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111 Cards in this Set

  • Front
  • Back
peripheral aud system
external and middle ear, cochlear, 8th nerve
who is ABR most useful in for perish assessment
infants and older children who are diff to test w/ behavioral aud
is ABR ever a valid measure of hearing
no b/c of underlying neuroanatomic and neurophysioloci bases=supplement with other tests
low fq sensory HL
click=normal ABR and LI functions
(others showed shorter wave V latencies and slight decrease in I-V)
mid and high fq SNHL
wave V latency increases as HL at 4 KHZ increases
characteristic for finding conductive losses
delay in wave I latency and horizontal shift in wave V latency corresponding to the amount of air-bone bone gap
sensory losses
steeper than normal LI function, see minimal latency increase in wave V at high stim intensity levels, despite mod-server SNHL
what happens at low intensity levels for sensory losses
wave I disappears b/c only more apical regions of cochlea are activated
otitis media
can use ABR to estimate amy of conductive HL for otitis media w/ effusion-wave I ann latency best indicator
otosclerosis
genetic disease of bone around cochlea
-could use air and bone conducted in ABR w/ severe conductive HL b/c they have make a masking dilemma
severe to profound cochlear pathologies
usually don't see ABR
mod high fq SNHL
wave V LI=steeper than nml, don't see wave V at lower intensity levels
Meniere's endolymphatic hydrops
when 1st considered config is better hearing about 1000 Hz thus usually well formed ABR will change as HL is present
presbycusis
Wave V latency delay of about .6-.6 ms
-delay usually greater in males
-wave I/V interval increases with age
noise induced SNHL
increase in absolute latency of I, III, V
prolonged interwave at higher stim rates
in general aud nerve and/ or brainstem disorders
latency of V prolonged at all intensities
-Wave V L-I may be indistinugatiable from a conductive
how can you distinguish conductive from retrocochlear
comparing latencies of earlier peaks of ABR
in conductive HL all waves will be offset by equal amounts vs. in retro earlier peaks may be w/in nml limits or if there is perish HL delayed by lesser amount than the later components (prolonged interweave)
misconceptions about tone ABR
1. tone ABR thresholds are not similar to behavioral thresholds
2. ABR to 500 Hz tones are poor predictors of low fq behavior thresholds
3. waveform identification of ABR to 500 Hz is difficult
who is it not true that ABR thresholds are NOT similar to behavioral thresholds
1. not true b/c: w/normal hearing listeners, tone-evoked ABR thresholds are typically 10-20 dBnHL
2. those w/SNHL are typically 5 to 15 dB higher than pure tone behav thresholds for adults & from 10 dB lower to 10 dB higher than pure tone behav thresh in infants & young children
3. Recently, high correlations (i.e., = 0.94) have been demonstrated between ABR thresholds to 500-, 2000-, and 4000-Hz air-conducted tones in notched noise and the pure-tone behavioral thresholds for these frequencies for infants and young children (N=88) with normal hearing or sensorineural hearing loss
4. Regression line slopes were close to 1.0, indicating nearly a one-to-one correspondence between increases in pure-tone behavioral threshold and increases in ABR threshold. [Stapells, Gravel & Martin, Ear & Hearing, 1995]
why is it not true that ABR to 500 Hz tones are poor predictors of behavioral thresholds
1. not true b/c data has indicated that ABR to 500 Hz brief tones DOES provide an acceptably accurate assessment of pure tone behav thresh
3 methods for fq specific ABR
1. mask fq regions not intented to be part of stim (high pass noise/noise/notch in region desired/masking with a pure tone)
2. response to stim @ specific fq or w/ a defined fq region is served from 2 other responses (derive response method)
3. use a tonal stim w/ careful onset characteristics
stimulus duration of tone ABR
sum of rise, plateau, fall
ex. 2-1-2
-time changes with fq
filter settings of tone abr
important to use high pass filter setting of 20-30 Hz to avoid eliminating a sig amount of response
analysis time of tone ABR
25 ms needed to incorporate increased latencies seen w/ decreasing stim intensity, HL, brainstem and infant path
stim rate of tone ABR
39.1/s for tones, could go up faster to 61 but not with a 25 ms analysis time
morphology of tone ABR
-consists primaily of V and negativity V'
-typc don't see I-IV at low-mod intensities or high intensity
-resposnes to tones occurs later than clicks
-
latency of tone ABR
-low fq tones are later than those in response to higher fq tones presented at same intensities
-reflect cochlear travel time
most powerful neurodiagnsositic application of ABR
early identification of tumors w/in posterior fossa involving 8th cranial nerve
how sensitive/specificiity is ABR
not 100%
annual incidence of 8th cranial nerve
4.5-12/100,000 in US=~1%
