Forward-backward tracing tympanometry in the diagnosis of middle ear pressure

Two tympanograms (TG) were routinely recorded on each ear by changing the pressure in the external auditory meatus (EAM), one in the decreasing (forward tracing: TG-F) followed by the other in the increasing direction (backward tracing: TG-B). Both TG were drawn on the same chart and the peak locations were compared. In a normal ear the TG-F peak tended to be formed in the negative pressure area and that of TG-B in the positive area. In a model whose middle ear pressure (MEP) was adjusted to the atmospheric pressure, the TG-F peak always indicated a negative pressure and that of TG-B a positive pressure value. As long as the same model was used, the magnitude of peak shift was identical irrespective of the middle ear pressure. The magnitude of the peak shift was influenced by the speed of EAM pressure change and a linear increase was observed up to the speed of 70 mmH2O/sec, both in a normal ear and a model. These findings seem to suggest that the peak location of a unidirectionally drawn TG can not be regarded as indicating the precise MEP. A valid MEP can better be estimated by averaging the peak pressure of TG-F and TG-B of forward-backward tracing tympanogram. In ears with pathology considerable variation was noted in the magnitude of the peak shift, so that relying solely on unidirectionally drawn TG could have lead to misdiagnosis in some cases. This was especially true with ears having small perforations covered with granulation or fluid.