Cochlear Implant Mapping

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Cochlear Implant Mapping Powered By Docstoc
					                         By Courtney L. Carver
Those familiar with
the implant process
often hear about the
hook up, activation
day, and getting
mapped. What do all
these terms mean?
An audiologist who
works with cochlear
implant recipients

What Every CI User and
Candidate Should Know
T   he goal of this article is to help
cochlear implant candidates and users
                                                                                              For example, the most common
                                                                                         change after recent activation is a
better understand the mapping proce-                                                     change in loudness levels. Since you
dures and why a well developed map                                                       have not heard for a while, what seems
is important. By reading this article,                                                   loud at first may soon become too
you will know what a cochlear implant                                                    quiet. These appointments help you
(CI) map is, the process involved in                                                     keep the settings optimally adjusted so
mapping a processor, and how the                                                         maximum benefit can be obtained for
map directly affects hearing with a                                                      each individual listener.
cochlear implant.                                                                             Within the first month, there will
     Understanding your role in the                                                      be several mapping appointments
process of developing an ideal map                                                       (see table on page 12). However as
will allow you to use your time produc-                                                  the map stabilizes, the appointments
tively time with your audiologist and                                                    become farther apart. But remember
ultimately help you attain your goals in                                                 that mapping is never finished. It is
staying connected with your implant.                                                     an ongoing process. Adjustments will
                                                                                         need to be made periodically, even
What is a “Map“?                                                                         after many years of use. A cochlear
A map is composed of the individual                                                      implant is a lifetime commitment and
                                             Audiologist Courtney Carver works with      mapping should be completed on an
parameters that a cochlear implant           cochlear implant recipient Joan Kleinrock
user needs in order to have access to        during a mapping session at The Listening
                                                                                         annual basis for maximum benefit.
the rich array of daily sounds. (See table   Center at Johns Hopkins in Baltimore..
on page 12 for details on the parameters                                                 What Else Can I Expect at a
used in developing a map.)                   How Often Does                              Programming Appointment?
     The “mapping” or “programming”          Mapping Occur?                              Each appointment can include audio-
of a cochlear implant is the process         The activation, or “Day One” of hear-       logic and speech perception testing
that sets the best parameters for an         ing, occurs approximately four to six       in addition to mapping. This testing
individual patient. Parameters, or the       weeks after implantation surgery. The       is often done at the beginning of the
settings that define the map, establish      initial activation appointment is the       appointment by using the patient’s
the code that will be supplied to your       first moment of hearing sounds with a       primary map.
implant. This code is a translation of       cochlear implant. However, activation             The purpose of testing is to obtain
the energies that make up sounds and         does not always enable speech under-        some objective baseline measures that
include the coding strategy, the rate        standing. Many users describe those         can be tracked from pre- to post-im-
and duration of electrical pulses, the       initial sounds as sounding like beeps       plant to monitor your progress. These
number of channels and the indivi-           or echoes and are often described as        test scores are also useful in determin-
dual T (threshold levels) and M/C            tinny, robotic or raspy.                    ing subtle decreases over time in the
(most comfortable or loud but                      Each person’s perception of the       case of malfunctioning equipment.
comfortable levels).                         sounds is different. It may take a          In some cases, these tests may help
     The settings of the map are pro-        while to get used to sound and for the      us know where changes are needed
grammed by your audiologist, who is          sounds to take on meaning. Follow-up        in the mapping.
specially trained to judge your respons-     programming is important to taking a
es to test signals to set the program.       cochlear implant to its fullest poten-      The Programming
Each cochlear implant manufacturer           tial. Remember, this is a journey and       Appointment: What
uses different names to describe various     the complexities of the hearing path-       Happens Step-by-Step?
parameters, so things can get confusing.     way require that the hearing process        The first step is for the clinician to run
     It is important to understand           unfolds slowly.                             a standard check on the internal device
how the individual parameters relate               At each programming appoint-          by connecting the speech processor
to one another and that some are             ment, the parameters will be reevalu-       to the programming computer. This
programmed into the implant soft-            ated and adjusted to make sure they         will only take a few minutes. You will
ware and, thus, are not changeable.          are optimized. As you are learning to       not be able to hear this test with your
Since maps are customized to each            hear with an implant, the sounds will       implant and since you will be connect-
individual, they are unique to each          change and the parameters will need         ed to the computer, you won’t hear
person. Different techniques are used        to be adjusted to make sure you have        sounds or voices within the room.
to create maps and are custom fitted         continued improved access to sounds              Next, the “impedances” of
to an individual patient.                    and their range of intensities.                                   continued on page 12

