1
Q
what is the limitation of hearing aids?
A
relies on the integrity of the hair cells; the more severe the HL, the less effective a hearing aids will be
2
Q
what are CIs?
A
sophisticated implantable device that attempts to restore useful hearing to severely hearing impaired individuals
3
Q
goal of CI
A
acoustic input –> convert to electrical signal –> interpreted by brain as sound
4
Q
how do CIs send signals via the aud nerve to the brain?
A
by electrically stimulating the surviving nerve fibers in the cochlea w/ an electrode array
5
Q
what are the 3 dimensions sound are distinguished by?
A
amplitude (intensity)
frequency (spectral)
time (temporal)
6
Q
frequency is conveyed by
A
- place in the cochlea that is stimulated
- enables pitch perception by stimulating the aud neurons in localized, narrow regions of the spiral ganglion
7
Q
amplitude is encoded by
A
- current level
- enables intensity (loudness) perception by changes in amplitude of stimulus current
8
Q
temporal cues extracted from input and are conveyed by
A
- stimulation rt and pattern of stimulation
- enables processing of temporal cues
9
Q
primary benefits of a CI
A
increased aud perception (mild HL range)
10
Q
secondary benefits of a CI
A
- enhancement of lip reading skills, speech perception and speech production
- psychological effects
- lifestyle and social effects
11
Q
possible limitations of CI
A
potential loss of residual hearing
12
Q
- provides electrical stimulation to one point of contact in the cochlea using one electrode
- more aware of environmental sounds
A
single channel CI
13
Q
electrical stimulation to multiple points of contact in the cochlea using multiple electrodes
A
multi-channel CI
14
Q
- picks up sound from environment
- transduces the sound to an electrical signal
- sends signal to sound processor
A
microphone
15
Q
- sound goes from pre-amplifier to processor, where sound is analyzed and converted to digital signal
- selects and arranges sounds picked up by mics
A
sound processor
16
Q
send electromagnetic signal through skin to the receiver under the skin
A
transmitter cable (and the electromagnetic RF coil)
17
Q
converts electromagnetic signal to digital code/electric pulses, which are then sent to the electrode array
A
receiver coil
18
Q
stimulate the aud nerve directly, which sends signal to brain where it is perceived as sound
A
electrodes
19
Q
located in center of external coil and internal coil, adheres to the external RF coil to the head and directly over the internal coil
A
magnets
20
Q
RF signal serves as
A
power supply for the internal stimulator
21
Q
receives signals from speech processor and converts them into electric impulses
A
transmitter and receiver/stimulator
22
Q
- group of electrodes that collects the impulses from the stimulator and sends them to different regions of the aud nerve
- contains metal electrode contacts placed in ionic fluid (perilymph)
- controlled amount of current applied to electrode contact causes ionic current to flow causing potential changes in fluid immediately surrounding electrode
A
electrode array
23
Q
official FDA approved age for CI’s in children is
A
12 months of age
24
Q
12-24mos candidacy audiometric criteria
A
profound sensorineural HL bilaterally
25
>2yrs-17yrs candidacy audiometric criteria
severe-to-profound sensorineural HL bilaterally
26
adults: 18yrs + candidacy audiometric criteria
- AB and Med-EL: severe-to-profound SNHL bilaterally
- Cochlear and Medicare: moderate to profound SNHL bilaterally (PTA 70 or greater)
- 50% or less on sentence recognition tests in ear to be implanted and 60% or less on non-implanted ear
27
less than 40% correct in best aided condition on a sentence recognition test
medicare criteria
28
audiometric candidacy recommended test battery
az bio sentences (in quiet and noise +10/+5)
CNC monosyllabic words
BKB-SIN
29
term to describe implanting those pts that do not fall within the general candidacy guidelines
off-label implanting
30
does candidacy = success?
no, success is measured against individualized goals based on the pt
31
what does the FDA say you must do to assess candidacy for CI?
