title: Accuracy of tympanometric middle ear pressure determination in secretory otitis media: dose-dependent overestimation related to the viscosity and amount of middle ear fluid.
abstract: OBJECTIVE
  Tympanometric measurements of middle ear pressure in children with secretory otitis media are overestimated in a dose-response manner because of increased hysteresis explained by the viscosity and amount of middle ear fluid.
  
  
  BACKGROUND
  Tympanometric middle ear pressure is important in evaluating children with secretory otitis media. These measurements are influenced by hysteresis appearing as a peak pressure difference in bidirectional tympanometry. This represents an inaccuracy of 0.5 x peak pressure difference, which is only 5 to 25 daPa in normal ears. However, previous experiments found increased hysteresis, suggesting an inaccuracy of 225 daPa in secretory otitis media ears.
  
  
  METHODS
  In 56 patients with secretory otitis media, bidirectional tympanometry was performed; Type B curves were excluded. The middle ear fluid was semiquantified subsequently at surgery according to viscosity (serous, seromucoid, or mucoid) and amount (small, medium, or large). A control group included 28 normal children. Peak pressure difference was calculated by the difference between middle ear pressure determined by a positive and negative pressure sweep.
  
  
  RESULTS
  Mean peak pressure difference was 10 and 69 daPa in the normal and secretory otitis media groups, respectively (p <0.001). However, peak pressure difference ranged to 205 daPa in the secretory otitis media group and showed a significant positive correlation to viscosity and amount of the fluid (both p <0.0001).
  
  
  CONCLUSIONS
  Peak pressure difference is significantly increased in secretory otitis media because of additional damping explained by the viscosity and amount of the fluid. The mean error was 5 daPa in normal ears and 35 daPa in secretory otitis media ears, but ranged to greater than 100 daPa. These results were only a low estimate of the inaccuracy, because patients with Type B tympanograms could not be included, and errors of more than 100 daPa can be anticipated.
authors.affiliation: Department of Otolaryngology, Head and Neck Surgery, Aalborg Hospital, Aarhus University Hospital, Aalborg, Denmark. mgaihede@aas.nja.dk
authors.forename: Michael
authors.initials: M
authors.lastname: Gaihede
authors.forename: Mads
authors.initials: M
authors.lastname: Bramstoft
authors.forename: Lene T
authors.initials: LT
authors.lastname: Thomsen
authors.forename: Aksel
authors.initials: A
authors.lastname: Fogh
mesh_terms: D000158:Acoustic Impedance Tests / Q000706:statistics & numerical data*; D002648:Child; D002675:Child, Preschool; D004432:Ear, Middle / Q000502:physiology; D005122:Exudates and Transudates / Q000502:physiology; D005260:Female; D006801:Humans; D006874:Hydrostatic Pressure; D008297:Male; D008876:Middle Ear Ventilation; D010034:Otitis Media with Effusion / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D011237:Predictive Value of Tests; D012016:Reference Values; D015203:Reproducibility of Results; D013223:Statistics as Topic