Week 9 Suppression Flashcards
disorders associated with ANSD (6)
- anoxia
- hyperbilirubinemia
- immune disorders
- mitochondrial diseases
- neurological disorders (charcot-marie-tooth)
- syndromes like waardenburgs
what is ANSD
impairment of the peripheral auditory function with the preservation of OHC integrity
site of lesion with type I ANSD
impaired function of the auditory nerve due to demyelination
site of lesion with type II ANSD
lesion involving the IHC or the synapses between the IHC and the nerve fibers
what are the 3 impacts of demyelinization
1) affects the high discharge rate associated with loud sounds which affects loudness encoding
2) more sensitive to temperature changes
3) cross-talk between fibers (one fiber activates its neighbor)
SP/AP with dysynchrony of afferent fibers
there will not be a nice SP/AP, neural discharge patterns change with demyelinization or axon loss (causes fibers to no longer fire at the same time, making the signal weaker)
audiogram with ANSD
can be any degree and configuration (SNHL)
speech testing with ANSD
disproportionately affected in comparison to audio
—particularly affected by noise
acoustic reflexes with ANSD
absent, but can be present and abnormal
ABR with ANSD
abnormal (absent or delayed wave V)
OAEs and CM with ANSD
typically present
vestibular testing with ANSD
can be abnormal but they are normally asymptomatic
what polarity should be used when testing suspected ANSD with AEP
both condensation and rarefaction instead of just alternating to give more info
what rate should be used when testing suspected ANSD with AEP
if expecting neuropathy, want to do slower rate than the normal 27 clicks /sec because the nerve is struggling so maybe 11 clicks/sec or 3 clicks/sec to show better response
success of CI with ANSD
- pts with ANSD can be CI candidate
- -if site of lesion is IHC they should do well with CI
- -if site of lesion is demyelination of auditory nerve, they probs wont do very well with CI (maybe better than HAs though)
MOC fibers compared t LOC fibers
MOC is thicker, more myelinated, and synapses direction to the OHCs it innervates while LOC synapses on the nerve fibers of the IHCs
crossed and uncrossed fibers of the MOC vs LOC
- 2/3 of the LOC are uncrossed, 1/3 of the MOC are crossed
- –this means they are activated during contra stimulation
- 2/3 of the MOC and 1/3 of the LOC is crossed
- –this means they are ipsilateral
three potential functions of the auditory efferent system
1) protect from acoustic trauma
2) hearing in noise
3) attention
five subject factors influencing suppression
- inhibition increases with developmental age (infancy to childhood)
- reduction in inhibition is associated with older age, with greater reduction for binaural stimulation
- females have more suppression than males
- right ear has more than left
- SNHL affects suppression, also also have less robust or absent OAEs so harder to evaluate suppression
suppression with SOAEs and SFOAEs
- some studies have focused on these
- nice because not interfering wiht what is going on in same ear
- won’t activate acoustic eflec
- stimulus cant cancel out the response
- with SOAEs, activating efferent system equals a decrease in amplitude of the response
- also can cause a frequency change of the response of usually about 5 Hz, but up to 30 Hz, however, not all normal hearing adults have SOAEs
suppression of DPOAEs and TEOAEs
frequnecy of the response will not change with suppression, but response is suppressed and loses amplitude
two different factors that can have an affect on the attempted measurement of the efferent system
- acoustic reflex, which would also reduce the response
* mechanical suppression which is when there are two traveling waves and one cancels the other out
problems with bilateral or ipsilateral presentation of the suppression noise for OAEs
- could show either the effects of the efferent system, the acoustic reflex, or mechanical suppression
- –the latency of mechanical suppression is shorter than latency of AR and efferent activation affecting response
what needs to be done with bilateral or ipsilateral suppression to ensure what is seen is resulting from the efferent system
- use forward masking paradigm to see response to click without having mechanical suppression with still having efferent suppression
- to avoid having effect of acoustic reflex in response, need to have click at an intensity that is not loud enough to activate acoustic reflex
- –this would leave only the efferent effect
contralateral stimulation advantage
just worried about acoustic reflex being activated, dont have to worry about mechanical suppression
- –can now present click and noise at the same time
- –however contra effect is small compared o bilateral stimulus which gives largest effect
what works best to suppress TEOAEs
BBN signals, the greater the bandwidth of the noise, the greater the effect
how to best suppress pure tone
elicitors 0.5-1 octave below the OAE evoking stimulus
how to measure contra ellicitor suppression
- measure OAEs with no noise
- present noise in contra ear and measure OAE response again
- –the difference between the two is the efferent system
how to measure ipsi elicitor suppression
- present noise to activate efferent system
- wait a bit and the measure OAEs
- —lose some of the efferent system effect because the latency is only about 5-10ms
- –fast decays in 10-100 ms after noise is turned off and wait 40-50 msec to measure when testing
is a lower or higher intensity better for suppression
- lower intensity is better
- –TEOAEs: click stimuli between 50-60 dB peSPL vs 80 dB peSPL
- –DPOAE: stimulu less than 60-65 dB SPL
best frequencies to see suppression with DPOAEs
1.5-4kHz (note the cubic difference tone 2F1-F2 shows less suppression than the quadratic difference tone F2-F1
best frequencies to see suppression with TEOAEs
1-2kHz
measuring ECochG suppression
AP is suppressed in amplitude with OCB activation
- CM amplitude is increased wit MOC activation
- –efferent system increases the amount of voltage change in OHCs so CM increases
- ——-AP is suppressed because the signal is reduced to the neurons
- not much change to ECochG with ipsi, but with contra there is change
factors in children leading to reduced suppression
- chemo
- poor academic performance
- “auditory listening problems”
- ANSD
- autism
factors in adults leading to reduced suppression
- unilateral acoustic tumors
- migraine
- tinnitus
risk factors for HL as per joint committee on infant hearing screening
- family Hx
- infection associated with HL
- bacterial meningitis
- craniofacial anomalies
- low birth weight (3lbs 5 oz)
- hyperbilirubinemia (requiring exchange transfusion)
- asphyxia (APGAR 0-3 at five minutes)
- NICU stay for more than 48 hours
4 reasons why OAEs are helpful in hearing screening
- robust
- linked to low thresholds
- quick to obtain
- noninvasive
standard TEOAE protocol
- 20 ms recording window
- click rate of 50/sec
- click stimulus
QuickScreen protocol TEOAE
- 12.5 msec recording window
- click rate of 80/sec
- stimulus: click
normal TEOAE amplitude for infants
20 dB SPL +/- 5 dB
normal TEOAE amplitude for adults
12 dB SPL +/- 5 dB
most common ratio of f1/F2 in DPs
1.2 for infants, children, and adults
difference in DP amplitude and noise between adults and infants
- babies amplitude is 10 dB larger across frequencies
* below 3000 Hz is more noise in infants by 5-15 dB
difference in OAEs between preterm and full term babies
- TE and DP of preterm is lower than full term in amplitude
- still higher than adults
- increased levels as gestational age increased
factors affecting OAE fail rate in babies
- different pass criteria
- number of attempts before leaving hospital
- nursery type (NICU vs WBN)
- age at screening (in hours/days)
- software parameters (protocol used)
two common types of middle ear dysfunction in infants
- vernix caseosa in the ear-canal, can be fully occluding
* amniotic fluid which can stay in the middle ear for up to 24 hours after birth