intracranial neoplasms (list)
medulloblastomas
astrocytomas
cranipharyngiomas
ependymommas
pinelamos
gliomas
meningiomas
general location of tumors for adults
70% fd in supratentrial compartment of brain (above tentorium and posterior fossa) for adults
general location of tumors for children
70% fd in infratentorial (w/in posterior fossa) for children
impact of tumors depends n
invasiveness, size, location and rate of growth
subjective aud complaints in its with brain tumors
rarely
8th nerve tumors types (list)
shwannomas
neurofibromas
meningiomas
shwannomas
• Most common of 8th nerve tumors
• 80% of cerebellopontine angle neoplasms = Schwannomas (occurrence = 5-10% of tumors)
• schwannomas occur in females more than males (age range = 35-60 yrs)
• schwannomas of 8th nerve = usually benign – arise from a focal point w/in nerve trunk of peripheral portion of vestibular branch, tumor expands, tumor = encapsulated mass projecting from side of nerve [figure 12-1 Hall]
• grows toward CP angle, they can grow to be rather large (4-5 cm)
• usually grow slowly & can spontaneously stop growing
• most common complaint = hearing loss (also can report headache, dizziness/imbalance, unsteady gait, tinnitus)
neurofibromas
• Disease = neurofibromatosis (von Recklinghausen’s)
• Has a peripheral form (NF1) or central form (NF2)
• Genetically transferable & autosomal dominant
• NF1 = more common than NF2, either can be bilateral (NF2 is more often bilateral than NF1)
• NF1 occurs in 1st decade of life vs. NF2 in 2nd or 3rd decade
• 8th nerve tumors fd in 5% of NF1 patients & in over 95% w/NF2
• in both types, tumors arise from Schwann cells – NF1 is similar to Schwannomas, just discussed – displace nerves vs. NF2 – engulf nerves, also NF2 tumors are not encapsulated
• usually see HL in over 90% of patients w/neurofibromatosis
• disease has progressive disabling & disfiguring course
meningiomas
• Originates from meningothelial arachnoid cells & often fd attached to dura
• Slow growing
• >90% fd in supratentorial compartment, >67% fd in anterior ½ of cranium
• if involve 8th nerve, difficult to distinguish from Schwannomas
• almost always fd singly, may produce subtle audiometric signs, but ABR findings are unequivocally abn
• [figure 12-2 Hall]
diagnostic paratmeter w/ ABR for tumors
interwave latency
how many surgically confide tumors cab be identified with ABR abnormalities
over 90%
normal vs. abnormal latency criteria for retrocochlear
1. Abs latency of wave V exceeds clinical definition of nml limits
• 2. abnormal interear or interaural latency diff for wave V – wave V latency for one ear vs other (value greater than 0.2-0.4 msec)
• 3. wave I-V latency = abn prolonged relative to norms, can also look at I-III & III-V [figure 12-3 Hall]
• 4. abn interaural latency diff for I-V (also maybe for I-III, III-V) – looking between the ears
problem with ABR retrococlear
often hard to identify individ wave components making latency calculations difficult
wave V interaural latency difference
-use pt as their own control
-ensure same stim
-usually greater than .3-.4 msec off from normal between ears
important consideration for likelihood of wave V presence vs. absence
degree of HL in 1-4 kHz region
general rule for size of tumors
its with large tumors will have no recordable ABR vs its with small tumors
contralateral effects of 8th nerve tumors
• 1. ABR interpretation of contralateral effects must be differentiated from abnormalities due to bilateral tumors or if waves I or III are not clearly recorded to other serious hearing impairment
• 2. ABR recordings from contralateral ear may provide diagnostically useful info on tumor size & functional effects, even though degree of hearing deficit on involved ear precludes meaningful ABR recording
how can a tumor interfere with generation of ABR?
1. compression or stretching of 8th nerve fibers by expanding tumor mass resulting in desynchronization of 8th nerve fibers or increased resistance in nerve conduction velocity
• 2. Compromised blood supply to 8th nerve & cochlea
when do you use stacked ABR
• Procedure for detecting tumors smaller than 1 cm, which often go undetected by standard clinical ABR methodology
what is the stacked ABR technique
• Derived narrowband ABR technique consists of simultaneous ipsi presentation of broadband click & high pass filtered noise
how does this stacked ABR technique work?
• Portion of cochlea masked by high pass noise does not contribute to ABR
• Cutoff freq of high pass noise lowered successively from one run to next
• Narrowband contributions from cochlea are then derived by successive subtraction of responses to successive high pass noise masking conditions [figure 2 Don]
• [figure 3 Don] wave V latencies are longer for each successive (lower center freq) derived ABR – reflect cochlear response time composed of apparent TW delay & freq dependent synchronization time
what does the stacked ABR method do?