- unaided audiogram
- hearing aid trial
- sentence recognition test with hearing aids
32
a patient's best listening condition, the condition that yields the highest % correct scores on listening tests
best aided condition
33
- assesses the performance of adults with cochlear implants and to improve comparability of performance results across centers
minimum test speech battery original (MTSB)
34
- provide a reliable and efficient measure of speech reception threshold for sentences in quiet and in noise
- determines the reception threshold for sentences
HINT
35
harder than HINT
| 10 talker babble noise by different talkers
az bio sentences
36
has a modified adaptive approach
| sentences are presented at a fixed level and four talker babble is presented increasingly more difficult SNRs
BKB SIN
37
- not required for FDA candidacy but gives a good picture of aided ability w/o context cues
- develop lists of monosyllabic words
constant/nucleus/constant test (CNC)
38
degree of HL implant ear
poorer hearing ear
39
speech reception scores implant ear
poorer wrs
40
duration of HL implant ear
most recent onset of deafness is often selected
41
anatomical considerations implant ear
most normal appearing scala tympani
42
vestibular weakness implanted ear
implant ear with weakness
43
most systems place the electrode array in the
scala tympani through round window or fenestration near the round window
44
why scala tympani?
accessible & relatively close to the spiral ganglion cells
45
depth that electrode array is inserted into scala tympani?
22-30mm within the cochlea
46
of fibers activated is a function of
the amplitude of the stimulation current
47
loudness can be controlled by
varying amplitude of the stimulation current
48
primary goal of electrode arrays
sufficient insertion while reduction insertional trauma
49
magic # of electrodes
8
50
what can too many electrodes lead to?
redundancy btwn electrodes and decrease their ability to deliver distinct sound frequencies
51
close placement to what is desirable in getting better selectivity?
modiolus
52
- pre-curved shape for intention to maintain proximity to modiolus, placed along the medial wall of the cochlea
- can result in greater insertion trauma
- shorter (inserted 360-420º)
- lower current levels; more efficient battery life
perimodialar array
53
- insertion along the lateral wall of the scala tympani
- do not damage the modiolus or spiral ganglia (more preserved residual hearing)
- can be inserted up to 720º (can reach apical end of cochlea)
- requires greater power
straight (lateral wall) electrode array
54
frequency coding is constrained by
- # of surviving aud neurons
| - spread of excitation associated with electrical stimulation
55
- remote reference electrode serves as reference, current flows btwn them
- spread of excitation is larger
- all electrodes are activated at the same time
monopolar
56
- two intracochlear electrodes reference each other
- active and reference (ground) electrodes are placed close to each other
- more localized stimulation
- some electrodes are simultaneous and some are sequentially stimulated
bipolar
57
goal of spatial specificity of electrodes
maximize the # of non-overlapping populations of neurons to be stimulated
58
- all electrodes are activated at the same time
| - monopolar
fully simultaneous
59
- some electrodes are simultaneous and some are sequentially stimulated
- bipolar
partially simultaneous
60
- occurs when electrodes are activated in sequence, one after another
- requires pulsatile stimulation
non-simultaneous/pulsatile
| monopolar or bipolar
61
simultaneous stimulation drawback in CI?
- limited frequency specificity
| - channel interaction
62
in CI, channels are defined by
bandpass filters
63
when two adjacent electrodes are stimulated simultaneously with complimentary waveforms, effectively targeting the area btwn them
virtual channel
64
signal processing goals
- maximize speech understanding
| - make all sounds as naturally sounding as possible
65
overview of processing
4 BPF --> 4 channels --> rectifier --> LPF --> generate pulses --> amplitudes proportional to envelope
66
types of pulses used to be delivered to the electrodes?
biphasic pulses
67
why do CIs use biphasic pulses?
