Midterm Flashcards by Sabrina Garza

Latency-Intensity Function (LIF)

Relationship between intensity,latency & amplitude
* Intensity ↑ Latency ↓ & Amplitude ↑
* Intensity ↓ Latency ↑ & Amplitude ↓
* Plotting the absolute latencies of Wave V as a function of intensity yields a Latency-Intensity Function (LIF)

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What type of Loss?

Conductive HL
* Equally Prolonged (later) absolute latencies of all Waves.

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What type of loss?

Cochlear
* Cochlear Hearing Losses often show a steeper than normal LIF with
normal latencies at higher intensities and prolonged latencies at lower intensities.

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What type of loss

Retrocochlear
* Wave V latency prolongation
could also be Conductive - they look the same on LIF

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How can you tell the differnce between a coductive and a retrocochlear LIF?

You cant with just the LIF, you would be able to only tell a differnce by comparing the latencies of earlier peaks of the ABR.

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This ABR is often used in neurological testing for differential diagnosis

Rate Study ABR or Neurologic ABR

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What is a Rate Study ABR helpful with?

Is often used in neurological testing for differential diagnosis
* assisit in presence or absence of a disorder.(to a limited extent)
* Site of disorder (cochlear or retro)

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Rate Study ABR may also be helpful in identification of __ ___ such as those associated with multiple sclerosis and disorders that are not associated with a radiologically identifiable lesion, such as auditory neuropathy.

The ABR may also be helpful in identification of diffuse lesions such as those associated with multiple sclerosis and disorders that are not associated with a radiologically identifiable lesion, such as auditory neuropathy.

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Who should have a rate study ABR?

PT’s who report or present with …
* unexplained unilateral or asymmetric SNHL
* abnormally poor word recognition in quiet
* reduced word recognition in noise
* PIPB rollover
* sudden hearing loss
* Asymmetric HL
* Progressive HL
* Tinnitus or dizziness w/no HL
* Unexplained elevation or absence of MEMR
* PT’s who can’t do MRI

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Rate ABR Test protcol

Click Stimulus
70 - 90 dbnHL each ear
Inital rates ≈ 10 to 30 stimuli per second (baseline info)
Rates 11.1 or 27.7 stimuli per second are used to avoid repetition rates that are multiples of 60 Hz
When clear responses no longer obtained decrase rate to below 10 (7.7/sec)
If clear responses are not obtained at the initial test stimulus intensity, then the intensity may be increased to further define responses.
faster rate = prolongation of Wave 5 latency and reduced amp of wave 1&3

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Methods used to increase apparent Wave I amplitude include:

increasing the intensity of the stimulus
decreasing the presentation rate
comparing rarefaction and condensation clicks to distinguish cochlear potentials from neural responses
using a TM electrode in ECochG
using transtympanic ECochG
using a horizontal recording montage (A1 – A2)

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The ABR is sensitive to neurological disorders of the ___ and __ brainstem.
These disorders include …

The ABR is sensitive to neurological disorders of the VIIIth N and low- to mid-brainstem.
These disorders include
* space-occupying lesions
* diffuse lesions
* functional (physiological) abnormalities.

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what are the diagnosing limits of Rate study ABR?

The ABR is not sensitive to all central nervous system disorders.
* The ABR does not evaluate the integrity of the CNS rostral to (above) the brainstem, so cortical deafness can not be ruled out on the basis of a normal ABR.

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True or False

Rate study ABRs are sensitive to all CNS disorders?

FALSE
The ABR is not sensitive to all central nervous system disorders.
The ABR does not evaluate the integrity of the CNS rostral to (above) the brainstem, so cortical deafness can not be ruled out on the basis of a normal ABR.

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True or False

Threshold ABR is not a hearing test

TRUE
ABR is not a hearing test
* However, the information obtained can be very useful in estimating hearing sensitivity.

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What waves are most prominate in teh ABR for an infant and an adult?

Wave I often biggest for infants whereas typically wave V for adults

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Estimate Hearing Sensitivity
Can be obtained from ABR data by:

Progressively decreasing the intensity of the stimulus (click and toneburst) until no response is discernable, then
Plotting the absolute latency of Wave V on an age appropriate LIF form

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When to use ABR for Estimating Hearing Sensitivity

When you need a:
safe,
non-invasive approach,
to assess auditory function in
infants, children and adults
especially those who cannot participate in voluntary behavioral audiometry.

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what is the Three Part Protocol for Estimation of Hearing Sensitivity in Infants and Young Children

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ABR to AC Clicks
ABR to 500 hz Tone Burts
ABR to BC Clicks

ABR Can be useful for:

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Can be useful for:
* Identifying space occupying lesions or retro-cochlear disease
* Degenerative diseases (MS)
* Auditory Neuropathy Diagnosis (ANSD)
* Estimating Hearing Sensitivity

why might you perform a threshold ABR

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Newborn hearing screening
Adult who cannot do Behavioral testing
poor test agreeament

What type of patient might get a rate study or neurodiognistic ABR

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Aysmmetric HL
Unilateral tinnitus
Abnormal reflexes
Poor Speech recognition

why is Absolute latency the most robust and reliable characteristic and provides the mainstay of ABR interpretation?

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Becuase it is very repeatable and consistant across normal subjects

what do yo plot on your latency intensity fucntion?

