Lecture 5

Question 1

When was the first ABR recorded in infants?

Answer 1

1974

Question 2

Why are ABRs most useful in infants?

Answer 2

Because behavioural audiometry is not possible so we need an objective measure

Question 3

What is the estimate of prevalence of infant hearing loss? At what dB HL?

Answer 3

1/1000 at 40 dB HL or greater

Question 4

What are the main principles from the joint committee on infant hearing (2007)?

Answer 4

-All infants should be screened within 1 month
-Full audiologic/medical evaluation by 3 months
-All infants with HL should have intervention by 6 months

Question 5

What 2 kinds of OAEs are used to screen healthy babies?

Answer 5

TEOAE & DPOAE

Question 6

What is the automated auditory brainstem response used for (AABR)?

Answer 6

-AABRs are used for screening in NICU
-Assesses more of the auditory system compared to OAEs

Question 7

What are the 3 possible categories of results for ABR?

Answer 7

1. Response (hearing)
2. No response (not hearing)
3. Noisy result (inconclusive)

Question 8

Which wave is most important in an ABR?

Answer 8

Wave V because it’s big enough to give you thresholds

Question 9

Electrode placement locations: active, reference, and ground

Answer 9

-Active (non-inverting) at vertex (Cz) or forehead (FPz)
-Reference (inverting) at mastoid (TP7 or TP8)
-Ground on lower forehead / contralateral mastoid / clavicle

Question 10

Target impedance for babies

Answer 10

< 10 kOhms and within 1 kOhm between electrodes, but higher absolute impedances may be warranted

Question 11

For threshold ABR, why is the low-pass filter generally 1500 Hz?

Answer 11

Since we’re doing threshold ABR instead of neurodiagnostic ABR, the exact latencies aren’t important, so we care more about having a smoother result

Question 12

For threshold ABR, why is high-pass generally 20-30 Hz?

Answer 12

To get a stronger wave V

Question 13

Weighted Averaging

Answer 13

Weighted averaging ensures that very noisy sweeps are not included by setting a rejection level (this is preferred over non-weighted averaging which averages all responses)

Question 14

What correlation value is strongly suggestive of a response?

Answer 14

.46 or greater

Question 15

T/F: we can measure evoked potential (EPrms) on its own

Answer 15

FALSE: always measuring evoked potential + background noise

Question 16

How do you estimate SNR?

Answer 16

-Estimate amplitude of background noise
-Divide response amplitude (which includes noise) by this
-Subtract 1

Question 17

What are the 3 basic methods of estimating background noise?

Answer 17

-Signal absent recording (e.g., a pre-stimulus baseline)
-The plus/minus average
-Trial-to-trial variance

Question 18

Estimating BN: Signal Absent Methods

Answer 18

-Compare amplitude of trial with stimulus present (EP + BN) with amplitude of trial with no stimulus present (BN)
-This requires two runs, one with stimulus and one without
-Problem: the brain changes after stimulation (even the noise isn’t the same) —> induced activity

Question 19

Estimating BN: the plus/minus average

Answer 19

-Create an estimate of the noise, by inverting every other response before averaging
-Anything consistent from trial to trial should get subtracted away (e.g., you average a positive wave V and a negative wave V)
-Advantage to this approach is that the background noise is obtained from the same time period as the response, so the normal equation holds

Question 20

Estimating BN: Trial-Trial Variance

Answer 20

-Basic approach:
·Pick a single time point (e.g., wave V peak)
·Record response amplitude at this time point over individual trials
·Find the difference between each trial amplitude and the across-trial amplitude
·Since these differences will be positive or negative, the average difference will be zero, so we square them to make them positive
·The sum of the squared values (SS) divided by the number of trials is the mean squared value (this is variance or power of the noise)
·The square root of the mean squared value is the standard deviation (this is the background noise amplitude)

Question 21

What is residual noise also known as?

Answer 21

Background noise estimate

Question 22

What is the best approach for estimating background noise?

