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Impedence audiogram(tympanometery)

  1. TYPE A - normal shape reflects a normal mechanism
    a. Ad - A deep curve with a tall peak indicates an abnormally compliant middle ear, as seen in ossicular dislocation or erosion, or loss of elastic fibers in the tympanic membrane, thin tympanic membrane (ie healing post rupture)
    b. As - A shallow curve indicates a stiff system, as in otosclerosis or middle ear effusion
  2. Type B - No sharp peak, with little or no variation in impedance over a wide range:
    a. normal volume -> middle ear fluid (non-compressible), sclerosis
    b. with abnormally small volume -> faulty probe, usually probe against wall or cerumen
    c. with abnormally large volume -> tympanic membrane perforation or PE tube
  3. Type C - Peak compliance is significantly below zero, indicating negative pressure (sub-atmospheric) in the middle ear space. This finding is often indicative of eustachian tube dysfunction.
  4. Type D: Notching: shows a dip in the peak. Indicates scarred eardrums or hypermobile TM

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