Aud 720 Exam 3

external and middle ear, cochlear, 8th nerve

infants and older children who are diff to test w/ behavioral aud

no b/c of underlying neuroanatomic and neurophysioloci bases=supplement with other tests

click=normal ABR and LI functions
(others showed shorter wave V latencies and slight decrease in I-V)

wave V latency increases as HL at 4 KHZ increases

delay in wave I latency and horizontal shift in wave V latency corresponding to the amount of air-bone bone gap

steeper than normal LI function, see minimal latency increase in wave V at high stim intensity levels, despite mod-server SNHL

wave I disappears b/c only more apical regions of cochlea are activated

can use ABR to estimate amy of conductive HL for otitis media w/ effusion-wave I ann latency best indicator

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

usually don't see ABR

wave V LI=steeper than nml, don't see wave V at lower intensity levels

when 1st considered config is better hearing about 1000 Hz thus usually well formed ABR will change as HL is present

Wave V latency delay of about .6-.6 ms
-delay usually greater in males
-wave I/V interval increases with age

increase in absolute latency of I, III, V
prolonged interwave at higher stim rates

latency of V prolonged at all intensities
-Wave V L-I may be indistinugatiable from a conductive

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)

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

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]

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

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

sum of rise, plateau, fall
ex. 2-1-2
-time changes with fq

important to use high pass filter setting of 20-30 Hz to avoid eliminating a sig amount of response

25 ms needed to incorporate increased latencies seen w/ decreasing stim intensity, HL, brainstem and infant path

39.1/s for tones, could go up faster to 61 but not with a 25 ms analysis time

-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
-

-low fq tones are later than those in response to higher fq tones presented at same intensities
-reflect cochlear travel time

early identification of tumors w/in posterior fossa involving 8th cranial nerve

not 100%

4.5-12/100,000 in US=~1%

medulloblastomas
astrocytomas
cranipharyngiomas
ependymommas
pinelamos
gliomas
meningiomas

70% fd in supratentrial compartment of brain (above tentorium and posterior fossa) for adults

70% fd in infratentorial (w/in posterior fossa) for children

invasiveness, size, location and rate of growth

rarely

shwannomas
neurofibromas
meningiomas

• 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)

• 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

• 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]

interwave latency

over 90%

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

often hard to identify individ wave components making latency calculations difficult

-use pt as their own control
-ensure same stim
-usually greater than .3-.4 msec off from normal between ears

degree of HL in 1-4 kHz region

its with large tumors will have no recordable ABR vs its with small 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

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

• Procedure for detecting tumors smaller than 1 cm, which often go undetected by standard clinical ABR methodology

• Derived narrowband ABR technique consists of simultaneous ipsi presentation of broadband click & high pass filtered noise

• 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

= 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

neopalsms and tumors
demyelinatig diseases
f

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

= disease process causes defective myelin metabolism

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

plaques: large, irregular, discontinous lesions, in CNS on myelin sheaths

= sensory & motor deficits in head, limbs, trunk; sphincter disturbances; visual (common), tactile, & hearing (less common) deficits

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

• 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

rare familial abnormalities or myelination formation, found in infants & children & affect white matter

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 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)

may be more prominent than other waves at this time b.c peripheral and system matures before the CNS does

low

females show shorter latency values and larger amplitudes vs males for later wave (III+)=females have shorter interwave latencies

latency increases over range of 25-55 years on the order of .2 msec

low temp = ABR latencies increase
high temp=less studiesd

ex. chloral hydrates don't affect
ex. depressants can affect late potentials

especially important during intraoperative monitoring
need to know how will affect ABR
ABR not seriously influenced by anesthesia

at most causes slight delays in ABR interwave latencies w/o altering morphology

ABR is resistant

II, VII are increased but amps are not affected

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

1. inflexibility in test protocol
2. few carefully defined and published norms
3. data bases might be more for different kinds of specific patients

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)

-limit one page
-always include copies of waves w/ latencies marked and summarized in table
-always include test parameters

1st 2-3 msec after abrupt stamp

consists of 2 sound evoked cochlear potentials and compound 8th cranial nerve action potential
-2 potentials evoked by sound=CM and SM

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

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

with extremely rapid stim and relatively more prominent when recorded w/ high fq tone burst stim

not totally sure but think from outer and inner hair cells

far-field representation of compound AP of 8th cranial nerve
-also referred to as NO
-same as ABR Wave I

synchronous firing of many 8th nerve fibers, thus amp is largest for transient stim with abrupt and rapid rise times

increase amplitude and decrease latency

distal portion of 8th nerve

can get NI as early as 27 weeks
-latency will be prolonged and amp reduced in comparison to adults
-

not must research pertaining to age and gender
-expect presbycusis HL will have an effect

studied in animals
-hypothermia: CMP reduced, latency has little change
-varibale changed for SP

no effect

minimal effect

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)

CM and SP be be generated w/ wide range
-extend duration=SP will persists for duration of stim VS. AP only immediately follows stim

-depends on abrupt onset stim only onset portion of stim contributes to response
-AP not deteced w/ stim rise time of 10msec or greater

range of 0-5/10 msec
-if you only need echo use 5msec
-if you want combo echocg and abr use 10-15 msec

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

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

-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

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

.45 (>45% of AP amp)

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

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.

Wave I=largest amp with click at high intensity
also useful to use transtympanic or ear canal or TM

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

• 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.

• 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 relates to the ability of the test to identify negative results.
Sensitivity relates to the test's ability to identify positive results.

use notched noise
recommended for infants b/c you don't know their HL
only essential for steep losses

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