= minimize cochlear response time on amp measures, amp of wave V in unmasked response varies depending on wave V time delay between derived bands that compose unmasked response, variations in delay alter degree of synchrony of activity betw diff regions of cochlea which in turn affects amp of wave V
• stacked ABR created by time shifting derived band waveforms so peak latencies of wave V in each derived band coincide & add these together
list of CNS abnormalities
neopalsms and tumors
demyelinatig diseases
f
neoplasms and tumors
brainstem glioma
• Most often found in children or adolescents
• ~ ¾ of brainstem tumors in children = gliomas
• grow slowly & are highly invasive – thus total surgical removal often not possible & recurrence is often likely
• ABR abnormalities are consistently recorded in children w/pontine brainstem gliomas
dysmelinating
= disease process causes defective myelin metabolism
most common dymelinating diseases
MS
MS
• Onset betw 20-40 yrs (50-70% patients)
• MS rare in children
• Male:female ratio = 1:1.7
• More prevalent in colder climates (don’t know why)
• Disease has slow progressive course that is irregular – fluctuating periods of exacerbation & remission of specific symptoms
what do you look for in MS
plaques: large, irregular, discontinous lesions, in CNS on myelin sheaths
what are the symptoms of MS
= sensory & motor deficits in head, limbs, trunk; sphincter disturbances; visual (common), tactile, & hearing (less common) deficits
ABR findings of MS
prolonged interwave latencies (I-III, III-V, I-V); dec amp –esp wave V; poor morphology (desynchronization) for later wave components; poor test repeatability; total absence of one or more recognizable wave components after wave I or II – most often wave V; occasional absence or prolongation of wave I; most characteristic finding = inc ABR latency esp for wave V
Schilder disease
• Progressive childhood disease, usually have bilateral, large, continuous patches of demyelination & associated severe axonal damage
• Also known as diffuse cerebral sclerosis
• Some consider this childhood MS
• Diagnosis made by CT scan & CSF exam
• Symptoms = irreversible, progressive loss of intellectual functions, cortical blindness, bilateral spastic paresis, & deafness – death in 1-5 years
leukodystrophies
rare familial abnormalities or myelination formation, found in infants & children & affect white matter
leukodystrophies ABR findings
prolonged interwave I-V latency, absence of wave III or V, or all components after waves I & II, wave I usually present but ABR is rarely nml
ABR at birth
• ABR waveforms are incomplete at birth
• Generally only 3 major components seen (I, III, V)
• Interwave latency values are initially prolonged (I-III, III-V, I-V)
• E.g. I-V at term birth = ~5.00 msec vs. what for an adult?? (4 msec)
wave I at birth
may be more prominent than other waves at this time b.c peripheral and system matures before the CNS does
ABR at _____ fq stimuli are more impt for generating ABR in newborns than adults
low
gender effect on ABR
females show shorter latency values and larger amplitudes vs males for later wave (III+)=females have shorter interwave latencies
age effect on ABR
latency increases over range of 25-55 years on the order of .2 msec
body temperature on ABR
low temp = ABR latencies increase
high temp=less studiesd
sedatives and hypnotics on ABR
ex. chloral hydrates don't affect
ex. depressants can affect late potentials
anesthetic agents
especially important during intraoperative monitoring
need to know how will affect ABR
ABR not seriously influenced by anesthesia
halothane and isoflurant
at most causes slight delays in ABR interwave latencies w/o altering morphology
nitrous oxide
ABR is resistant
alcohcol
II, VII are increased but amps are not affected
what is calibration and why do we do it
calibration=adjustment of equipment or application of defined correction factor when using equipment.
