TABLE 3-3 Norms for Peak Admittance (Y), Tympanometric Width (TW), and Equivalent Volume (Vec)

Age Group

Y (mmho)

TW (daPa)

Vec (cm3)






90th percentile range









90th percentile range





SOURCE: Margolis and Hunter (1999).

lent volume (Vec) (American Speech-Language-Hearing Association, 1990). Normal values for each of these parameters are shown in Table 3-3.

Peak admittance is the admittance value observed at the peak point on the tympanogram, in mmhos. Abnormally low values indicate a stiffening pathology of the middle ear, including otitis media with effusion and otosclerosis. Excessively high peak admittance values are consistent with a hypermobile middle ear system, such as ossicular discontinuity or scarring of the tympanic membrane.

Tympanometric width is the pressure interval on the tympanogram corresponding to a 50 percent reduction relative to the peak height. It is an indication of the shape of the tympanogram. A flat tympanogram, often associated with otitis media with effusion, produces an abnormally wide TW.

Equivalent volume is an indication of the volume of the external auditory canal. It is obtained at a pressure that minimizes the admittance of the middle ear (e.g., +200 daPa or -400 daPa). Thus, the height of the tympanogram at one of these values is the equivalent volume of the external auditory canal. Most acoustic admittance systems provide the Vec in a printout accompanying the tympanogram. Abnormally high Vec coupled with a flat tympanogram is observed in cases of a perforation of the tympanic membrane.

In summary, abnormal tympanograms are observed for a variety of pathological conditions affecting the tympanic membrane and middle ear, including otitis media with effusion, otosclerosis, ossicular discontinuity, tympanic membrane perforation, and a scarred (monomeric) tympanic membrane. A normal tympanogram indicates the presence of a normally functioning middle ear system, either with or without normal hearing.

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