1) Auditory Brain Stem Response (ABR) testing is used to assess the integrity of the auditory system from the eighth nerve through the brain stem. 2) ABR represents the synchronous neural activity in the auditory pathway from the first through sixth order neurons in response to click stimuli. 3) Several factors can affect ABR results including age, gender, temperature, medications, attention, hearing loss type and degree, stimulus variables like rate and intensity, and recording parameters.

1. Auditory Brain Stem Response
ABR testing is the most effective diagnostic tool to assess the integrity of the auditory system from
the eight nerve up through the level of the brain stem but result can be affected by conductive &
cochlear disorders as they affect the level of the stimulus activating the auditory pathway.
This tool is a representation of the synchronous discharge of onset sensitive activity of the 1st
through 6th order neurons in the auditory pathway.
The ABR is used for neonatal hearing screening
In estimating hearing thresholds in patients that cannot or will not comply with behavioural
measures.
Subjective variables
1) Age :The ABR is incomplete at birth. Only waves I,III ,V are observed.Absolute latency of
wave III & V are longer than those of adult rendering their interpeak latency values
(especially wave I-V) prolongd relative to adult values.
2) Gender: Female often have shorter latencies (.2ms ) & larger amplitudes (waveIV& V) than
male.
3) Temperature: Temperatures exceeding ±10C (Below 36 or abve 38c) may affect the latencies.
A correction factor of -.2ms for every degree of body temperature below normal& -.15ms
for each degree of body temperature above normal can be used for the wave I-V iner peak
latency.
4) Medication & drug :chronic alcoholic
5) Attention & state arousal: Muscular & movement artefact are unwanted noise in ABR.
Muscular Neck & jaw &movement artifacts are unwanted noise in an ABR assessment.It is
important to encourage a natural sleep-like state Or medically induce a drawsy or sleep
state.
6) Hearing loss : In conductive Or mixed hearinh loss ,substract the amount of the air-bone gap
from the signal level & compare results to norms for that level.
In cochlear impairments,low –frequency losses have negligible effect on the click ABR.
High frequency cochlear losses yield essentially normal-click ABR,provided the loss is no
more than moderate & the signal is 20db above the pure tone threshold at
4000Hz.Otherwise cochlear losses can degrade waveform morphology,alter latency &
decrease amplitude but not in a perfectly,predictable way.
When an ABR is abnormal, one must consider the type, degree , & configuration of hearing
loss before presuming retrocochlear involvement.

2. Stimulus Variables
1)Click polarity : in mot patients,rarefaction result in shoter latency ,higher amplitude for early
components, & a clearer separation of wave IV &V components than do condensation clicks.
2) Rate : Stimulus rates over 30clicks /sec begin to increase latency of all components.Fast click rates
greater than 55/sec tend to reduce the wave form clarity.Rates influences wave V the most & there
fore III-IV &I-V intervals.
3)Intensity : As the intensity increases, amplitude increases & latency decreases.
4) Stimulus frequency: Higher frequency stimuli result in shorter latencies than do lower frequency.
Such as 500Hz tone pip,because they emanate primarily from the more basal turn of the cochlea.It
requires more time for a signal to travel to the lower frequency region of the cochlea.
Recording parameters
1) Electrode montage : waves IV & V are better separated in contralateral recording, Wave I &
III are more prominent in ipsilateral recording.A horizontal montage (ear to ear as opposed
to vertex to ear ) results in an increase in wave I amplitude.
2) Filter setting : up to 3000Hz ,high frequency information results in increased amplitude &
decreased latency. Below 1500 Hz ,low frequency information results in rounded peaks &
longer latencies.