Tympanometric Middle-ear Pressure Determination with Two-component Admittance Meters

Exact tympanometric determination of the middle-ear pressure based on the location of the (central) extremum of susceptance, conductance, admittance, impedance, reactance or phase-angle tympanograms is not possible. None of these immittance components reaches its extremum exactly at middle-ear pressure neither at 220 nor at 660 Hz, due to the hysteresis caused by the viscoelastic behaviour of the soft biological tissue of the middle-ear structures. These effects cannot be avoided by lowering the rate of the pressure change during the recordings. The error on the middle-ear pressure determinations using a tympanometric method can be estimated to be of the order of 15 daPa.