title: [Multi-frequency tympanometry in experimentally-induced cochlear lesions in chinchillas and guinea pigs].
abstract: OBJECTIVE
  To establish that susceptance-conductance tympanograms at a probe-tone frequency of 2 kHz reflects the status of the annular ligament (AL) and through it of the cochlea.
  
  
  METHODS
  Experimental study in 5 chinchillas and 22 guinea pigs. Six validating experiments were used: blockages of the stapes and of the round window membrane (RWM), fistula of the RWM, fluid removal from the cochlea, injection of saline in the scala tympani (ST) and acoustic trauma (AT). Quantitative data (mean values of Y226, FR, Y2000, G2000 and B2000) and shape of the curves were analyzed before and immediately after lesions were done.
  
  
  RESULTS
  Guinea pig was the most convenient provided bulla was vented and the same tip was used along the experiments. Only the shape of the curves are discriminant: 1/a supplementary sharp peak, centered around negative pressures, is observed in Y/G tympanograms in every case of RWM fistulas and in some case of AT. 2/injection of saline into ST induces immediate and reproducible Y2000, G2000, et B2000 curves modifications. 3/RWM and stapes blockages provoke foreseeable stiffening and sharpening of the tympanograms at 2 kHz. 4/on the contrary, fluid removal from the cochlea induces multiple peaks curves.
  
  
  CONCLUSIONS
  Experimentally-induced modifications at the AL either direct (stapes blockage) or indirect by AT or decrease/increase of pressure load at the cochlear interface at the footplate result in noticeable, constant, reproducible changes of curves registered at 2 kHz. The stapes behaves both as the plotter of the curves and the interpreter of the inner ear pressure.
authors.affiliation: C.H.U. Pellegrin, Clinique Universitaire O.R.L., Bordeaux, France.
authors.forename: V
authors.initials: V
authors.lastname: Darrouzet
authors.forename: J P
authors.initials: JP
authors.lastname: Erre
authors.forename: D
authors.initials: D
authors.lastname: Dulon
authors.forename: M
authors.initials: M
authors.lastname: Camicas Van Gout
authors.forename: J M
authors.initials: JM
authors.lastname: Aran
authors.forename: P A
authors.initials: PA
authors.lastname: Poutout
authors.forename: M
authors.initials: M
authors.lastname: Négrevergne
authors.forename: R
authors.initials: R
authors.lastname: Dauman
authors.forename: J P
authors.initials: JP
authors.lastname: Bébéar
mesh_terms: D000158:Acoustic Impedance Tests / Q000379:methods*; D000818:Animals; D002682:Chinchilla; D015834:Cochlear Diseases / Q000175:diagnosis*; D006168:Guinea Pigs