current study. Five CI recipients were included to this study.
Four of them were implanted by MED- EL Synchrony Flex28
and one subject was implanted with MED-EL Synchrony Form
24 and all the subjects use Sonnet audio processor the external
part. They were four males and one female with age range of 4 years to 36 years. Years of implantation ranged from 2 years
to 4 years. Four subjects had bilateral profound SNHL and one
subject had single sided deafness. Hearing loss was diagnosed
in infancy in two subjects (congenital SNHL). One subject had
bilateral progressive SNHL; one subject had post-traumatic
sudden SNHL; one subject had sudden unilateral profound
SNHL. The radiological findings were normal CT and MRI scans
for all subjects except S4 has malformed cochlea IP2. All subjects
were implanted by the same surgeon and by the same surgical
technique. The CI electrodes were inserted via round window
with no injury to the FN during the operation.
All subjects experienced FNS from second or third session
after the switch on session. FNS was at all channels. CT scan was
performed post-operative to check and confirm the electrode
placement inside the cochlea. Table 2 shows different methods
used and failed to complete elimination of FNS in all subjects
before the application of triphasic pulse strategy. Methods
included decrease MCL, deactivate some channels in one subject,
and increase pulse width.
The MCL, THR, other fitting parameters and audiological
performance was registered before and after applying triphasic
pulse stimulation. (Figures 12-16) show MCL, THR, PTA and
SRT for the five subjects in the biphasic and triphasic pulse
stimulation. Figure 17 shows the same data averaged among
the five subjects. In all subjects, triphasic pulse stimulation
eliminated FNS in all electrodes except in 2 electrodes in one
subject. All subjects were satisfied with this strategy with
improvement in both aided pure tone threshold and SRT.
In this subject all electrodes were working and causing FNS.
Figure 12 shows MCL, THR and aided audiogram before and
after applying triphasic strategy are shown. Both MCL and THR
had to be increased to achieve satisfactory map, which resulted
in better aided pure tone threshold and better SRT (the SRT
improved from was 35 dB to 30 dB).
In this subject all electrodes were working except electrode
twelve (it was found out of the cochlea). FNS was in all eleven
electrodes. Similar to subject 1, MCL and THR had to be increased
to achieve satisfactory map, which resulted in better aided pure
tone threshold and better SRT (the SRT improved from was 50
dB to 25 dB). In such subject, the improvement in the aided SRT
was better than in subject 1.
Subject 4 demonstrate same findings as previous subjects
with elimination of the FNS and increase in both MCL and THR
to achieve satisfactory maps. Not like the pervious subjects the
triphasic inter-pulse gap had to be increased to 20 microseconds
(the default value is 2.1 microseconds). Also, the Maplaw
compression was changed from 500 to 700 to reach the patient
satisfaction. The first four THR values were set to zero. The SRT
improved from 40 dB to 30 dB.
In this subject all electrodes were working except electrodes
eleven and twelve they showed no response (they were switched
off). Similar to subject 4, triphasic inter-pulse gap was increased
to 20 microseconds (it was 2.1 microseconds), and the Maplaw
compression was changed from 500 to 700 to reach the patient
satisfaction. The first four THR values were set to zero. Both
aided pure tone and SRT was improved after the triphasic pulse
stimulation. The SRT improved from 35 dB to 30 dB.
In average, the MCL values had to be increased from 5-10
units (across electrodes) with triphasic strategy the satisfactory
maps. The THR values vary between both strategies. It is clear
that with using the triphasic strategy the aided thresholds and
the SRTs become better. Aided thresholds improved by average
of 10 dB and also the SRT improved by more than 10 dB. In
addition, inter-pulse gab might be increased to 20, and the
compression value to 700 (found in two subjects but need more
investigations and more subjects).
The benefits of CI for patients who suffer from SNHL
bilaterally or even unilaterally are outstanding. But, sometimes
the fitting of these patients has drawbacks. One of these drawbacks is FNS. It is a very disturbing problem and limits the
usage and benefits of CI. Triphasic stimulation pulses strategy
was invented by MED-EL to eliminate or minimize FNS. The
objectives of the current study were to test the effect of triphasic
strategy in eliminating FNS and to determine the required
change in fitting parameters and patient performance after
applying the strategy. Results showed that triphasic stimulation
eliminated FNS in all subjects and in all electrodes except in
two electrodes in one subject. Moreover, patient’s performance
was better in triphasic strategy than in the traditional biphasic
strategy. All subjects were satisfied and had better aided pure
tone threshold and SRT. The MCL had to be increased to achieve
patient satisfaction and the optimal maps. Such increase in
the MCL might increase power consumption and might lead to
change the power source more than biphasic strategy (needs
more investigations). It is mandatory to repeat the current study
in much larger sample. If same results were obtained, then it is
highly recommended to use the triphasic pulse stimulation in
cases of FNS as the first line of management to eliminate FNS as
it gives better performance than the other methods to eliminate
FNS as decrease MCL, increase pulse width, and deactivation
of the channels. A disadvantage of triphasic strategy is that
the fitting parameters (especially MCL and THR) must be remeasured
to achieve the optimal maps and patient satisfaction.
Another point that deserves study with triphasic stimulation
is the need to increase in the inter-pulse gap in some patients
to achieve the patient satisfaction. Increase the inter-pulse gap
might decrease the pulse rate and may have a direct impact on
speech discrimination .
Triphasic pulse stimulation is highly effective way to
eliminate FNS in CI users with better patient performance than
the traditional methods. Actually, this method should be the first
option or solution the audiologist should pick up with patients
who have FNS. But the audiologist has to take into account the
modifications that should be done to the fitting map parameters.
The MCL values are higher in triphasic maps compared to
biphasic ones. This study should be performed on a larger scale
and should take into account the other triphasic parameters like
inter-pulse gap and precise triphasic pulses.