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Describe the acoustic stapedius reflex. What are the two muscles in the middle ear and what is each innervated by?What do these muscles do in response to loud sounds and tactile stimulation? What does this do? What are the functions of the reflex?

  • Two muscles in the middle ear:
    • tensor tympani; innervated by N. V (trigeminal)  
    • stapedius; innervated by N. VII (facial)
      • Inserts into head of stapes, will pull ossicular chain in different direction
  • These muscles contract in response to loud sounds and tactile stimulation (reflex)
    • contraction --> stiffening of middle ear system
    • causes decrease in acoustic Y
    • Sounds wont be transferred as well and will be reflected back. 
  • Functions of the reflex:
    • protect inner ear from intense acoustic stimuli
      • not perfect, prevents primarily low frequency transmission
      • Takes some time for muscle to contract so some energy can get through beforehand.
    • Affords an advantage for listening to speech in noise (ASR attenuates low frequency signals - noise)
      • Enhances SNR


What are the ipsilateral and contralateral stapedius reflex pathways?

  • Ipsilateral
    • Cochlea -> Ventral cochlear nucleus -> medial superior olive ->EITHER facial nerve motor nucleus OR directly to facial nerve -> stapedius
  • Contralateral
    • Cochlea -> Ventral cochlear nucleus -> medial superior olive -> facial nerve motor nucleus (contralateral) -> facial nerve -> stapedius


Describe contralateral stimulation. What is assessed with the stimulus? What is assumed to be intact? What is the ear that receives the stimulus called? Where does the acoustic reflex contract? Where is the contraction monitored? What happens when the contraction occurs? 

  • Contralateral stimulation
    • acoustic stimulus presented to afferent side (the “activator” ear) - afferent portion of auditory system assessed with stimulus
      • Because we are assessing the afferent portion of the auditory system
      • We assume that the efferent portion of the acoustic reflex arc is intact
      • Ear that receives the stimulus is the activator/test ear*****
    • acoustic reflex contracts bilaterally
    • however, we monitor reflex contraction in opposite ear (the probe ear)
    • when contraction occurs -> change in stiffness of ME system
      • observed as a decrease in Y of probe tone in the “probe” ear


What is the definition of the acoustic reflex threshold? How is the acoustic reflex threshold measured?

  • Definition of acoustic reflex threshold: the lowest intensity level of acoustic stimulus at which a minimal change in ME admittance can be monitored, which is time-locked to stimulus presentation
  • Measurement of acoustic reflex threshold
    • increase sensitivity scale; probe is presented continuously
    • apply pressure that yielded max. point on tympanogram
      • Start button pressurizes ear
    • present acoustic stimuli to test ear (500 -2kHz; 4kHz -optional)
    • initial stimulus level: 70 dB HL; ascend in 5-dB steps
      • Take reflex at ascending to avoid reflex sensitization
    • stimulus duration: 1-2 sec
    • look for a change of .02 or more mmhos (or as defined by manufacturer’s norms)


What is the normative data for contralateral ASR?

  • Normal-hearing subjects:
    • ASR Θs for pure tones are 70-90 dB SL above behavioral p.t.Θ (Metz, 1952) 
    • Wiley et al. (1987): Mean contralateral ASR Θs in young adults with normal hearing: 
      • 500 Hz 84.6  6.3
      • 1000 Hz 85.9  5.2
      • 2000 Hz 84.4  5.7
      • 4000 Hz 89.8  8.9
    • See Silman & Gelfand (1990) charts for 90th percentile cutoffs.


What are expected results of contralateral acoustic reflex threshold with disorders? Conductive loss, cochlear lesions, retrocochlear and brainstem lesions? facial nerve paralysis?

  • Subjects with conductive loss: ARTs are absent
    • Test ear, cond. HL attenuates signal
    • 10 dB or more of cond. component 
  • Subjects with cochlear lesions: ARTs elicited at reduced SL’s
    • Dynamic range from threshold to reflex: 20 –70 dB SL
    • If ART is elicited at < 60 dB SL:  + sign for recruitment  
    • ARTs will be elicited within 90th percentile range re: Silman & Gelfand (1990) charts (median ASR thresholds <95 dB HL for HL <60 dB HL)
      • 90th percentile with behavioral threshold
  • Subjects with retrocochlear and brainstem disorders:
    • vestibular schwannoma:  ARTs elevated/absent (> 90th percentile)
      • Even if elevated for one freq will suspect NVIII lesion
    • Auditory neuropathy spectrum disorder (ANSD):  ARTs are elevated or absent in most cases (Berlin et al., 2005)
    • Intra-axial brainstem disorders: can see absent/elevated contralateral reflexes
      • If its the only issue, will see normal pt thresholds
  • (Above results assume you can view contraction in probe ear)
  • Subjects with facial nerve paralysis (Bell’s Balsy): ARTs absent in probe ear


When will contralateral acoustic reflexes be absent?

