1. Auditory Evoked Potential (AEP)Testing
Lecture 11

2. Outline Principles/Background Purpose/Features View video
Clinical application/limitations
ABR Interpretations
Threshold
Differential Diagnosis
Other Evoked Potentials

3. Underlying Principles
Normal auditory system
Transmit acoustic stimuli into an electrical response
Stimulus – triggers “Action Potentials”
Response to the stimulus is extremely small
Repeated stimuli –response patterns “averaged” over time result in a robust tracing that’s observed

5. Background
Computerized test of hearing (cochlear) and auditory nerve (neurological) functioning
Used in evaluation of:
Hearing Integrity
Neurologic Integrity
First application 1971(Jewett and Williston)
Hundreds of published clinical studies on applications
Does not provide info about cortical areas

6. Purpose
To convert acoustic stimuli into electrical stimuli and measure associated brain wave activity
Brain wave activity is monitored by measuring computer-averaged changes in EEG activity
Electrical responses recorded from the scalp in response to an auditory stimulus
Time that it takes for sounds to travel can be measured on the acquired waveforms

7. Features Objective test Noninvasive Ear specific
BAER. BSER, BAEP,ABR
Noninvasive
Ear specific
Performed in quiet or sleep state
Performed with AC and/or BC
Performed with frequency specific stimuli

8. Clinical Application of evoked potential testing
Differential diagnosis (cochlear and retrocochlear)
Screening procedure for newborns
Diagnostic tool to ID HL in infants and children
Estimate hearing in difficult to test population
Intra-operative monitoring
Prognostic indicator with head trauma

10. Generator sites of ABR
Major peaks in waveforms: labeled by Roman numerals I-V
Response originates in the VIIIth cranial nerve
Wave I: VIII distal
Wave II: CN
Wave III: SOC
Wave IV: LL
Wave V: IC

11. Generator Sites
Without exception, every anatomical structure on one side of the brain has an identical structure on the opposite side.

12. Synchronous activation
Reflects synchronous activation
(onset type neurons)

13. Synchronous activation

14. Frequency range of ABR response
Response dependent
on activation of basilar
region of the cochlea in
response to click (2K-4K)

15. Stimulus
Click: brief duration signal, broad band signal ______through AC headphones
Tone burst : provides more frequency specific info
Rate of stimulus: _______/sec
Intensity : Start w high intensity and decrease Lowest level at which a repeatable waveform observed (of wave _______) is called threshold

16. Preparation Application of recording electrodes Placement of earphones
Vertex
Forehead
Earlobe/mastoid
Placement of earphones
Patient lying still or asleep
30 minutes or longer

17. Electrode Set up

19. ABR clinical measures (time)
Two Metrics
Inter-wave Interval
Absolute latency value
of wave

20. ABR clinical Measures (intensity)
One Metric
Absolute threshold

21. Factors that influence ABR
Age of subject (<18 mos., >60 yrs)
Longer latency values for older and younger clients
Gender
Not affected by most drugs (including sedatives)
Movement
Temperature

22. Clinical limitations
Frequency range Hz, most important to ABR
Does not estimate hearing levels in lower frequency ranges
ABR is NOT a test of hearing
Response provides no information on the auditory system above the brainstem level

23. ABR mostly reflects higher freq hearing

24. Normal Hearing: Wave V threshold @ 20 dB: Suggests normal hearing
I-V interval

25. ABR used to determine cochlear function
II III IV V
Lower intensity associated with increased latency values
Try to ID the dB HL level where you still observe Wave V V V V

26. Threshold ABR - Moderate HL
Wave V responses observed down to 55 dB HL
Results suggest a possible moderate hearing loss

27. Threshold ABR: Severe HL
What is threshold?

28. ABR to determine function of VIIIth nerve
Multiple Sclerosis
VIII nerve tumors
Meniere’s Disease
Auditory Neuropathy
Calculate Interwave Interval

29. Calculate IWI Hearing: WNL Right sided tinnitus
Intolerance to loud sounds

30. Acoustic Neuroma

31. Reporting results of ABR

32. What would ABR look like?

33. Differential Diagnosis

34. Examples of Differential Diagnosis

35. Screening ABR Prevalence of HL NICU: .5-5% Well baby <1%
Conducted on newborns prior to discharge
Test at 2 levels: 60 dB HL and 30 dB HL
Factors influencing outcome:
Neurologic abnormalities
Poor health
Transient conductive problems
Muscle artifact
Collapsing canals
Earphone placement

36. Screening ABR
60 dB HL
30 dB HL

37. Cochlear Microphonic (CM) (Wever and Bray, 1930)
Summary of classic research
Electrode in the auditory nerve of a cat
Speech through loudspeaker
The resulting electrical activity when transduced back to sound (thru a telephone receiver) and amplified, was transmitted as clear speech
Pure tones were reproduced accurately as well up to 3000 Hz.

39. CM defined
An electrical response from the cochlea reflects a combination of IHC and OHC function in response to acoustic stimulation
CM Mimics the form of the sound pressure waves that arrive at the ear … (aka a “stimulus following response”
Reverses in phase with changes in the stimulus polarity from rarefaction (-)to condensation (+)(Ferraro & Krishnan, 1997).
looks like the waves "flip" or invert

40. Cochlear Microphonic in AN
AN is defined as absent or severely distorted ABR with preserved OAE’s and cochlear microphonics
CM “reverses or flips” when the stimulus reverses polarity (from + to -)
Can only be seen if ABR done with both + and – polarity

41. Other Auditory Evoked Responses
Middle Latency Response (MLR)
Auditory Late Response (ALR)

42. MLR Documentation of CNS dysfunction above brainstem through thalamus
estimation of auditory sensitivity in older children / adults (malingerers)
State of arousal

43. ALR Assesses higher cortical processing from A1 and A2 areas
P300 – information processing
Latencies slow with age
Auditory processing

44. Calculate Interwave intervals