Tympanometry

Aka: Tympanometry, Tympanogram, Acoustic Reflectometry

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II. Indications

  1. Otitis Media
  2. Eustachian Tube Dysfunction
  3. Hearing Loss
  4. Otalgia

III. Background

  1. Measures Tympanic Membrane and ossicle stiffness
  2. Techniques
    1. Pneumatic Otoscopy
      1. Visualize Tympanic Membrane move to insufflation
    2. Tympanogram
      1. Recorded as pressure-versus-compliance curve

IV. Curve Types

  1. Type A Curve: Pressue near 0 with normal curve width
    1. Type Ad curve: High peak height (high compliance)
      1. Tympanic Membrane thinning (healed post-rupture)
      2. Ossicular disarticulation (increased pressure also)
    2. Type As curve: low peak height (low compliance)
      1. Middle ear effusion
      2. Ossicular fixation decreasing TM mobility
  2. Type B Curve: Flat curve (low compliance)
    1. See decreased compliance below (based on volume)
    2. Normal volume (e.g. middle ear effusion, sclerosis)
    3. Low volume (e.g. Cerumen Impaction)
    4. High volume (e.g. TM Perforation or tube)
  3. Type C Curve (high negative pressure): Retracted TM
    1. Eustachian Tube Dysfunction
    2. Upper Respiratory Infection

V. Findings: Compliance (measured along y or vertical axis)

  1. Normal compliance: 0.2 to 2.0 ml
    1. Reflects Tympanic Membrane mobility
    2. Measure air volume displaced by drum movement
  2. Increased compliance: flaccid Tympanic Membrane (Ad)
    1. Tympanic Membrane thinning (healed post-rupture)
    2. Ossicular disarticulation (increased pressure also)
  3. Decreased compliance (flat curves)
    1. Normal canal volume
      1. Flat curve (Type B)
        1. Middle ear effusion
        2. Scarred Tympanic Membrane (Tympanosclerosis)
        3. Cholesteatoma
        4. Middle Ear Tumor
      2. Convex peak with low compliance, normal volume (As)
        1. Middle ear effusion
        2. Ossicular fixation decreasing TM mobility
    2. Low canal volume, completely flat (Type B)
      1. Cerumen Impaction or ear debris present
      2. Incorrect probe placement
    3. High canal volume, flat curve (Type B)
      1. Tympanic Membrane Perforation (flat curve)
      2. Patent Tympanostomy Tube
      3. Prior mastoidectomy

VI. Findings: Pressure (measured along X or horizontal axis)

  1. Normal Pressure: +100 mmH2O to -150 mmH2O
  2. Negative Pressure (under -150 mmH2O)
    1. Eustachian Tube Dysfunction
  3. Increased Pressure (over 100 mmH2O)
    1. Ossicular disarticulation (increased compliance also)
    2. Some cases of Acute Otitis Media

VII. References

  1. Bredfeldt (1991) Am Fam Physician 44(6):2113-8 [PubMed]

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