EP final

extra peaks
bifid wave I
fused peaks

wave I has 2 closely spaced peaks
more likely to happen with fast stimulus rate

2 peaks combine into a single wave complex
most often fused are waves IV and V
wave IV appears as a hump, short plateau

peaks that are reliable but smaller in amplitude than major peaks

absolute latency patterns
interwave latency pattern
amplitude patterns

AC: tone burst, click
BC

1. Mask frequency regions not intended to be part of the stimulus
2. Responses to stimulus at specific frequency or with a defined frequency region is derived from two other responses
3. Use a tonal stimulus (spectrally constrained stimulus)

increase intensity: latency decreases, amplitude increases
decrease intensity: latency increases, amplitude decreases

frequency
duration: sum of rise time, plateau time, fall time
intensity
rate: # of stimulus presented/second
polarity: direction of waveform

interstimulus interval
interval between successive stimuli can be determined by dividing discrete time period by # of stimuli presented within that period
short ISI: can decrease amplitude, increase latency

stimulus onset produced by movement of transducer diaphragm toward TM

pressure wave in negative direction produced by movement of transducer diaphragm away from TM

8th cranial nerve, cerebellopontine angle, extraaxial pathology

-early identification of tumors within the posterior fossa and involving the 8th cranial nerve
-use ABR to differentiate between cochlear and retrocochlear hearing loss

-use in combo with ECochG
-diagnostic parameter with ABR=interwave latency

-undetectable responses at max stim level even though patient may have no or a mild-mod hearing loss
-usually find this in patient with large tumor

1. Absolute latency of wave V exceeds clinical definition of normal limits
2. Abnormal interear or interaural latency difference for wave V
3. Wave I-V latency abnormal prolonged relative to norms
4. Abnormal interaural latency difference for I-V

patients with large tumors will have no recordable ABR vs. patients with small tumors

location of tumor
consistency of tumor
status of blood supply
rate of tumor growth

-procedure for detecting tumors smaller than 1 cm
-derived narrowband ABR technique consists of simultaneous presentation of click and high pass filtered noise

when you suspect a small tumor

portion of cochlea masked by high pass noise does not contribute to ABR
-cutoff freq lowered each run
-narrowband contributions from cochlea are derived from subtraction of responses to successive high pass noise masking conditions

longer for each successive derived ABR
-reflects cochlear response time composed of TW delay

created by time shifting derived band waveforms so peak latencies of wave V in each derived band coincide and add these together

age effects
body temperature
attention/state of arousal
drugs

ABR waveforms incomplete at birth
-may only see I, III, V and interwave latency values are prolonged
-during 1st 18 months, other components emerge, III and V shorten in latency

ABR is essentially adult like in latency and amplitude

-low freq stimuli better
-increased rate produces more pronounced increase in ABR latency

-latency increased over age range of 25 to 55 (0.2msec)
-I-V interval increases over age range 60-86

females show shorter latency values and larger amplitudes vs males for later waves (III, IV, V, VI) so interwave latencies are shorter for females

when temps exceed 1 degree of normal (98.6,37) is a factor in affecting recordings

effects less studied than low temp

latencies increase because synaptic transmission is delayed, anoxal conduction velocity is decreased
-temp <14-20 degrees ABR disappears

0.2 ms for every degree below average for I-V latencya

0.15 ms for every degree increase above normal for I-V latency

ABR recordings are independent of state of arousal and attention
-gives ABR an advantage in evaluating periperal/central aud function in a wide variety of patients

can use ABR to monitor effects of ototoxic drugs if behavioral testing not possible

-chloral hydrate: no effect
-phenobarbitol: can increase variability in late potentionsl

ABR components can be obscured by excessive muscle artifact

adjustment of equipment or application of defined correction factor when using equipment
-do it to meet performance criterions
-do periodically to ensure properly functioning equipment

can make comparisons to normative data collected within a clinic facility or in reference to existing external sources of data

-establish how to analyze waveform amp and latency
-draw diagrams to aid others
-need latency values for I, III, V, interwave latencies, amplitudes for I, V; V:I amp ratio

1. inflexibility in test protocol
2. few carefully defined and published normative databases for threshold ABRs, ECochG, MLR
3. For certain ABR applications, databases might be more appropriately obtained from patients who are not necessarily normal but who simply do not have the pathology of interest

time consuming, availability of normal subjects, must do norms over if you change a setting

-instrumentation
-subject characteristics
-stimulus parameters
-acquisition parameters

-limit to one page if possible
-include copies of actual ABR waveforms w/latencies marked and summarized in table

copies of ABR waveforms
test parameters
latency values

-occurs within 1st 2-3 msec after abrupt stimulus
-consists of 2 sound evoked cochlear potentials and compound 8th cranial nerve action potential

cochlear microphonic and summating potential

-alternating current potential that follows waveform of stimulus
-pure tone stimulus produces CM that appears like a sine wave of same frequency
-arises from OHCs
-best evoked by sinngle polarity stim, alternating will cancel it out

-direct current potential recorded following a continuous tone or a transient stim
-shift in baseline of recording, usually occurs in same direction or just prior to compound AP of 8th nerve
-precise source unknown
-clearing observed with extremely rapid stim and more prominent with high frequency tone burst stim