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Plot wave 5
* based on the latency & stimulus level
* Latency (msec) - y-axis
* Simulus (db nHL) - x axis
* Run in 10 db increments (shaded is normal)
* Helps you to dtermine if your responses are within that noramtive range and you can determine type of HL

What are the four possible LIF types?

* **Normal** ( within shaded * **Cochlear** ( Higher intensities - normal, lower are prologanted) * **Conductive** (all W5 are prolongaed) * **Retrocochlear** (all W5 are prolongaed) Condutive & retrocohealr look the same on a LIF you would need BC or to see waves 1 & 3

Is amplitude affected by rate changes?

“Not really”- Hale * **faster rate = amplitude of wave 1 & 3 —> smaller amp** * it does affect latency * Slower the rate = earlier latency, cleaner the wave form Faster the rate = prolongation (longer) Latency of wave 5

How to enchance your wave 1?

* slower rate * higher intesnity * move electrodes closer to the generator site

What does an abnormal diagnostic ABR look like?

* latencies get porlonged * absnet peaks

# True or False The ABR tests the entire auditroy pathway and is able to test for cortical deafness.

FALSE The ABR does not evalute CNS above teh brainstem so cortical deafness cannot be ruled out of a normal ABR * doesnt differnate between types of lesions (acoutic and mengiioma will look the same)

why is the ABR not a hearing test?

We are only testing a very specific portion of the auditory system. We are not testing the cochlea or the higehr level areas * we are also not having people reposned * in 99% of the population you can estimate but it is still not a true test of hearing * You are looking at just one component to something

What stimulus do you use for a threshold ABR

Start w/ A click stimulus * do some high and low intensities * Click, 500,4,000 (could fill in a 1 or 2)

when are you going to do a BC ABR

In cases of * conductive HL * Pt's w/Atresia and you want to test the cochela

# True or False Threshold ABR equate to audiogram thresholds

FALSE You have to make some sort of correction factor . * it is not a direct comparison

# True or False Your latency will be earlier for your tone bursts than for clicks

FALSE you will have more prolonged latencies with tone than you would with click. = Later/increased latencies (also decreased amplitude)

When do BC latencies occur

Latency of wave V is slightly longer for BC clicks (than AC clicks) * Adults = increase in wave V latency ~ 0.6 ms * Children = increase in wave V latency ~ 0.7 ms

With bone-conducted ABR, stimuli rarely exceed __ to __ dB nHL

With bone-conducted ABR, stimuli rarely exceed **50 to 55 dB nHL**

what happens in BC ABR's if you incrase the intesnity to 65,75 or 80 and so on?

As you increase intensity the early waveforms will begin to disappear due to the transducer limits of the Bone oscillator. * BC ABR rarely exceed 50

What stimulus types are best for BC ABR?

**Click** is best tone burst can be used but not as perfered as click

Interpreat the ABR

Normal for the most part * absulte latencies are within normal range * Interwave latency are within normal range left ear wave 1 is it little outside of the norm but still will be take since eveyrthing * Contra's being decrased is normal since the signal attnuates throught anatomical structures

* Absolute latencies are pushed out, but the interwave latencies were retained within relatively normal limits * Wave V was replicable at 70 dB nHL but disappeared at 60 dB nHL

Condutive HL * Absolute latencies are pushed out equally, but the interwave latencies were retained within relatively normal limits - due to the attenuation from the obstruction * Wave V was replicable at 70 dB nHL but disappeared at 60 dB nHL

* Prolonged wave 1: Wave 1 showing prolonged latency (~ 2 ms) * Relatively normal Wave V: Wave V showing normal latency (~ 6 ms) * Latency-intensity function shows Wave V not repeatable at 45 dB nHL

ABR WITH A SNHL * because Cochlea is where the HL for SNHL occurs and is where wave 1 is generated from which is why wave 1 is prolonged but wave 5 is normal because the higher functions are normal (lateral lemniscus and Inferior colliculus)

* Right ear shows increased absolute Wave V latency = ~ 6.4 ms compared to ~ 5.5 ms for absolute Wave V latency for the left ear * Inter-aural Wave V latency difference = 0.9 ms (normal = 0.2 to 0.4 ms) * Interwave latency for right ear wave I-V = 5.1 ms (normal = ~ 4 ms)

Right Vestibular Schwannoma * Normal wave 1 - tells me normal inner ear * Prolonged wave 3 & 5 - higher cortical abnormality → retrocohlear * 1 - 5 Interwave latency is very important of retrocochlear pathology → increased 1 - 5 points towards retro * Normal left ear and a interaural different greater than norm

ANSD * Wave inverstion when you change polarity * Alternting polarity was a flat line

No increase in latency of wave V with decrease in intensity

ANSD * this is showing a Cochlear microphonic that is mimicking a ABR you can tell this because the wave 5 latency is not increasing with a decrease in intensity.

What is the latency of a cochlear microphonic

1 msec (occurs before wave 1) * CM are normal when they start and end before wave 1 * It is abnormal when it continues throughout the entire response like in ANSD

ask confused how this is effect of rate * CM is normal (occurs before W1) * Increase in wave V latency observed with increasing rate * Increasing rate shows poorer morphology for the left (affected) side but not on the right side * MRI indicated a 1.5 cm cerebello-pontine angle tumor indenting the left brainstem

Midterm Flashcards

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