otometrics Madsen AccuScreen PRO, Руководство пользователя

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18 GN Otometrics A/S
Test Methods AccuScreen PRO User Manual
stem (ABRs) are particularly well suited for hearing tests in new-
borns, infants and children. Reasons for this include:
• The responses are not influenced by state, and can thus be
tested during sleep. This is the ideal state to test ABRs because
it minimises influence of potentials from muscular activity,
which could make a good measurement difficult.
• Many investigations have shown that the behavioural hearing
threshold correlates strongly with the response threshold of
the brainstem. In other words: If an ABR can be tested as a
response to an acoustic stimulus, it is nearly certain that the
individual can hear this stimulus. It would only be in rare
cases of damage to the midbrain or auditory cortex that this
would not hold true.
Care must be taken during testing and evaluation in order to avoid
false results. The amplitude of the electric response to a 30 or 40 dB
stimulus is frequently below 100 nV and therefore considerably low-
er than the scalp electroencephalogram (EEG) and electromyogram
(EMG).
2.2.1 How the AccuScreen PRO A-module determines a PASS
Applies to AccuScreen PRO A, TA, DA, TDA.
The Auditory Brainstem Response (ABR) is a low-amplitude signal
usually buried in the electric brain and muscle activity (EEG and
EMG). It can only be extracted by applying special filtering tech-
niques. "Averaging" is the procedure most commonly used to make
it visible: the stimulus is presented repeatedly - up to several thou-
sand times - and the signal from the electrodes, which follow the
stimulus, is summed continuously until the response can be detect-
ed.
Visual detection and interpretation of such a signal requires a great
deal of expertise. For screening purposes, the decision to pass or re-
fer must be performed quickly and automatically. As a consequence,
a different evaluation approach must be used for screening.
Like the methods for automatic detection of TEOAE and DPOAE in
the AccuScreen PRO, a statistical approach determines the ABR
PASS criterion. The basic procedure - application of binomial statis-
tics - is the same as described in Section 2.1.4, ‘How the AccuScreen
PRO T-module determines a PASS” on page 15 . Because the shape of
the ABR response waveform changes with age, the detection algo-
rithm is optimised accordingly by pre-filtering the recorded signals
with a typical pattern for infants up to one year old. Although this
does not preclude testing older children and adults with the Accu-
Screen PRO, the sub-optimal fit may result in longer test times for
these patients.