Week 5: Threshold ABR Flashcards
when to do evoked response audiometry
- when real audiometry doesn’t work
- is impractical
- or a medical-legal case
when to use ABR to rule in/out hearing loss
- neonates: ERA is more precise
- low functioning
- or setting: post PE tubes in the difficult to test pop
- hysterical/ medical-legal
when to use ABR to rule in/out conductive component with an AC and BC ABR
- abnormal immittance testing
- when AC-ABR cannot be justified with immittance testing
- physical abnormalities
stimulus parameters for threshold ABR
- stimulus: click or TB
- polarity: rarefaction
- intensity: depends
- presentation: monaural
- –can also do binaural till no response then monaural
- rate: (30/second or higher wont sacrifice quality
why use odd number rates
dont want numbers divisible by 60 to limit power line interference
repetition rate effects on infant ABR
- RR 9.5/second was 100% present responses
- RR of 59.5/second was 56% present responses
- all this to say, minimum change in morphology and latency until going over 60 clicks/second
do you need to mask threshold ABR
- most likely no
* generally use inserts and have high sound attenuation, masking might be needed for BC
threshold ABR protocol
*no standard protocol, broadly applicable parameters/methods bu circumstances will dictate
*long-duration stimuli are ideal to approximate behavioral thresholds
*higher rate are better for
Dx
*20/25ms window (the younger the subject the longer window needed because longer latency)
*start looking at big pic, aka stopping at 20-30 dB because close enough to normal, then reduce as time permits, same thing for number or freqs
*very important to have non-stimulus control run
criteria for resposne
- use clincial judgement for what is a response
- the lowest click intensity where wave 5 can be elicited
- –different from residual noise
criteria for threshold
- click ABR threshold correlates best with hearing sensitivity between 1-4 kHZ
- –note you should label and average after the child leaves, not while testing
factors that can influence click ABR
- a complex relationship between cochlear HL and ABR because of interaction between:
- –type of HL
- –degree and configuration of HL
- will affect the L-I function
wave V L-I function for cochlear HL
- wave V latency increases as a function of the degreee of loss at 4 kHz
- correcting wave V latency is important for neurodiagnosis
- –subtract 0.1 ms/10 dB of loss above 50 dB at 4kHz
- high frequency HL will affect earlier waves because they are already small and will get smaller
central conduction time
interpeak latency between wave I-V
*gives info about the transmission of the signal through the brain
L-I function for CHL
*with conductive HL need to correct the latency to see if the brainstem is okay, to do this subtract 0.1ms from latencies for every 10 dB of CHL
limitations to predicting the type of HL from L-I function
- individual variability with different degrees and slope of loss
- small intensity increments (10 dB) are necessary to describe the slope of funciton
why do you have to take into account peripheral HL when using ABR
- to avoid interpreting results (and effects of CHL or SNHL) as a retrocochlear lesion
- –need to take into accound the effect of the peripheral HL and correct for it
correction factors for SNHL
*correction of 0.2 ms to wave V for every 10 dV of threshold increase above 50 dB at 4000Hz
correction factors for CHL
correction of 0.3ms/10 dB ABG for waves I, V, at 60 dB nHL simulus
are click ABRs sensitive to low frequency HL?
no because most energy around 2-4K
*in other words, ABRs can miss low-mid frequency HL
estimation of PTA from click ABR via derived response
- high pass masking noise with a high low-pass cut-off at 4, 2, 1, and 0.5 kHz
- gold standard for freq specific ABR testing (is only in research currently, not clinical)
- will expect response latency to be longer with lower frequencies because of travel time.
- –the latency shift rules out hydrops
- this is the basis of stacked ABR
estimation of the PTA from click ABR via notch-band noise procedure
- a notched noise masking paradigm to establish cochlear regions contributing to the response
- notch band noise will create a frequency specific response around the frequency the notch is centered around.
- morphology will not look like that of a click.
