Immitance

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  1. Impediance
    • the opposition to the flow of energy through a system
    • -sound strikes system and a portion is reflected back depending on the stiffness of the system.
    • -reflected wave carries info about the status of the middle ear
    • -harder surface has higher impediance
  2. Middle ear is stiff or immobile
    • greater amount of energy reflected back
    • -otis media or otosclerosis
  3. Flaccid system (middle ear)
    • will reflect less energy
    • -ossicular chain disruption
  4. admittance
    • how much energy is going into the system/how easy energy flows through
    • -ear with high impedance will have a low admittance
  5. Acoustic Immittance
    • a measure of impedance or admittance in order to get info about middle ear status
    • -fluid no fluid in middle ear?
    • -evaluate eustachian tube
    • -facial nerve function
    • -determine nature of hearing loss
    • -predict audiometric findings
  6. No drum movement
    no compliance or impedance measure
  7. Measuring intensity vs Pressure
    Compliance of the middle ear system
    • -if compliance is high impedance is low
    • -compliance is highest in centre of eardrum and lowest at edges
    • -negative and positive pressure push the eardrum in or out
    • -different pressures change the compliance of the eardrum and the impedance
    • -you push air in or out of the system to see when the eardrum is maximally compliant by monitoring tone changes
  8. Immittance test: Tympanometry
    • measurement of the mobility of the middle ear when pressure in the canal is varied from +200 to -400 daPa
    • -tells us 2 things
    • 1.middle ear drum peak pressure (normal is -150 to 50 daPa)
    • 2.where the eardrum moves best (normal is 0.3 to 1.6) lower than 0.3 is stiff and higher than 1.6 is flaccid
  9. Immittance test: Static acoustic immittance
    • -can infer volume of ear canal in cubic cm
    • -determine immittance ad +200daPa then immittance at most compliant point. The difference between the two = the equivalent ear canal volume(air space in canal)
    • -range of normal= 0.9 to 2.0 adults and 0.25 to 0.9 kids
  10. Type A Tympanogram
    peak pressure within normal range, height of peak tells us flaccid (Ad) if peak is too high and stiff if the peak is too low (As)
  11. Type B tympanogram
    • flat low volume, with no peak pressure meaning no drum movement
    • -lower than normal compliance
  12. Type C tympanogram
    peak pressure out of normal range, ear infection possibly
  13. Immittance test: Acoustic reflex
    • -They help you make sense of info you already know
    • -normal ears will have AR's at 500,1000,2000Hz at 65 to 95 db. higher than this is disordered
    • -elevated AR thresholds could mean conductive loss
    • -AR thresholds can help differentiate cochlear from retrocochlear pathology.
    • -with cochlear loss ARs are severe but present
    • -with retrocochlear lesions AR thresholds are not present
  14. Stapedious reflex
    • The lowest possible intensity required to elicit a middle ear muscle contraction
    • -reflex triggered in both ears
    • -contraction of the muscle results in temporary increase in impedance of middle ear
    • -if your drum is too stiff to move there is no reflex-if no reflex:inner ear, nerve, brain stem problems
    • -when reflex occurs impedance and sound pressure increase
Author:
Wesleypjones
ID:
316538
Card Set:
Immitance
Updated:
2016-02-26 17:45:40
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Immitance
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Immitance
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