Week 8: AMLR Flashcards
what is the wave sequence of an AMLR waveform
- Na, Pa
* then Nb, Pb
Po waveform on AMLR
- a small positive wave before Pa
- –is thought by some to not be a true component of AMLR
- –maybe its pam?
the Pa waveform on AMLR
*a positive peak at about 30 ms after click stimulus
PAM and AMLR
- pam occurs within the same frequency region as AMLR
- –myogenic potentials 10-20 ms
- –can distort the AMLR in the 12-25 ms region (Na and Pa)
- –PAM can be mistaken for AMLR
- –can also distort ABR recordings
- need to relax neck and use lower stimulus levels to avoid pam artifact
neural generators of AMLR
- subcortical/thalamic generators (complex generators)
- –Na= thalamic MGB and IC
- –Pa=the association cortex?
- the lack or knowledge of the generators precluded the use of AMLR as a response index for threshold audiometry
AMLR protocol
- stimulus: click (2-1-2 TB for threshold)
- rate: 7.1/sec or 17/sec
- –slower like 1 or 2/sec for younger pts
- polarity: alternating
- intensity: same as for ABR
- sweeps: 1000
- presentation: monaural AC
- transducer: inserts
- masking” 70 dB when indicated
- amplification: 75000
- sensitivity: 50 micro volts
- window: 10-50 up to 80/100 ms
- filters: bandpass 10-1500 Hz
- electrodes:
- –threshold: Fz, A1, A2, Fpz
- –neurodiagnostics: C5 and C6
AMLR electrode montage
- noninverting electrode
- –for threshold finding:
- —–Cz= large Pa amplitude
- —–Fz= large amplitude
- –for otoneurologic (looking for asymmetry)
- —–C3 or C5= L temproparital
- —–C4 or C6= R temproparietal
when to do AMLR with a click vs a toneburst?
- clicks for otoneurologic purposes
- TB for thresholds
- –dont generally use AMLR for thresholds because they mature later, but when mature responses will be between 5-10 dB of threshold
AMLR with increase in intensity
*not much of a latency shift, but an increase in amplitude with increased intensity
stimulus rate for adults with AMLR
- recommended rate is 17/second
- –using a 50ms analysis window, the max allowable rate is 20.s so a stable AMLR will be present up to 15-16/s
- fast rates (15-40Hz)
- –using 40/s gives 40 Hz response= steady-state response
- —–overlapped response
- —–this is a sine wave
stimulus rate for newborns for AMLR
- lower rate: 1-2/s
- rate>/= 5/s would mean no Pa wave in newborns
- –note that with infants Na is greater than Pa which is the opposite of what you see with adults
stimulus polarity with AMLR
alternating is the best
age effect on AMLR
- AMLR can be elicited at any age, but varies
- –Pa amplitude increases from infancy to childhood, then decreases with advancing age
- AMLR are not adult-like until 8-10 yrs or later
- –at 8-10 yrs still need to be interpreted with caution
- need age-related norms
AMLR in adults vs neonates and young children
- adults
- –Pa is valid and reliable
- –ipsi and conta recording while stimulating one ear with a moderate intensity gives clear AMLR to be recorded from both sides of the head
- neonates and young children
- –Na is the most reliable waveform
- —–Pa: using a slow rate and nonrestricive high-pass filter (30-100Hz)
- –only ipsi recording because contra takes longer for the pathway and generators to mature so it will be ugly
AMLR and attention and state of arousal in children
- no attention to the stimuli means Pa amplitude decreases
* sleep means reduced amplitude (40% reduction) but pa latency is stable
AMLR and attention and state of arousal in adults
- can be recorded during light sleep and mild sedation
- norms are needed for each stage of sleep
- –generally want them to be awake with eyes open so have them read a magazine or something
AMLR and body temperature
- hypothermia (42.2 degrees C)
- –Pa latency and amplitude decreases
- —–poor morphology
- high fever will make AMLR earlier with reduced magnitude, so if you see bad AMLR rule out high fever
AMLR and sedatives
- Pa is sensitive to barbiturate (low dose)
- –morphine doesnt affect as much as barbiturates
- neuromonitoring in the ICU
- –better to record ABR because ABR is not affected by sedatives
AMLR and smoking
- smoking causes an arousal effect on generators of the AMLR leading to a larger response
- —older smokers have better Pa, younger smokers have better Pb
- smoking actually enhances the response, increase of neurotransmitters from nicotine?
clinical applications of AMLR
- threshold estimation
- –nonorganic hearing loss
- BIC evaluation
- comatose cases
- neurologic disease
- CI user
- ANSD
benefits of AMLR for threshold estimation
*relatively easy and valid
AMLR for BIC evaluation
need to measure binaural and then compare the BIC to it (the bic is the sum of the monaural for the left and the monaural for the right)
AMLR for neurodiagnosis
- compare the c5 to c6
- –site of lesion will be where the magnitude is abnormally small ( i dont think the latency is affected by lesions for AMLR)
- will see ear effect on side of lesion ( every time you stimulate the ear with a lesion you will see a problem)
AMLR and auditory neuropathy
*clearly recorded AMLR with ABRs absent is in agreement with the diagnosis of auditory neuropathy
AMLR and CI
AMLRs should be able to be recorded in response to 8th nerve stimulation by the implant at intervals between power pulses to the implant. these power pulse artifacts are visible at the beginning and end of the trace
