Phasor admittance measurements of the middle ear. II. Normal phasor tympanograms and acoustic reflexes.

Phasor admittance trajectories obtained during tympanometry and acoustic reflex measurements at 220 and 660 Hz were obtained from 67 normal ears. The distributions of natural frequency and resistance derived from these phasor trajectories provide normative data for the technique. Median values of 817 and 714 Hz for natural frequency were obtained respectively for tympanometry and acoustic reflexes. Median resistances were 139 and 555 ohms. The distributions of these parameters from tympanometry and acoustic reflexes were significantly different for both resistance and natural frequency, supporting the assumption that the two procedures measure different aspects of middle-ear vibration, which we have attributed to ossicular chain vibration and to uncoupled vibration of the tympanic membrane. Correlation data are also consistent with this assumption.