- latency of wave 5 will not be similar to that of a click because it will be later for lower frequency notches because it will take longer to see the response coming back because the stimulus will take longer to get where it is going
estimation of the PTA from click ABR with MLS
- MLS is maximum length sequence
- fast signal repetition rate with several responses to occur within the analysis window
- but little to no advantage of MLS over standard (slow averaging)
- may be helpful in APD
- deconvolved is averaging all responses in the single recording window
- –i think this uses a really fast rate
SN10 for different approaches to ERA
- SN10 is the slow deflection that peaks at or beyond 10ms following the stimulus onset
- is the trailing edge of wave V of the ABR or part of Na of AMLR
- use a window of 20 ms
- filter set to 40-3000Hz
- used to identify wave V
- basically this is especially good for 500 Hz TB when waves are pot pretty so the trough will be easier to see than the peak of wave V, especially near threshold
what type of envelope you use for toneburst
blackman, but no difference between linear gated 2-1-2 and blackman gated toneburst
should you use a wider or narrower bandpass filter for TB ABR and threshold seeking click ABR in infance
*for threshold testing want to use 30-3000 filter for the click ABR response to get a high resolution of the ABR and a well-defined response because there is more high and low frequency in the bandpass. However to be able to see wave 5 when threshold testing with a bandpass filter of 150-3000 can look at the trough to find the threshold if the subject is too noisy to use 30-3000
in what frequencies are the correlations between ABR and behavioral thresholds closer
much better correlation between higher frequencies than lower (note there is a bigger correction factor for low frequencies)
validity of ERA thresholds
- comparing to behavioral thresholds is like comparing apples to oranges as there is a different stimuli, the shorter stimuli with ERA leads to higher thresholds
- most valid comparison likely for
- –normal
- –conductive
- —sensory losses
- —–still comparison is difficult in cases of sharply sloping HL
- hard to predict for cases of neural/central environement as behavioral is a cortical response to puretones and ABR is a brainstem response to TB
frequency following response (FFR) for ERA
- remains of research interest
- note these are not CM
- this is the bases of ASSR and is looking at the softest sound where you no longer see the response
40 Hz ASSR for ERA
- evoked by repeated stimulus at 40/s
- provide excellent responses with very low frequency stimuli
- more objectivity identified– re AMLR
- more vulnerable to sleep
- is the basis of ASSR with high modulation rate
AMLR as an approach for ERA
you want to be awake for AMRL
*looks at Na which is the negative peak and Pa which is the positive peak. The 500 Hz tb is much nicer than the 4000 Hz for this test so it is a threshold finding option for someone who can stay awake if you cant get a nice 500 Hz ABR from them
ALR for ERA testing
want pt to be alert for ALR testing
- N1-P2 complex (slow cortical potential)
- best AEP for pseudohypausis
- looks at the N1 and P2 and tends to have a nice response becuase it is a cortical response
bone conduction AEP
- stimuli is click or low frequency TB
- fundamentally not different from AC testing expect output is limited to 50 dB HL due to transducer
- lower intensity can show a better response because less electrical interference/distortions in the bone oscillator
ABR parameters for air vs bone conduction testing
- same filter: 30-3000
- same stimulus: clicks or TB
- polarity: rarefaction for AC and alternating for Bone
- Rate: 9.3/39.7 for AC, 7.1-29.7 for BC
- more: ipsi and contra for both
- basically same montage for both but can use earlobe placements for BC
ipsi vs contra recordings for bone conduction
ipsi is actually better than contra for BC close to threshold and low tones are also better for bone conduction
general ABR strategy for infants and difficult to test children
*apply electrodes
—verify the impedance and keep the interelectrode impedance under 2 k ohms
*start with a 60 dB nHL unless prior info makes a severe loss likely
*replicate at each level for AC
*if response is present
go 20-30 down and 10 dB up
*if elevated response levels and CHL suspected the do BC ABR and plot the L-I function
*if elevated response levels and SNHL suspected then do frequency specific testing
*then test the other ear
what 6 things should the ABR report include?
1) summary of the clinical history
2) objectives of the test
3) type of AEPs recorded
4) relevant medications
5) description of waveforms, amplitude, latency at high level and clinical importance of any AEPs abnormalities
6) report ABR thresholds (dB nHL) and estimated thresholds (eHL in dB HL)
clinical principles and caveats on hearing evaluation with AEPs
- no single auditory measure adequately evaluated all aspects of hearing
- no diagnostic procedure is prefect
- AEPs should be supplemented with: PTA, speech audiometry, immittance, and OAEs
