Computer-assisted curve-fitting techniques were used to describe quantitative and qualitative characteristics of normal tympanometric shape. The data base consisted of sets of triplicate tympanograms, obtained at 2-week intervals, from 7 2 ears of children with normal middle ears enrolled in the first through the fifth grades. A nonlinear equation produced significantly better prediction of normal tympanograms (R2 = 0.70) than did linear equations (R2 -= 0.44).bringing into question the use of the latter in determining normality. The complexity of applying curve fitting in clinical practice led to the development of a qualitative technique to determine normality. An initial application of the technique as a screen in 7 6 ears subjected to myringotomy produced a sensitivity of 96% and a specificity of 83% with respect to identification of the presence of middle ear fluid.A tympanogram is a record of the energy transfer characteristics of the middle ear as a function of pressure changes in the external canal. For a variety of reasons, shape seems to be of more clinical value than absolute indexes of energy tran~fer,~ although there is no consensus regarding description of shape. The most commonly used system of typing was introduced by Jerger4 and is based on the presence or absence of a peak and its location.Others have examined tympanometric shape more quantitatively. Liden et a1.8 proposed a system in which a tympanogram would be described by ( 1) the differences between energy transfer at +200 mm H 2 0 and -200 mm H20, (2) the width in millimeters of H20 of the tympanogram between its one-half of maximum energy transfer points, and (3) the pressure at which maximum energy transfer occurred. Brooks' addressed himself to a tympanogram's "gradient," calculated by dividing the change in energy transfer over a 100 mm H20 range in the area of the peak by the maximum change in energy transfer over the entire tympanogram. It is noted that ' Portions of this investigation were supported by Grason-Stadler.Inc., and Grant RFP-NIH-NINCDS-79-12 from the National Institute of Neurological and Communicative Disorders and Stroke.
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