Tympanometric hysteresis effect and errors in middle ear pressure determination--a preliminary study in children with secretory otitis media.

Previous tympanometric studies on middle ear pressure (MEP) have revealed the hysteresis effect, which is illustrated in bidirectional tympanometries by the different peak pressures for either direction. This leads to an error in determination of MEP, which has been reported to be 10-25 daPa in normal ears, but experimental data have suggested that this error may be increased in ears with secretory otitis media (SOM). This was investigated in a group of 18 children with SOM by bidirectional tympanometries. The peak pressure difference (PPD) was calculated and found to be 75 daPa in the group of SOM, which was significantly larger than in normal ears (mean = 3 daPa) (p < 0.001). The maximum PPD in the SOM group was 205 daPa, indicating an error in MEP determination of more than 100 daPa. Hysteresis is related to the viscous properties of the middle ear system, and the increased hysteresis in SOM ears can be explained by the additional viscosity of the middle ear effusion. In order to improve the accuracy of MEP estimation it is suggested that in ears with SOM, the mean pressure of bidirectional tympanometries should be applied.