title: Tympanometric experiments on retracted ear drums--does tympanometry reflect the true middle ear pressure?
abstract: CONCLUSIONS
  Tympanometry in ears with retracted or partially atelectatic tympanic membranes does not reflect the true middle ear (ME) pressure. The position of the tympanogram peak depends on the size of a retraction pocket and the remaining ME gas volume. Thus tympanometry in such cases cannot be used for measurements of ME pressure.
  
  
  OBJECTIVE
  To prove the hypothesis that tympanometry in ears with retraction pockets or atelectasis does not measure ME pressure correctly.
  
  
  METHODS
  Tympanometry was performed in a simplified artificial ME model, in which different 'tympanic membranes' with pockets could be integrated.
  
  
  RESULTS
  We found a shift of the tympanogram peaks, either towards negative or positive pressures, depending on the position of the pocket: in case of an 'inward' direction (towards the ME like a retraction pocket) the peak was in the negative pressure range, in case of an 'outward' direction (bulging into the ear canal) the shift was towards positive pressures. The shift increased with decreasing volume behind the tympanic membrane. The effect cannot be simply be explained by hysteresis but by the air 'cushion' that is 'trapped' behind the membrane, limiting its excursions during the tympanometric sweep.
authors.affiliation: ENT Department, Medical School, University of Rostock, Rostock, Germany. hans-wilhelm.pau@med.uni-rostock.de
authors.forename: Hans Wilhelm
authors.initials: HW
authors.lastname: Pau
authors.forename: Christoph
authors.initials: C
authors.lastname: Punke
authors.forename: Tino
authors.initials: T
authors.lastname: Just
mesh_terms: D000158:Acoustic Impedance Tests; D004432:Ear, Middle / Q000502:physiology; D006801:Humans; D008953:Models, Anatomic; D011312:Pressure