  • Bilateral or unilateral conductive hearing loss
    • 25+ dB HL conductive component in test ear
    • 10+ dB HL conductive component in probe ear
  • Severe-to-profound sensorineural hearing loss in test ear (> 80 dB HL)
    • Alternative to pure tone stimuli: use wide-band noise
      • Loudness grows more rapidly in wideband noise (elicited at 65-72 for NH)
  • N. VIII lesion (mild or moderate sensorineural loss in test ear)
  • N. VII disorder in probe ear, if lesion is central to stapedial tendon
  • Brainstem lesion affecting crossing fibers


What are additional less likely reasons that a contralateral acoustic reflex will be absent?

  • post stapedectomees
  • absent stapedius muscle
  • perforated TM
  • wax in external auditory canal
  • malfunctioning equipment


Explain ipsilateral reflex stimulation. What are the advantages over contralateral stimulatio only? Where are stimuli present? How much better are ipsilateral reflexes usually? What is more limited? why?

  • Presentation of stimulus and monitoring of probe in same ear
  • Advantages over contralateral stimulation only
    • no longer dependent on status of probe ear
    • insert probe assembly in stimulus ear prevents ear canal collapse
  • stimuli presented: 500 -2kHz
  • ARTs are often about 5 dB better with ipsilateral presentation than with contralateral presentation  
  • output level more limited than with contralateral stimulation
    • Due to artifacts of presenting stimulus and recording response in same ear


What is the effect of otosclerosis, osteogenesis imperfecta, cogan's syndrom on the the acoustic reflex? Drugs? Alcohol? Age? probe level?

  •  Otosclerosis, osteogenesis imperfecta, Cogan’s synd., etc.
    • biphasic at onset and offset
    • monophasic - one in onset and offset
    • biphasic - two directions 
      • normal if at onset only
  • Use of drugs 
    • elevated with barbituates
    • absent with psychotic drugs or alcohol use
  • Use of alcohol
  • Age
    • Infants –effect of probe frequency
      • 226 Hz - high proportion so not show reflex
    • Advanced age –effect of stimulus type
      • tones - does not change with age
      • broad band - see age effects - elevated threshold
  • Probe level
    • Standard level = 85 dB SPL
    • With ↑ in probe level (from 70 -> 85 dB SPL), ART ↓ (Day & Feeney, 2008)


Explain the study that found the acoustic reflex adaptation. What do results with normal and NVIII lesions show?

  • Study by Anderson, Barr, & Wedenberg (1969)
  • presented tone 10 dB SL re: ART, at 500 -4kHz
  • recorded response for 10+ sec
  • response for normal S’s varied with frequency
    • At 500 and 1k Hz –reflex contraction was stable
    • At 2kHz and 4kHz –reflex contraction decreased over time
  • response for S’s with N. VIII lesions at 500 and 1kHz very different than for normal S’s
    • decreased over time for 500 and 100 Hz - 50% within 10 sec


What is the clinical procedure for acoustic reflex adaptation? What is the max level of presentation? What is significant adaptation? What is the sensitivity and specificity for identifying NVIII lesions?

  • Clinical Procedure
    • obtain ART at 500 Hz and 1000 Hz  
    • present tone at 10 dB SL re: ART (max level: 115 dB SPL)
    • record response for 10 sec; assign 100% to initial amplitude
    • if amplitude decreases > 50% before 10 sec, this is significant adaptation
  • Sensitivity/Specificity:
    • 80-85% (for identifying N. VIII lesions)


What are refined criteria for significant adaptation?

  • Hirsh and Anderson (1980)
    • Monitor reflex contraction for 5 sec at .5 and 1kHz
    • If amplitude declines >50% at both frequencies within 5 sec -> (+)  result for retrocochlear lesion
    • If amplitude declines >50% at 1k Hz, but not .5 kHz within 5 sec -> questionable adaptation
    • If amplitude declines < 50% within 5 sec at both frequencies -> (-) result for retrocochlear lesion


Describe the differential diagnosis value of acoustic immittance.

  • Differentiate conductive vs. sensorineural lesion
  • Differentiate cochlear v. N. VIII lesion
    • If within 90% - cochlear
    • If higher - retrocochlear
  • Determine Eustachian Tube sufficiency
    • Eustachian tube function test
  • Identify perforation of tympanic membrane
  • Detect pseudohypoacusis
    • reflexes - comparison to pt thresholds
  • Detect site of N. VII paralysis
    • Absent reflexes probe ear - can monitor recovery
  • Detect brainstem lesions
    • Compare contra and ipsi
      • normal ipsi, absent contra