Estimating Hearing Sensitivity with ABR Flashcards
Are ABRs a true test of hearing?
No
The information obtained can be useful in estimating hearing sensitivity - we are inferring hearing status based on this test
ABR and other evoked potentials test neural synchrony
The ability of the CNS to respond to external stimulation in a synchronous manner
This synchronous neural response results from the firing of a large group of neurons at the same time
When are ABRs especially useful?
When you need to know the sensitivity of each cochlea separately
To compare responses by air conduction and bone conduction with or without masking and to estimate auditory function in frequency-specific ranges
Where are the max energy peaks for supra-aural headphones and inserts?
Between 1000 and 4000 Hz
Can we still use clicks while estimating hearing sensitivity?
No, because it is a broadband stimulus and doesn’t give a lot of specific information
Although pure tones are very hard responses to record (it won’t register as big of a response)
What are the different types of stimuli that have been proposed to provide information for narrower frequency regions of the cochlea?
Filtered clicks (remove some of the stimulus energy)
Clicks with high-pass noise (introduce noise to make a signal more audible; put noise around the signal to make it more apparent)
Tonebursts (generally used for threshold searches)
Tonebursts with high-pass noise
Tonebursts in notched noise
Amplitude modulated (AM) tones - ASSR
Frequency-modulated (FM) tones - ASSR
What stimuli do you use for a threshold estimated ABR?
Click (R/C) at 80 dB nHL - to rule out ANSD
Click threshold seek
Toneburst or chirp at high and low (4 kHz and 500 Hz)
What stimuli were found to maximize both frequency specificity and neural synchrony?
Toneburst with two cycles (or periods) of rise time
One cycle of plateau
Two cycles of decay
Do the onset and offset characteristics (envelope) of the stimulus affect the spectral energy or frequency characteristics of the stimulus?
Yes
A linear rise and fall of energy is characterized by an abrupt change from no stimulus to the rise of energy and a sharp change when the plateau is reached
If an envelope is used that has a more gradual onset and offset function, then there is less spectral spread of energy into other frequency regions (Blackman or Hanning)
It is more desirable to use this than a linear envelope to maintain as much frequency specificity as possible - with a tone burst
Is an ABR generated by a tone burst significantly different in appearance from those generated by a click?
Yes
Early waves (I and III) are not discernable
Wave V is still very robust and easily identified, especially at moderate-to-high stimulus intensity levels
Wave V still remains easy to identify even at lower intensity levels
Is wave V easy to identify with alternating?
Not always
It is not very easy to pick out at low intensity levels
It can, however, cancel out some of the noise
What is split buffering?
Breaking up the rarefaction and condensation from the single alternating run
Getting three waveforms out of one run - makes the process faster
Are higher frequency responses easier to see than low frequency?
Yes
More noise is present in lows and there are higher correction factors
Do polarity reversals cause latency shifts in the wave V peak?
Yes, especially in low frequency tone burst stimuli (250 and 500 Hz)
2000 and 3000 Hz tonebursts are not significantly altered by polarity reversals
Except for ruling out ANSD, just pick one polarity and stick with it
Can using alternating polarity for lower frequencies be detrimental to response quality?
Yes
What is generally the focus of using ABR for an estimation of hearing sensitivity?
Quantifying hearing sensitivity in the lower frequencies
However, the use of high-frequency tone bursts can also be useful in certain circumstances (ototoxic medication monitoring)
Is there generally consistency in the data collected across clinics when the data is using the same test parameters?
Yes
So it is possible to use published normative data with proper precautions
What is normative data based on?
Age of patient
Intensity of stimulus
Stimulus parameters
Is it recommended that clinicians acquire ABRs on 5 to 10 normal subject?
Yes, they collect their own normative data
When beginning to use ABRs or when changing to a new ABR test system
Not relying on someone else’s work and able to use the test parameters that you plan to use in your clinic
Compare to published norms but make sure the same parameters are being used for the published data
Is there an issue of where to place the cutoff of normative data?
Yes, either using 2 or 3 SDs
Determination of the cutoff value is basically a trade-off between the sensitivity and specificity of the ABR in correct identification of abnormalities
Using 2 SD with place more normal patients outside of the normal range 3 SD
The use of 3 SD will include more abnormal subjects in the normal range than the use of 2 SD
Are infant ABRs very different from adult ABRs?
Yes
ABR waveform is incomplete at birth
Generally, only three major components (Waves I, III and V) are observed
Wave I is often the biggest for infants whereas typically wave V for adults (earlier components mature faster - distal; neuromaturation)
Interwave latencies are initially prolonged and absolute latency is normal about 5 ms (instead of 4 ms) - the system is not as efficient yet, doesn’t conduct the signal quite as quickly
Morphology also isn’t that good
Do other wave components emerge during the first 18 months after birth?
Yes
Waves III and V progressively shorten in latency
After the first 18 months to 2 years, the ABR is essentially adult like in latency and amplitude
Age must be considered when interpreting ABR findings in children under the age of 18 months
What is conceptional age vs gestational age?
Conceptional age is calculated from calendar dates from the mother’s last menstrual cycle
Gestational age is determined from physical examination
Up to a 2-week margin is presumed
Need to consider this factor and adjust accordingly
How can you estimate hearing sensitivity through ABR?
Progressively decreasing the intensity of the stimulus (click and toneburst) until no response is discernable
Plotting the absolute latency of wave V on an age appropriate LIF form
What is evaluated with aid conduction clicks?
Higher frequencies
External ear, middle ear, cochlea, VIIIth nerve, and brainstem
