Lecture 4

Question 1

What 2 things can affect latency and amplitude?

Answer 1

1. Gender
2. Age

Question 2

Females show ____ latency values and ____ amplitudes than males for later ABR waves (III, IV, V & VI).

Answer 2

Shorter, larger

Question 3

Because the effect is negligible for wave I and more pronounced for later ABR waves, ____ are significantly shorter for females.

Answer 3

Interwave intervals

Question 4

Adults up to ____ - it is best to establish separate norms for males and females

Answer 4

60 years of age

Question 5

Gender and hearing loss

Answer 5

• Females show little wave V latency change with increasing hearing loss,
• Wave V latency in males increase ~0.1 ms for every 20 dB decrease in the effective click level (i.e., 20 dB drop in thresholds)

Question 6

Why does gender play a role?

Answer 6

The mechanism underlying the difference is obscure.
- Differences in hearing sensitivity
- Body temperature
- Head size and brain dimension
- Physiologic and biochemical properties
- LIKELY greater travelling wave velocity in females and at young ages (less cochlear latency)

Question 7

How does low body temperature affect ABR? Why?

Answer 7

• With a drop in body temperature an increase in ABR wave latency is expected
  
  • Hypothermia in low-birth-weight infants
  • Persons in coma secondary to severe brain injury
• This is due to delayed synaptic transmission and decreased axonal conduction velocity.

Question 8

____ temperature slows things down

Answer 8

Low

Question 9

____ temperature speeds things up

Answer 9

High

Question 10

Open heart surgery need body temperature between ____ degrees C

Answer 10

28-32

Question 10

How can temperature affect neuropathy patients?

Answer 10

Fever distorts and can eliminate ABR

Question 11

What happens to interwave latency (I-V) below 37 degrees C?

Answer 11

• Increases by 0.2 msec for every degree of body temperature below 37°C (hypothermia)
• Think of cold as slower

Question 12

What happens to interwave latency (I-V) above 37 degrees C?

Answer 12

• Decreases by 0.15 msec for each degree of temperature above 37°C (hyperthermia)
• Think of hot as faster

Question 13

Is ABR affected by state of arousal?

Answer 13

ABR results are not affected by natural sleep state. Even extremely reduced states of arousal, such as narcolepsy and coma have no serious effect on ABR latency or amplitude.

Question 14

Effects of drugs on ABR

Answer 14

ABR is generally resistant to sedatives (e.g., Chloral hydrate) and anesthetic agents (e.g., Nitrous oxide).

Question 15

Muscular artifact on ABR

Answer 15

ABR wave components can be completely obscured by excessive muscle artifact, often arising from neck or jaw muscles.

Question 16

What are 3 offline manipulations (things you do with your data in the end)

Answer 16

1. Summing repeated measures
2. Subtracting repeated measures
3. Smoothing

Question 17

How does summing repeated measures work?
- how much does it improve?

Answer 17

• Same as if you had recorded all trials together
• If you do two complete runs, have the same number of trials in each, and the subject state doesn’t change, summing will increase the signal-to-noise ratio by a factor of 1.414 (roughly 40% improvement)

Question 18

How does subtracting repeated measures work?

Answer 18

• Removes anything consistent in the response
• Estimate of background noise

Question 19

How does smoothing work?

Answer 19

• This is low-pass filtering
• Helpful when response is noisy
• On-line low-pass filter often limited to 1500 Hz to make result look cleaner

Question 20

What are 3 cons to summing responses to alternate polarity stimuli?

Answer 20

1. Reduces response quality (because each polarity response is a little different)
2. Does not improve SNR as much as summing same polarity
3. Noise reduction should be the same (as with single polarity summing)

Question 21

What are 2 pros to summing responses to alternate polarity stimuli?

Answer 21

1. Reduces cochlear microphonic (this can be visualized by comparing the two polarities separately before summing)
2. Reduces artifact

Question 22

What are 3 things that happen with subtracting responses to alternate polarity stimuli?

Answer 22

• Removes most of the response
• Preserves cochlear microphonic
  
  • The CM inverts with the stimulus
  • Minus a minus is a plus!
• Preserves artifact

Question 23

If they don’t ____, it’s not ____

Answer 23

Repeat, complete

Question 24

What do you do if you can’t repeat?

Answer 24

Try splitting single measurement into split-halves

Question 25

What if waves repeat but are messy (e.g. difficult to identify specific peak latencies)?

Answer 25

• Try summing repeated measures (a post-hoc way of increasing the number of averages)
• Increase averages if possible
• If RN is high, try to find source
  
  • Stressed patient, eyes open, neck tense
  • Unbraided electrode wire, fluorescent light, near wall plug, crossed wires, etc.

Question 26

What are 5 problems associated with wave I?
- how do you record
- what do you raise
- what can you use
- where can you record from
- what should you try

Answer 26

1. Record at slower rates
   
   • 10.1
   • 7.1
2. Raise high-pass filter (to 100 or 150 Hz)
3. Use ear canal electrode (e.g. a Tiptrode), or TM electrode
   
   • Boosts the amplitude of wave I
4. Record from earlobe
5. Try a different polarity (rarefaction or condensation)
   
   • Usually rarefaction is clearest, but this is not always the case!
   • Look at the individual polarity waves

Question 27

What are 5 things associated with wave V?
- where do you record
- what do you vary
- what do you look for
- what do you do if it is very late
- what do you lower

Answer 27

1. Record vertical montage (e.g. neck ref)
2. Vary level to see L-I function
3. Look for following negativity
4. If it seems very late, use contralateral masking (to make sure not from other side)
5. Lower high-pass filter (e.g. to 30 Hz)