-far-field representation of compound AP of 8th cranial nerve
-also called N1
-same as ABR wave I
-reflects synchronous firing of 8th nerve fibers
-amp is largest for transient stim with abrupt and rapid rise times
-amp inc, latency decreases with stim intensity

larger amp with promontory electrode placement versus EAM

amplitude increases and latency decreases with stimulus increase

-range of 5-10 msec
-if you want to record only ECOchG, use 5 msec
-If you want ECochG and ABR, use 10-15 msec

typically use bandpass filter settings of 3 or 10 Hz to 1500 or 3000 Hz

-objective identification of Meniere's disease and endolymphatic hydrops
-enhancement of wave I and identification of I-V interwave interval
-monitoring of cochlear and auditory nerve function during surgical procedures that place ear at risk for permanent damage

ratio of 0.45 or greater is considered abnormal

brainstem glioma
-most often found in children and adolescents
-grow slowly and are highly invasive
-have ABR abnormalities

affect the myelin sheath of neurons, affecting axons of both CND and peripheral nervous system

most common demyelinating and major cause of neurologic impairment in adults
-more prevalent in colder climates

-prolonged interwave latencies
-decreased amp
-poor morphology
-poor repeatability
-total absence of components
-most characteristic: increased wave V latency

-progresisve childhood disease
-considered childhood MS
-deafness, blindess, death in 1-5 years

70% found in supratentrial compartment of brain

70% found in infratentorial (within posterior fossa) for children

schwannomas
neurofibromas
menigiomas

glioma
meningioma

most common 8th nerve tumor
grow slowly
hearing loss is common complaint

NF1 and NF2
NF! more common
tumors arise from Schwann cells
see hearing loss in over 90%

if it involved 8th nerve, difficult to distinguish from schwanoma
-ABRs abnormal
-found in various intracranial regions

1. when doing contralateral, make sure you dont have bilateral tumors, or serious hearing impairment in other ear
2. abr recordings from contralateral ear may provide diagnostically useful info on tumor size and functional effects

1. normal wave I-III, prolonged III-V
2. abnormal wave I-III and normal wave III-V
3. no detectable wave V with either normal or abnormal wave I-III latency interval

click=normal ABR and LI functions

wave V latency increases as HL at 4kHz increases

steeper than normal LI function, see minimal latency increase in wave V at high stim intensity levels

wave I disappears because only more apical regions of cochlea are activated

usually dont see ABR

wave V LI is steeper than normal, wont see wave V at low intensity levels

increase in absolute latency of I, III, V

latency of V prolonged at all intensities
-Wavw V LI may be same as conductive

-AP latency decreases slightly and amp increases as stim intensity increases
-SP not seen at lower intenisty levels
-CM only present with mono-phasic stim polarity
-increase stim rate will eventually reduce AP amp vs SP will remain the same
-morphology changes dramatically with click vs tone and also for low freq vs high frequency tone bursts

largest amp with click at high intensity

should use ABR first because it is inexpensive, readily available, noninvasive, office procedure with proven high sensitivity and may reflect small lesions not visible with CT

determine presence and location of wave I by comparison to contra recording
-obtain better definition of waves IV and V because they tend to be more separate in contra recordings

1. compression or stretching of the 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 and cochlea

need to eliminate electromagnetic artifact by using shielded earphone

better suited for AEP measures, especially for high frequency or click stimulus
-frequency response in 1-4kHz is more uniform

must be aware of travel time=0.9
-less stim artifact beacuse transducer is away from electrodes
-less ringing
-less collapsed canals
-reduces possible cross over of stim
-reduces ambient noise

-be aware of occlusion effect
-restricted intensity range-only about 55 dB
-best in newborns

1. tone ABR thresholds are not similar to behavioral thresholds
2. ABR to 500 hz are poor indicators of low freq behavioral thresholds
3. waveform identification of ABR to 500 hz is difficult

-sum of rise, plateau, fall
-ex. 2-1-2
-times change with frequency

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

25 ms needed to incorporate increased latencies seen with decreasing stim intensty, HL, brainstem and infant pathology

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

-consists primarily of V and negativity V
-typically dont see I-IV at low-mod intensities or high intensities

-low freq tones are later than those in responses to higher frequency tones presented at the same intensities
-reflects cochlear travel time

-notched noise masking
-reccomened for infants b/c you dont know hearing loss, but only essential for testing when patients have steep losses
-one-octave wide notch centered on nominal frequency of the stim

-use to determine conductive hearing loss
-expected down to 20 dbnHL for 500 Hz and 30 dBnHL for 2000 Hz

ability to identify negative results show that the person does not have the disease

ability to identify positive results

-stacked ABR wave V amplitude is more sensitive than standard ABR wave V amplitude measures to a small reduction in or desynchronization of auditory neural activity that may result from compression by a small tumor
-

-babies can fail screenings because of temporary conductive loss-bone ABR could be better
-latencies can change as structures mature
-wave I stays the same-shows cochlea matures

Click abr compared to behavioral thresholds
-best at 2000 Hz, worst at 8000Hz
-LI function related to slope of loss but was very variable

-with 8th nerve tumors, I-III usually abnormal, but III-V can also be normal
-ABR interwave measurement has better specificity than sensitivity

ABR to tones in notched-noise technique gave accurate estimates of pure-tone behavioral sensitivity for all frequencies