SHAPE AND DISPLACEMENT PATTERNS OF THE GERBIL TYMPANIC MEMBRANE IN EXPERIMENTAL OTITIS-MEDIA WITH EFFUSION

This study assesses the visco-elastic properties of the tympanic membr ane (TM) in isolated gerbilline temporal bones as a function of time a fter inducing experimental otitis media with effusion (OME). To do thi s we measured the TM displacements produced by application of sequence s of static pressures across the TM, with a high resolution, real-time , differential moire interferometer, and the results were compared wit h measurements on healthy ears. Two methods of producing OME were used : in one group tubal plugging was performed to produce mild OME (the ' TP group'); in the other group electro-cauterization of the nasopharyn geal orifice of the Eustachian tube was used to cause a severe form of OME (the 'EC group'). The measurements were performed from one day up to ten weeks after surgery. In the TP group the displacement fringe p atterns were normal, i.e. qualitatively they resembled the patterns of the control group. Quantitatively there was a significant decrease of displacement for a given pressure on the first day after surgery, fol lowed by a trend of increase with time; after seven to ten days the di splacement was larger than in the control group. In the EC group the d isplacement was significantly reduced after half a week, followed by a trend of increase with time, similar to what was found in the TP grou p; at one week the displacement was larger than in the control group, and at ten weeks the largest displacement was recorded. In the EC grou p the displacement patterns were often irregular; in some cases with c hanges suggesting the presence of weak spots in the TM where retractio n pockets most likely could develop. OME seems to affect the stiffness of the TM promptly so that it is a potential parameter for early diag nosis. The stiffness changes may, if measurable in the clinical situat ion, become prognostic parameters in the treatment of OME.