                                                                                                                  July/August 2007 1
Mapping         continued from page 11           an electrode needs to be turned off or     Within the first month, there
                                                 kept on for maximum sound quality             will be several mapping
the contacts in the cochlea will be              benefit. Impedances are often directly      appointments…as the map
checked, establishing communication              linked to certain parameters, making
between the external and the internal
                                                                                            stabilizes, the appointments
                                                 some changes in the software auto-
devices. Impedances measure the ease             matic. Changes in electrode impedanc-    become farther apart…mapping
of current flow through an electrical            es can indicate a change in function      is never finished. Adjustments
circuit or, in this case, a cochlear im-         and can account for changes in sound      will need to be made periodi-
plant electrode. A change in the status          perception. Small changes in imped-      cally, even after many years of
of an electrode could include an open            ances will not affect sound quality or
                                                                                             use. A cochlear implant is a
or short circuit, or just a higher imped-        understanding and are quite common.
ance level.                                            An increase in impedance, but          lifetime commitment and
     In some cases, the audiologist              still within normal limits, means that    mapping should be completed
may need to turn off those electrodes            more stimulation may be necessary to           on an annual basis for
to improve sound quality. This does              achieve the same level of loudness for           maximum benefit.
not mean that the internal device is             the listener. Larger changes in imped-
not working; it just means that that             ances can be caused by ossification      a number of variables which must be
electrode contact may not be providing           inside the cochlea or other physio-      explored to determine the best combi-
good information at that given time.             logic changes.                           nation for each patient. Some variables,
     Don’t panic; the patient and                      As mentioned before, the soft-     such as strategy, rate, and pulse width,
audiologist will determine whether               ware used to program each device has     are set by default in the map. These
                                                                                          defaults largely go unchanged unless it
                                                                                          is necessary due to certain anatomical
                      Sample Programming Schedule*                                        influences, high power requirements,
                                                                                          or a lack of sufficient progress.
  Appointment              Description
  Days 1, 2        Activation of the external equipment;                                  Other Adjustments
                   approximately 4 weeks after surgery                                    Other factors, such as the threshold and
                                                                                          maximal comfort levels, are adjusted at
  1 week           Audiogram and reprogramming
                                                                                          each appointment. The type of task an
  1 month          Audiogram and reprogramming                                            audiologist will ask of the cochlear im-
  3, 6, 9                                                                                 plant recipient varies by manufacturer.
  months           Audiogram, Speech Perception Testing and reprogramming                 Measurements may be made to deter-
                                                                                          mine the softest sound the patient can
  1 year           Audiogram, Speech Perception Testing and reprogramming                 hear (threshold) and the most comfort-
  Every 6-12                                                                              able or loud but comfortable level.
  months           Audiogram, Speech Perception Testing and reprogramming                      The levels set by the patient create
                                                                                          the dynamic range. All sounds picked
                             * May vary by patient and clinician.                         up by the microphone will fall some-
                                                                                          where in this dynamic range, with
                               Select MAP Parameters                                      the softer sounds being closer to the
                                                                                          threshold level and louder sounds
  Name             Description                                                            being closer to the maximal comfort
  Strategy         Set of rules or defaults that dictate how sound is analyzed            level. In some situations, the thresh-
                   and presented. Varies by company.                                      old is set by the computer, rather than
                   Advanced Bionics – Fidelity 120, HiRes P, HiRes S, SAS, MPS, CIS       judged by the patient.
                   Cochlear – ACE(RE), ACE, SPEAK
                   MedEl – CIS+                                                           Electrodes
                                                                                          The audiologist may then go through
  Stimulation      Describes distance between active and indifferent electrode mode
                                                                                          the electrode array, stimulating every
  Rate             Frequency at which electrical current (pulse) is delivered, measured   electrode, in order for the patient to en-
                   in pulses per second                                                   sure the volume of each is set similarly.
                                                                                          Each electrode stimulates a different fre-
  Pulse width      Duration of time electrical current (pulse) is delivered,              quency range and is balanced to ensure
                   measured in microseconds                                               that low pitches and high pitches are set

