Tympanometry is clinically important in that it allows identification of middle ear pathology. The tympanogram is a graphic plot of changes in the immittance of the middle ear vibratory system against air pressure that is varied in the external ear canal. Air pressure is measured in decaPascals (daPa). Immittance of the middle ear is measured in millimhO (mmhO) or cm3 (cc).

A normal shaped tympanogram is designated type A. Abnormally shaped tympanograms, such as the following, occur when there is a middle ear disorder.
    Normal Values for Immitance Audiometry:
  • Tympanogram Middle ear pressure Physical volume Static compliance
    Type A -150 to +50 daPa 0.6-1.5 cc 0.28-2.0 cc
    Type B No Peak 0.6-1.5 cc <0.28 cc
    Type C <-150 daPa 0.6-1.5 cc 0.28-2.0 cc