Answer 22

The trial-trial variance because although it is similar to the plus/minus average, it uses actual trial-trial differences instead of just average differences (where some of the noise gets averaged away)

Question 23

T/F: signal-to-noise ratio is a ratio of amplitudes and if you square it, you get a ratio of powers

Answer 23

TRUE: SNR^2 is a ratio of powers, and therefore is an F statistic

Question 24

What is Fsp?

Answer 24

When the noise is estimated using trial-to-trial variance, measured at a single time point. Fsp = F single point

Question 25

What Fsp value gives you a 99% confidence interval?

Answer 25

3.1

Question 26

What is Fmp?

Answer 26

F multiple points (most clinical systems include this)

Question 27

The RN should be ~ ___ nV before deciding that no response is present

Answer 27

20

Question 28

Subjective vs. Objective methods to determine when you have enough averages

Answer 28

-Subjective: when response can be seen, ·Replicate to visualize variability (better: calculate cross-correlation) ·Run at multiple levels to visualize latency-intensity function -Objective: when response is sufficiently large relative to background noise (e.g., SNR > 1.2, Fsp > 3.1): BN can be estimated by baseline, +/- averaging or trial-trial variance or amplitude (but baseline is a poor choice) ·OR when background noise is sufficiently low (20 nV), even if no response

Question 29

__ dB nHL is the level most commonly used in ABR screening

Answer 29

35

Question 30

Automated vs. Non-Automated ABR Screening

Answer 30

-Automated: must use an objective criterion -Non-Automated: usually uses an objective criterion (SNR, Fsp, residual noise)

Question 31

ABR is the most accurate test of hearing for infants < ____ months

Answer 31

6

Question 32

What is the ABR stopping criteria?

Answer 32

-70 dB nHL stimulus —> stop when response observed -30 & 50 dB nH stimuli —> stop if one of the following: ·Fsp criterion reached AND at least 768 sweeps AND observed ·Low residual noise (<15 nV) was reached without response ·Maximum number of sweeps (6144) without response

Question 33

What peaks are visible in infant ABR and when do they mature to adult-like?

Answer 33

-Wave I: adult-like by 3 months -Wave III: adult-like by 8-16 months -Wave V: adult-like by 18-36 months

Question 34

Latency change with age

Answer 34

-Wave I settles first while wave V settles last

Question 35

Threshold is not affected by rates up to ___ Hz. Usually we use a rate of ___ /sec

Answer 35

50; 40

Question 36

T/F: stimulus phase (condensation or rarefaction) affects thresholds

Answer 36

FALSE: stimulus phase does NOT affect thresholds. We use alternating polarity to eliminate cochlear microphonic OR combine rarefaction and condensation after recording

Question 37

Procedural Considerations for Babies

Answer 37

-Newborn babies naps are short (roughly an hour at a time) ·Sedation with chloral hydrate when necessary (usually not required though with newborns) -Prepare baby before feeding ·Make sure the baby is not fed the hour before the appointment (want a hungry and tired baby!) -Begin testing at lower level (30 dB) ·Less chance of waking baby ·Less wasted time

Question 38

Procedural Considerations: Frequency & dB nHL

Answer 38

-Start with 2000 Hz at 30 dB nHL, then 60 dB nHL -If no response, try bone conduction at 30 dB nHL -Then find threshold in 10 dB steps -Get 2000 Hz in both ears first (and maybe 4000 Hz) before going on to 500 Hz, which is more difficult

Question 39

T/F: masking is generally not required for ABR

Answer 39

TRUE: if the other ear is responding, the response will be larger contralaterally. True for bone conduction in infants (10-15 dB IA for bone)

Question 40

What are the normal infant physiologic thresholds? (At 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz)

Answer 40

-500 Hz: 42-53 dB -1000 Hz: 37-38 dB -2000 Hz: 31-38 dB -4000 Hz: 31-43 dB

Question 41

How is estimated behavioural threshold expressed?

Answer 41

eHL

Question 42

How are ABR thresholds typically expressed?

Answer 42

dB nHL

Question 43

ABR threshold estimates have standard deviations that range from about __ dB to __ dB across various studies

Answer 43

5, 15