Immittance typmpanometry and acoustic reflexes

  1. what does the term immittance refer to
    term used when refering ot both impedance and admittance
  2. impedance
    the opposition to flow of energy through a system
  3. admittance
    the ease which energy flows through a system
  4. what do changes in the middle ear produce
    pathological disturbances produce changes in the middle ear mechanical properties
  5. what are the approaches to the evaluation of the middle ear? and how?
    • direct-to observe the effect that a known force has on the system
    •      -apply a known force directly to the TM and measure its response
    •      -what will force do to ear drum
    • indirect-measure acoustic immittance of the air in the external auditory canal
    •      -why=because the acoustic characteristic of the air in the enclosed ear canal are partially determined by the middle ear
    •      -helps determine if there is presence of fluid in ME and site of lesion
  6. how is immittance of a mechanical system determined
    by exerting a force on the system and observing its response
  7. why is acoustic immittance important
    • measurements made in the plane of the tympanic membrane
    • force exerted and we look at the air pressure that bounces back
  8. force
    an action that is capable of moving a body or changing the motion of a body
  9. static and dynamic force
    • static=constant state, does not change with time
    • dynamic=changes over time
  10. mechanical force
    • when a force is applied to an object, the object moves with a velocity that is proportional to the applied force
    • relationship between the velocity and the applied force provides the basis for quantitative analysis of the immittance characteristics of the system
  11. when testing for impedance what are you really testing?
    really measuring compliance which is the inverse of stiffness
  12. what is compliance measured in
    cubic centimeters (cm3) or milliliters (ml) of an equivalent volume of air in the middle ear.
  13. what varies with frequency
    not acoustic resistance but the immittances of reactive elements
  14. what three things are made by measurements in the plane of the TM
  15. mechanical impedance
    the measure of how difficult it its to move
  16. what are the three characteristics of a mechanical system that determine its impedance
    • mass
    • compliance
    • friction
  17. what sort of system is the ear?
    • largely a stiffness dominated system at least in response to low freq sounds
    • mass factor=weight of ossicles and tm resistance ligaments that support ossicles stiffness load of fluid pressure from inner ear on the base of the stapes (how stiff is stapes in oval window.
  18. compliance
    • also called static acoustic admittance
    • mobility of the tm in response to a given vlaue of air pressure in the external canal
  19. when figuring static acoustic compliance what typically happens
    • intensity of probe automatically increases to 85-90 db avg volume for children and adults when vol can be determined in cc
    • then pressure is gradually decreased until tm achieved max compliance where the air pressure is equal on both sides of the tm
    • high vol may mean a perf, patent tube
  20. normative ranges for patients
    • age 3-10, compliance is .25 to 1.05 and vol is .3 to .9
    • >18, compliance is .30 to 1.70 and vol is .9 to 2.0
  21. tympanometry
    • tm vibrates most efficiently hen pressure on both sides is equal
    • pressure starts at +200 dapa and continues measurements as pressure in the canal is decreased (go all the way to -200 dapa) where is peak max compliance, least resistance?
    • purpose is to determine the point and magnitude of greatest compliance of tm
    • tests the middle ear pressure by noting the mobility of the tm as a function of various amounts of = and - pressure in the external canal
  22. immittance instrument
    • 3 samll plastic or rubber tubes attached to metal probe airtight seal
    • 3 tubes connected to a miniature loudspeaker that emits a pure tone, tiny microphone picks up sound from the canal, and an air pump
  23. what are the sorts of tympanic results
    • type a=normal middle ear function
    • type b=restriction of tm
    • type c=negative air pressure
  24. A, AS, AD
    • A=NORMAL
  25. Why do conductive losses affect the lower frequencies
    • because it takes more energy to get to the low freqs
    • conductive loss tends to stiffen the middle ear system
  26. what are the reflexes of the ear
    • acoustic and stapedial
    • combo of movement makes the eardrum move
  27. what is the acoustical reflex
    • the contraction of the middle ear muscles in response to sounds which has the effect of stiffening the middle ear system and decrease its static acoustic compliance
    • reflexive action to the sound of the stepedius muscle, causes stiffening of the tm
    • natural protection of the ear, these muscles make it so the sound is reduced if it is harsh
  28. tensor tympani and stapedius muscle
    • tone is presneted from 85-100 spl
    • reflex arc the pathway
    • helps determine site of lesion
    • tt is encased in small bony cavity 
    • inserts into the manubrium of the malleus and moves the malleus in such a way that the tympanic membrane becomes tense
    • innervation is from the trigeminal (vth cranial nerve)
    • reacts to movement
    • sm originates in the posterior wall of the middle ear
    • attaches to the posterior portion of the neck of the stapes
    • located in a canal beside the facial canal
    • reacts to sound
  29. what happens when the stapes contracts?
    • it moves to the side and tenses the membrane in the oval window
    • this contraction reduces the amp of the vibration
    • innervation by branch of the VII facial nerve
  30. how does the stapedius muscle and tensor typani respond
    • reflexively and bilaterally
    • in humans only stapedius responds to sound
    • tensor tympani can be caused to contract by air in the eac or eye an by changes in temp or touch in the eac
  31. acoustic reflex arc
    • ipsilateral acoustic reflex pathway/contralateral response pathway
    • outer ear→middle ear→inner ear→audio nerve→cochlear nucleus→superior olivary complex→facial nerve→middle ear crossover at the superior olivary complex to facial nerve to middle ear of opposite ear

  32. Possible outcomes of reflex
    • 1. reflex may be present at a normal sensation level (about 85 db)
    • 2. reflex may be absent a the limit of the reflex activating system (110-125 db)
    • 3. refelx may be present, in the case of a hearing loss, but at a low sensation level (less than 60 db above the audiometric thresh)
    • 4. reflex may be present, but at a high sensation level (greater than 100 db above the acoustic thresh
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Immittance typmpanometry and acoustic reflexes
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