why we do it=should do it periodically to ensure properly functioning equipment
problems with relying on published norms
1. inflexibility in test protocol
2. few carefully defined and published norms
3. data bases might be more for different kinds of specific patients
how to establish normative data base
1. must establish how analyze waveform amp and latency (ex. peaks, shoulder ext) (draw diagrams to aid)
2. for ABR: minimally want values for I, III, IV and interweave latencies, V/I ratio
3. some equipment has software to aid
4. establish norms using cutoff criterion for normality (usually 2-2.5 stdev above mean value for normal subject group)
case reports
-limit one page
-always include copies of waves w/ latencies marked and summarized in table
-always include test parameters
when does ECochG occur
1st 2-3 msec after abrupt stamp
anatomic and physicologic bases of EcOCHl
consists of 2 sound evoked cochlear potentials and compound 8th cranial nerve action potential
-2 potentials evoked by sound=CM and SM
CM
alternating current potential that follows waveform of stim; pure tone produces it in a sine like way
-arises from OHC
-reflects OHC activity from basal end of BM
-best evoked by single polarity stim
SP
direct current potential recorded following a continuous tone or tangent stim
-more prominent when recorded w/ high fq tone burst
-shift in baseline of recording
when is SP clearly observed
with extremely rapid stim and relatively more prominent when recorded w/ high fq tone burst stim
SP from
not totally sure but think from outer and inner hair cells
AP
far-field representation of compound AP of 8th cranial nerve
-also referred to as NO
-same as ABR Wave I
what does the AP reflect
synchronous firing of many 8th nerve fibers, thus amp is largest for transient stim with abrupt and rapid rise times
what happens to the AP with increases in stim intensity
increase amplitude and decrease latency
AP from
distal portion of 8th nerve
infancy and childhood ECohG
can get NI as early as 27 weeks
-latency will be prolonged and amp reduced in comparison to adults
-
advancing age ECoHG
not must research pertaining to age and gender
-expect presbycusis HL will have an effect
body temp ECohG
studied in animals
-hypothermia: CMP reduced, latency has little change
-varibale changed for SP
attention.arousal on ECohG
no effect
muscular artificat and ECOhG
minimal effect
effect of stim FQ on ECohG
SP is direct current shift receptor potential
-SP follows envelope of stim
-AP component most often generated w/ CLICK stim (possible to use filtered clicks or shaped tone burst)
stim duration and EchoG
CM and SP be be generated w/ wide range
-extend duration=SP will persists for duration of stim VS. AP only immediately follows stim
AP stim duration
-depends on abrupt onset stim only onset portion of stim contributes to response
-AP not deteced w/ stim rise time of 10msec or greater
analysis time for EchoG
range of 0-5/10 msec
-if you only need echo use 5msec
-if you want combo echocg and abr use 10-15 msec
montage for EchoG
noninverting electrode=tiptode
inversiting electrode=mastoid/earlop ipsis to stim or contra to stim
if you have non and in on same sade for ECochG may yield smaller AP amp
filters for EChoG
CM reflects stim polarity and fq=filter settings must be wide enough to encompass signals
-typically use bandpass filter setting of 3-10 Hz or 1500-3000 Hz
stim factors EChoG general
-AP latency dec slightly and amp increases as stim intensity increases
-SP not seen at lower intensity levels
-CM only present w/ mono phasic stim polarity (rare or condense)
-increase stim rate will eventually reduce AP amp vs. SP will remain unchanged
-morphology changes dramatically with click vs.tone burst and also for low vs. high fq tone hurts
EChoG uses
1. objective indentation of Menieres/hydrops
2. enhancement of wave I and identification of I-V interweave interval in presence of HL or less than optimal recording options
3. monitoring of cochlear and aud serve function during surgical procedures that place ear at risk for permanent damage
SP/AP ratio of ___considered abnormal
.45 (>45% of AP amp)
stimulus parameters effects on ABR
1. increase intensity=decrease latency and increase amplitude

2. rate= Fast stim rates will increase latencies of all components and the decrease amplitude of the earlier components.


3. frequency

4. polarity=condensation, rarefraction, alternating
• rarefraction=later latencies
When and why to mask
Mask whenever it is loud enough to cross over. It would look like a normal ABR when it should be normal when it should be abnormal. Just put in 50 dBnHL to the nontest ear.
how to make Wave I best
Wave I=largest amp with click at high intensity
also useful to use transtympanic or ear canal or TM
Why should u do ABR before CT/MRI
Should do ABR first because it is readily available, inexpensive, noninvasive, office procedure w/ proeven high sensitivity, and may reflect small lesions not visible with CT
What are contralateral recordings used for:
• Determine presence and location of wave I by comparison to contra recording and obtain better definition of waves IV and V b/c they tend to be more separating in contra-recordings.
Transducers
• TDH-39: need to eliminate electromagnetic arificated by using shielding earphone
• THD-49: better suited for AEP esp for high fq or click
• ER-3A: travel time in tube, must correct (.9), less artifact b/c transducer is away from electrode, less ringing, no collapse canals
• Bone vibrator: restricteded intensity range, use most successfully in newborns, must be aware of occlusion effect
specificity
sensitivity
Specificity relates to the ability of the test to identify negative results.
Sensitivity relates to the test's ability to identify positive results.
what kind of masking to use for tone ABR
use notched noise
recommended for infants b/c you don't know their HL
only essential for steep losses
when to use bone
if you wanted to determine conductive HL
used most successfully in newborns and young children
-expected down to 20 dB for 500 Hz and 30 dB for 2000 Hz