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Static and Dynamic Acoustic Impedance Measurements in Infant Ears

Gerald R. Popelka
University of Wisconsin, Madison, Wisconsin

Tympanometry and acoustic reflex threshold data are reported for a series of presumably normal infants ranging in age from 55 to 132 days. In general, tympanograms displayed single peaks between ±50 mm H₂O. Susceptance tympanograms with a 660-Hz probe frequency were sometimes characterized by monotonically increasing susceptance as ear canal pressure was changed from –200 to +200 mm H₂O. Static values of acoustic conductance, susceptance, admittance, resistance, reactance, impedance, and phase angle were computed from tympanograms using the values of ambient and +200 mm H₂O (0/+200 procedure) and the maximum and minimum tympanometric values (MAX/MIN procedure). Comparison of the data from the two computational procedures suggested that the MAX/MIN procedure produces means and standard deviations of static values which are more manageable for establishing confidence limits with which to evaluate potentially pathological subjects. The MAX/MIN procedure resulted in lower mean values of conductance and susceptance for infant subjects relative to previously reported adult data using a similar computational procedure. Acoustic reflex thresholds were clearly present in all testable infants at coupler sound pressure levels similar to adult data, suggesting that the relations between reflex thresholds and hearing sensitivity demonstrated in adult subjects are similarly applicable to infant subjects. Mild sedation to induce sleep without altering the reflex would make acoustic reflex threshold measurement a useful procedure for screening large numbers of infants.

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