audiology evoked potentials

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ASSR reflects: (auditory steady state response)
-an ongoing response to continuous overlapping stimuli
-phase locked to modulation
as opposed to response to onset of stimulus in ABR
What is mismatch negativity?: Test wich is elicited by a physically deviant stimulus in a sequence of homogenous standard stimuli (oddball paridigm)
-thought to be automatic mismatch process between the sensory inflow created by the stimuli & the memory trace of the standard stimuli
What is ABR: (Auditory Brainstem Response)
an auditory evoked potential that repressents neural activity from the VIII cranial nerve and auditory pathways of the brainstem to the level of the inferior colliculus
- a series of vertex-positive waves that occur within 15ms of the onset of stimulus
Automated identification of waveforms may use?: -computer algorithms developed for peak identification
-highest amplitudes in latency regions where peaks are expected in normal ABR
-similarity to normal template
What is common mode rejection?: evoked potential recordings , recorded between 2 electrodes. Differential amplifiers subtract differences in voltage between pair of electrodes (Cz-A1)
TEOAEs: low intensity sounds detected in the external ear canal by a microphone that occur in response to a brief stimulus or click
DPOAEs: Occur in response to a stimulus but represent distortions of the stimulus. Distortion products appear at several frequencies when 2 primary tones are applied to the ear (F1&f2) This pair of tones is swept across a frequency range (1k-6kHz) as each pair is presented, measurements are made at 2f.-f2 frequency to determine amplitude of DPOAE
The IPL or interpeak latency of wave I-V is often termed...: The central conduction time or BS transmission time.
-Because Wave I is generated by the auditory nerve at the periphery of the aud system and wave V is presumably generated by the LL as the enter the IC = conduction time through the auditory BS
Prevalance of AN/AD auditory neuropathy/dyssynchrony: 1 in 10 of those with severly abnormal ABR
Risk factors for AN/AD: Hyperbilirubinanemia anoxia/hypoxia estreme prematurity (
JCIH comprehensive assessment recommended after/during audiological diagnosis AN/AD: Petiatric & development evaluation
otologic eval with imaging of cochlea (CT and Auditory Nerve MRI)
medical genetics evaluation
opthalmologic eval
neurological eval
communnication assessment
AN/AD natural history: -may stay the same, worsen or improve
-ABR may recover & be consistant with the behavioral threshold with normal morphology
-If problem due to maturation, recovery would normally be complete within 18 months if not suspect another cause for AN/AD
-some cases perceptual ability seems to improve although ABR remains abnormal
-OAEs which have been present may disappear.
Management of AN/AD: Variability - management counseling
-Information & support for family
-repeated assessment
-behavioral thresholds annually
- electrophysiology - repeat ABR,CM OAE betwee 8-10 mos, 9-15 mths
-tymps & reflexes
-assess development of communication
When recording early potentials it is essential to distinguish a low amplitude response from higher background noise. how is the accomplished?: By averaging a large number of responses together and time locking the onset of the stimulus with the onset of the computer analysis sweep. This allows the evoked potential of interest to be summed while the background noise because of its random nature, averages toward zero and thus is attenuated.
For ABR Why use click presentation rates that are odd numbers?: 11.1 or 27.7/sec
to avoid repitition rates that are multiples of 60 Hz which could introduce power line artifact into the response
Patients with AN demonstrate disruption of function at the level of?: IHCs and or auditory nerve in the presence of normal outer hair cell function
most patient with AN show bilateral symptoms but not all
What is the purpose for doing EOAEs?: -site of lesion identification
-cross check other tests
-prediction of audiometric configuration
-They reflect cochlear function at level of OHCs
-presence requires normal middle & outer ear functioning
What does it mean if OAEs cannot be evoked?: -could mean occluding cerumen in ear canal
-could mean middle ear pathology
-could be the noise floor is hiding the response
-The inner ear may not be functioning normally
How do infant OAEs differ from adults?: -infants have robust amplitudes of about 20dB
-age 4 response drops to about 15dB where adults are 10dB
-difference could be due to anatomic changes in the outer or ME systems that occur w/development
-ear canal diameter & length increase w/ development as does volume
-differences in the efferent neural systems of the adult and infant.
Response must be above 6dB to pass
By convention the 2 tones used to elicit distortion product otoacoustic emissions are?: f1 & f2 primary tone frequency
absolute level of primary tone= 65-55 dBSPL
The distortion measured at 2f1-f2
Similarities between ABR and ASSR: -both record bio-electrical activity
-both may use similar electrode arrays
-both are classified as auditory evoked potentials
-both use similar transducers (inserts)presenting controlled acoustic stimuli
The primary goal in the evaluationof ABRs is to record a clear & reliable Wave ___: Wave I
- which is the landmark for the remainder of the interpretation of peripheral auditory function
Representation of ABR waves? Wave I Wave II Wave III Wave IV Wave V: I = CAP of the distal end of the VIIIth nerve
II = proximal end of the VIII
III = CN
IV = SOC
V = LL and IC
ABR findings with conductive HL?: Will usually demonstrate good wave morphology, normal interwave latencies but will have markedly delayed wave I
ABR findings with sensory HL: Will have poor wave morphology, weak or small & delayed Wave I.
-interwave latencies will be normal
ABR findings for neural HL: normal wave I, overall poor morphology, interwave latencies delayed.
Wave I-III delayed latency
How do ABR results differ in infants and adults?: Infants - waveform shows less morphology. Absolute & interpeak latencies tend to be prolonged initially but should be adult like by 18-24 months in patients with normal auditory development
Later potentials have ABR (early potential): -higher amplitudes
-0.1 to 0.5 micro volts
Click ABR can estimate hearing sensitivity in what freq range?: 2000-4000 Hz but ABR does not represent conscious hearing
-Normal ABR wave form = 5-7 peaks from 1.4 to 8.0 ms after the onset of a stimulus
The waves of ABR represent: sums of neural activity from 1 or more sources of various discrete points in time
-latency of ABR waveforms is the most reliable and robust characteristic and provides the core of ABR interpretation
Unlike some other evoked potentials the time between peaks of ABR does not reflect conduction time but are formed by multiple responses from various generators and can be used to judge what?: brainstem integrity not travel time from one nucleus to another

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