to achieve the non-simultaneous stimulation by varying the timing
68
- non-simultaneous processing strategy
- frequency of pulse train is fixed
- all electrode contacts are stimulated in each cycle of stimulation
continuous interleaved sampling (CIS)
69
neural responses to stimuli from one electrode may be significantly distorted by stimuli from other electrodes
channel interaction
70
number of electrodes stimulated =
of bandpass filters
71
electrodes can be stimulated in ______ in order of six-three-five-two-four-one which maximizes the spatial separation btwn stimulated electrodes
staggered order
72
2 methods that can be used to extract the envelopes of filtered waveforms
- rectification
| - hilbert transform (med-el) = feature extraction
73
- high-rate CIS strategy
- can be delivered non-simultaneous or partially simultaneous to 16 electrode contacts
- uses higher cut off frequencies for low pass filters
- uses half-wave rectification rather than full wave rectification
- all electrode contacts are stimulated in each cycle of stimulation
HiRes
74
goal of Hi-Res
improvement in provision of fine temporal structure
75
- stimulate on the channels with highest amplitude inputs
| - goal: capture strongest components of a speech signal and discard low fluctuations in amplitude
N of M strategy
76
- larger # of bandpass filters
- produces better spectral representation but poorer temporal
- uses up to 20 filters that span a wider frequency range
- stimulates as many as 10 electrodes in a cycle
- adaptive stimulation rt in order to preserve spectral as well as temporal info
- based on temporal frame
SPEAK
77
- fast rate SPEAK strategy
| - higher stimulation rt typical of CIS and the methodology of SPEAK to highlight specific frequencies
ACE
78
key difference between SPEAK and ACE
- rt of stimulation
| - ACE is high (more similar to CIS)
79
CIS type signal coding that provides better access to fine temporal structure
fine hearing processing (FSP)
80
dynamic range of aud thresholds vs electrical pulses
100dB vs 10-20dB
81
- shift everything up
| - everything sounds higher pitched
frequency mismatch
82
rt that would result in aud nerve response more typical to that of a normal aud system
2000 pps
83
speech is audible yet comfortable, and provide loudness perception of speech and environmental noise
stimulation level
84
setting lower limits of electrical dynamic range
stimulation threshold
85
an estimation of the threshold
interpolation
86
to increase stimulus intensity
- increase the amplitude by increasing the upper limit of stimulation
- widen/lengthen the pulse width bc the stimulus then stays on longer - temporal summation
87
equal sense of loudness across electrode array
loudness balancing
88
ensure that stimulation does not result in loudness discomfort, unfavorable sound quality, or non-auditory percept
sweeping
89
info critical speech understanding
high frequency
90
fine structure info, needed for localization of sound and appreciation of music
low frequency
91
can make gain modifications on an individual electrode or successive electrodes
frequency shaping
92
allows 2-way transmission of data through radio frequency communication to and from the internal implant
telemetry
93
what is electrode impedance influenced by?
cochlear fluid
94
- excessively low impedance
- there's not enough resistance
- two electrodes touching each other
short
95
- excessively high impedance
- too much resistance
- ossification; physical barrier
open circuit
96
T or F: normal electrical impedances do not imply that the electrode contacts are in the cochlea
T
97
what can we do if electrodes are out of voltage compliance?
lower the amplitude of the stimulation current
98
what if you dont want to change the loudness?
widen/lengthen the pulse width - provide more stimulation to your pt without having to increase the current level
99
when programming or mapping a pt, what is the goal?
setting the electrical dynamic range
100
what measure do we set on each electrode to achieve this?
EDR allows us to ensure sounds are audible, make sure sounds are comfortable, and adequate loudness growth
101
when would subjective measures (setting threshold and upper limits of stimulation) in a CI user not be possible or reliable?
younger pts and those that are cognitively impaired
102
- early latency evoked potential from electrically stimulated aud nerve fibers
- stimulation is a biphasic pulse
- measured through telemetry
ECAP
103
- represents the lowest level at which electrical stimulation elicits a stapedial reflex
- most commonly used objective measures
ESRT
104
after cochlear implantation, ABR can be performed by electrical stimulation through the cochlear implant
EABR
105
CI surgery
- incision behind ear
- mastoidectomy
- drill the facial recess for access to promontory and round window
- two structures you must drill btwn is the facial nerve and chorda tympani
- surgeon places receiver stimulator
- electrode array is inserted through an opening in cochlea
106
opening or hole in cochlea
cochleostomy
107
benefits of round window insertion
- accurate placement: directly to scala tympani
| - no drilling in cochlea
108
chorda tympani
regulates taste
109
risk of surgery
- anesthesia (issues w pts w cardiac problems)
- injury to facial nerve
- meningitis
- CSF leak
- perilymph fluid leak
- infection
- blood or fluid collection
- attacks of dizziness or vertigo
- tinnitus
- taste disturbances
- numbness
- reparative granuloma
110
must have what vaccination before surgery?
meningitis
Cochlear Implants
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