Gas Supply, Demand and Middle Ear Gas Balance -- Preliminary Protocol
Condition: Middle-ear Function
Study type: Interventional

Summary: 
      The purpose of this study is to gather more information on Eustachian tube function and
      middle-ear pressures during flying. Ten subjects with tympanostomy tubes (plastic tubes
      inserted in the eardrums) in their ears or holes in their ear-drums will undergo flight
      simulation in a pressure chamber. Their middle-ear pressures and Eustachian tube function
      will be monitored at various chamber pressures.
    

Detailed description: 
      There are individuals who experience severe barotrauma/barotitis during airplane flights
      and/or free or tanked diving. Previously, one of the investigators modeled the change in
      middle-ear (ME) pressure during simulated airplane flights for ears with normal Eustachian
      tube function (ETF) and with different degrees of Eustachian tube (ET) dysfunction (Kanick
      SC, Doyle WJ. Barotrauma during air travel: predictions of a mathematical model. J Appl
      Physiol. May 2005;98(5):1592-1602). That model provided a number of important insights into
      the pathogenesis of ME barotrauma but included two assumptions that have not been validated:
      1) in the absence of ET opening, ME pressure is relatively stable (ignoring tympanic membrane
      volume induced changes) over wide ranges of ambient pressures, and 2) ET periluminal
      pressures track local ambient pressures. Other, less rigorous, descriptions of ME pressure
      behavior during flight and diving make different assumptions: 1) ME pressure changes with
      changes in ambient pressure and 2) ambient and ET mucosa pressures are incompletely coupled.
      Modeling ME pressure behavior using the two sets of assumptions predicts different ME
      pressure trajectories and explanations for barotitis/ME barotrauma during flight and diving.
      Because the behavior of ME pressure during flight (or diving) constrains the interventions
      that could be used to prevent barotitis/ME barotrauma, it is important to determine which, if
      either, model is correct.

      Ten otherwise healthy subjects aged 18 to 50 years with unilateral or bilateral eardrum
      perforations or ventilation tubes will be enrolled after obtaining Informed Consent. Complete
      histories will be taken with a focus on ear-related problems and they will have an ENT
      examination including tympanometry to document the patency of the ventilation tube and
      absence of drainage through the tube (disqualifiers). Eligible subjects will be studied in
      the pressure chamber during a typical flight simulation with periodic interruptions during
      ascent and descent. During the simulation, one ME will be fitted with an ear-canal probe
      attached to a pressure transducer and the other with a probe attached to the Forced-Response
      test system. ME pressure will be continuously monitored in the one ear and the
      Forced-Response test will be done at chamber pressures of atmospheric, on decreasing
      pressures (ascent in a flight) at 500 daPa intervals, during stable "cruising" cabin
      pressure, on increasing pressures (descent in a flight) at 500 daPa intervals and then at
      atmospheric pressure. All transducers will be referenced to chamber pressure and signals
      routed via an A-D box to the memory of a computer for on-line display and storage. Outcome
      variables will consist of the continuous measures of ME pressure in one ear and the periodic
      measures of ET opening pressure, closing pressure, passive resistance and dilatory efficiency
      in the contralateral ear.

      Under this model, it is expected that, between active/passive ET openings, ME pressure will
      be relatively stable and not affected by changing chamber pressure and that the measures of
      ET periluminal pressures (opening pressure, closing pressure and passive resistance) will
      track chamber pressure.
    

Intervention name(s): flight simulation
Intervention type(s): Other
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: flight simulation; middle ear; Eustachian tube function