Lecture 4 Flashcards
What 2 things can affect latency and amplitude?
- Gender
- Age
Females show ____ latency values and ____ amplitudes than males for later ABR waves (III, IV, V & VI).
Shorter, larger
Because the effect is negligible for wave I and more pronounced for later ABR waves, ____ are significantly shorter for females.
Interwave intervals
Adults up to ____ - it is best to establish separate norms for males and females
60 years of age
Gender and hearing loss
- 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)
Why does gender play a role?
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)
How does low body temperature affect ABR? Why?
- 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.
____ temperature slows things down
Low
____ temperature speeds things up
High
Open heart surgery need body temperature between ____ degrees C
28-32
How can temperature affect neuropathy patients?
Fever distorts and can eliminate ABR
What happens to interwave latency (I-V) below 37 degrees C?
- Increases by 0.2 msec for every degree of body temperature below 37°C (hypothermia)
- Think of cold as slower
What happens to interwave latency (I-V) above 37 degrees C?
- Decreases by 0.15 msec for each degree of temperature above 37°C (hyperthermia)
- Think of hot as faster
Is ABR affected by state of arousal?
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.
Effects of drugs on ABR
ABR is generally resistant to sedatives (e.g., Chloral hydrate) and anesthetic agents (e.g., Nitrous oxide).
Muscular artifact on ABR
ABR wave components can be completely obscured by excessive muscle artifact, often arising from neck or jaw muscles.
What are 3 offline manipulations (things you do with your data in the end)
- Summing repeated measures
- Subtracting repeated measures
- Smoothing
How does summing repeated measures work?
- how much does it improve?
- 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)
How does subtracting repeated measures work?
- Removes anything consistent in the response
- Estimate of background noise
How does smoothing work?
- 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
What are 3 cons to summing responses to alternate polarity stimuli?
- Reduces response quality (because each polarity response is a little different)
- Does not improve SNR as much as summing same polarity
- Noise reduction should be the same (as with single polarity summing)
What are 2 pros to summing responses to alternate polarity stimuli?
- Reduces cochlear microphonic (this can be visualized by comparing the two polarities separately before summing)
- Reduces artifact
What are 3 things that happen with subtracting responses to alternate polarity stimuli?
- Removes most of the response
- Preserves cochlear microphonic
- The CM inverts with the stimulus
- Minus a minus is a plus!
- Preserves artifact
If they don’t ____, it’s not ____
Repeat, complete
What do you do if you can’t repeat?
Try splitting single measurement into split-halves
What if waves repeat but are messy (e.g. difficult to identify specific peak latencies)?
- 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.
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
- Record at slower rates
- 10.1
- 7.1
- Raise high-pass filter (to 100 or 150 Hz)
- Use ear canal electrode (e.g. a Tiptrode), or TM electrode
- Boosts the amplitude of wave I
- Record from earlobe
- Try a different polarity (rarefaction or condensation)
- Usually rarefaction is clearest, but this is not always the case!
- Look at the individual polarity waves
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
- Record vertical montage (e.g. neck ref)
- Vary level to see L-I function
- Look for following negativity
- If it seems very late, use contralateral masking (to make sure not from other side)
- Lower high-pass filter (e.g. to 30 Hz)
