What range of hearing does ABR test
- 250 Hz - 1000 Hz
What is the wave I site generator
Distal portion of the auditory pathway
What is the wave II site generator
Proximal end of the auditory nerve
What is the wave III site generator
Second order auditory neurons in the cochlear nuclei
What is the wave IV site generator
The superior olivary complex
What is the wave V site generator
Fibres of the lateral lemniscus as they enter into the inferior coliculus
What are the stimuli for ABR threshold testing
Clicks and tone bursts
Why are tone bursts better than clicks
Gives frequency specific results
Strengths of ABR (2)
- They are not affected by arousal
- Resistant to sedatives
- Tests between 250-1000 Hz
Weaknesses of ABR (5)
- Has a splatter effect and requires a filter
- Results can be obscured by muscle movement
- High level of variability
- ABR won’t detect the loss between 6-8 kHz
- Pass from ABR does not equal normal hearing
How do you interpret ABR results
ABR results are 10-15 dB above the behavioural threshold
How do you interpret ABR results (2)
- ABR results are 10-15 dB above the behavioural threshold
2. If inserts are used, subtract .08
What is ABR (2)
- An electrical potential generated by a transient stimulus which generates synchronous firing of auditory neurons.
- Its waves are measured by latency and amplitude.
When do ABR waves occur
Within 15 ms after stimulus onset (short latency)
How do you interpret latency (5)
- Repeatability is required, not repeatable if wave V latency is <0.2 ms
- Compare wave V latency between ears, abnormal if ILD >0.25 ms at 70 dBnHL
- Asymmetry in ABR but not PTA
- Interpeak latency (I-V) - abnormal if I-V interval peak .4.4 ms
What are the disadvantages of calculating interaural latency differences (2)
- Not applicable to patients with bilateral tumours
2. Not applicable when there’s poor morphology
Magnitude of the amplitude depends on… (2)
- Number of neural elements activated by the sound of stimulus
- Degree of sychronisation of neural activity
