Forward–Backward Tracing Tympanometry

Abstract

Two tympanograms were routinely recorded from each ear by altering the pressure in the external auditory meatus (EAM), first in the decreasing direction (Forward Tracing: TG-F) and next in the increasing direction (Backward Tracing: TG-B). In a normal ear the TG-F peak tended to be in the negative pressure area and that of the TG-B in the positive area. When the middle ear pressure was adjusted to the atmospheric pressure in a model, the TG-F peak always indicated a negative pressure and that of TG-B always showed a positive pressure value. As long as the same model was used, the magnitude of the difference of the two peaks was identical irrespective of the middle ear pressure, but it was influenced by the speed of EAM pressure change, and a linear increase was observed up to the speed of 70 mmH₂O/s, both in the normal ear and in the model. In ears with pathology, considerable variation was noted in the magnitude of the peak shift. These findings seem to suggest that the peak location of a unidirectionally drawn tympanogram cannot be regarded as indicating the precise middle ear pressure. The middle ear pressure can be estimated more accurately by averaging the peak pressures of TG-F and TG-B of Forward-Backward Tracing Tympanogram.

Key Words:

• tympanogram peak
• sweep direction
• middle ear pressure
• eardrum perforation