Week 8: AMLR Flashcards
1
Q
what is the wave sequence of an AMLR waveform
A
- Na, Pa
* then Nb, Pb
2
Q
Po waveform on AMLR
A
- a small positive wave before Pa
- –is thought by some to not be a true component of AMLR
- –maybe its pam?
3
Q
the Pa waveform on AMLR
A
*a positive peak at about 30 ms after click stimulus
4
Q
PAM and AMLR
A
- 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
5
Q
neural generators of AMLR
A
- 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
6
Q
AMLR protocol
A
- 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
7
Q
AMLR electrode montage
A
- 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
8
Q
when to do AMLR with a click vs a toneburst?
A
- 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
9
Q
AMLR with increase in intensity
A
*not much of a latency shift, but an increase in amplitude with increased intensity
10
Q
stimulus rate for adults with AMLR
A
- 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
11
Q
stimulus rate for newborns for AMLR
A
- 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
12
Q
stimulus polarity with AMLR
A
alternating is the best
13
Q
age effect on AMLR
A
- 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
14
Q
AMLR in adults vs neonates and young children
A
- 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
15
Q
AMLR and attention and state of arousal in children
A
- no attention to the stimuli means Pa amplitude decreases
* sleep means reduced amplitude (40% reduction) but pa latency is stable
