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Abstract
Acoustic impedance and tympanometry data were obtained from 100 institutionalized mentally retarded children representing a broad range of ages, etiological classifications, and measured intelligence levels. Subjects had no known history of middle ear pathology and were demonstrated to have hearing within the normal range by behavioral pure-tone audiometry.
Tests included measures of absolute impedance (expressed in acoustic ohms), relative impedance (stapedius muscle reflex activity), and pressure-compliance relationship. All tests were performed using a Madsen ZO-70 electro-acoustic impedance meter and a standard pure-tone audiometer. Pressure-compliance curves were plotted graphically with an X-Y plotter.
Normative data, including measures of central tendency and intersubject variability, are reported for each or the criterion measures. A coustic reflex thresholds are presented with reference to the behavioral thresholds, and puretone-reflex threshold differences are discussed. Curves representing alterations in eardrum compliance with artificially induced ear canal pressure changes are illustrated. Measures of absolute impedance are also presented and are discussed with respect to the other tests. All test findings are related to existing data for normal populations. Potential clinical applicability of acoustic impedance measurements and tympanometry with mentally retarded persons is considered.
We have presented impedance and tympanometry test data from 100 normal hearing institutionalized mentally retarded subjects. Mean and median test results conform fairly well with data reported by other investigators, showing that the mentally retarded are essentially the same on these measures as normal subjects. Variability in general was greater than has been reported for normal subjects. This points to the possibility that some of the subjects may have had slight conductive problems that were not detected by pure-tone screening tests. If this is true, there is concomitantly further indication of the sensitivity of middle-ear impedance tests and, therefore, a need for more extensive application of these procedures, especially with difficult-to-test patients.