12 Hearing Loss Magazine
at an even loudness. More changes are         tion than is appropriate (overstimu-       Background noise can never be
made to the map using a live voice.           lation), these measurements can be          eliminated completely—there
     This means that the audiologist          convincing evidence to the audiologist       is simply too much overlap
will turn on the processor to the sound       that levels need to be decreased for        between the characteristics of
environment while it is connected to          better speech perception performance.
                                                                                          background noise and human
the computer. This enables fine-tuning
                                                                                         speech. However, you can give
of the map. Global adjustments can            Going Beyond the Basic Map
be made at this point to change the per-      Once the basic map is finalized, differ-    your brain some time to learn
ceived volume and the sound quality           ent programs can be created for vari-      to filter out the desired speech
can be tailored by emphasizing pitches.       ous listening situations. For example,     from challenging noise and use
                                              programs for listening in background        your lip reading skills to help.
Measuring Stimulation                         noise, listening to music, connecting
of Electrodes                                 to accessories, and talking on the tele-   2) Speak up! If the map is uncomfort-
Objective measures can be used to             phone may be helpful.                         able in any way, tell the audiologist.
determine the approximate level of                  Keep in mind there are limita-          If appropriate, changes can be made
stimulation required for a neural             tions to cochlear implant listening in        at that point that will save you
response. Such measurement capabili-          various situations. The microphone            another trip to the cochlear implant
ties are not always available with older      will pick up all sounds, not just the         center for troubleshooting a week
devices. The most common objective            desired sounds. A map created for use         or two later.
measures utilize the responses from           in background noise may function by        3) Keep in mind that cochlear im-
nerves activated by the device. These         reducing the sensitivity of the micro-        plants give more high frequency
tests can be used to verify behavioral        phone or re-ducing the gain in the low        information than hearing aids.
feedback or to determine approximate          frequency sounds, thereby reducing            Most cochlear implant recipients
levels for the map.                           the volume of the background noise.           notice that voices are more high-
     The ability to obtain objective                However, background noise can           pitched along with most environ-
measures is especially important for          never be eliminated completely—there          mental sounds, especially early
young children and others who have            is simply too much overlap between            on. Much of the clarity of speech
difficulty giving feedback on loudness        the characteristics of background noise       comes from the high-frequency
and sound quality. Objective measures         and human speech. However, you can            information.
can also be used to confirm subjective        give your brain some time to learn to               Remember, better speech un-
measurements in adults. In cases where        filter out the desired speech from chal-      derstanding is the most important
a person is requesting more stimula-          lenging noise and use your lip reading        thing in programming your cochle-
                                              skills to help.                               ar implant, so if your understanding
                                                                                            is improved with increased high-
                                              How Can a Person with a                       frequency information, keep it in
                                              Cochlear Implant Participate                  your program even though it may
                                              for the Best Map?                             not be the sound quality you are
                                                                                            used to or would prefer. In most
                                              There are four important things to            cases, the quality of sound or
                                              keep in mind:                                 “timbre” will improve with time.
                                                                                         4) Recognize that it can take two
                                              1) Trust in your audiologist is               weeks or so to fully adjust to a
                                                  crucial. Follow the audiologist’s         new map. Your brain needs time
                                                  instructions. Don’t try to interpret      to learn the new code that has
                                                  what he or she is asking for…             been programmed into the proces-
                                                  ask questions if you are confused         sor. Patience and practice will
                                                  about what to do. Also, do not try        pay off in an improved listening
                                                  to guess what the “right answer           experience.
                                                  is.” There is no right answer.
                                                  Each manufacturer has a specific       Courtney L. Carver, Au.D., CCC-A, is
                                                  recommendation on what instruc-        a cochlear implant audiologist at The Listen-
                                                  tions to give (most comfortable        ing Center at Johns Hopkins in Baltimore.
                                                  versus loud but comfortable, etc)      She received her Au.D. degree from the
Working with your audiologist during the CI       and this will affect how the map       University of Florida. She works with adult
mapping process can bring positive results.       sounds in the end.                     and pediatric cochlear implant recipients.

                                                                                                                   July/August 2007 13