title: Physiological gas exchange in the middle ear cavity.
abstract: OBJECTIVE
  Many reports pointed out that gas exchange in and out of the middle ear cavity occurs not only via the Eustachian tube but also across the middle ear mucosa. Our earlier study on children with otitis media with effusion (OME) for which a tympanic ventilation tube (TUBE) had been inserted revealed that the more severe the inflammatory change of the middle ear mucosa, the higher the degree of impairment of the transmucosal gas exchange function and the greater the decrease in the middle ear total pressure (METP). We hypothesized that the change in METP is caused by gas migration, and we conducted the present animal study to test this hypothesis and to determine the importance of METP measurement.
  
  
  METHODS
  Using 30 rabbits, ten in a group in which the middle ear cavity gas was replaced with atmospheric air (Group 1, oxygen (O(2)) 20%, carbon dioxide (CO(2)) 0.03% and nitrogen (N(2)) 79.9%), ten in a group replaced with a high CO(2) pressure gas whose partial pressure of CO(2) only was increased to 5% (Group 2, O(2) 20%, CO(2) 5% and balanced with N(2)) and ten in a group replaced with a low O(2) pressure gas (Group 3, O(2) 5%, CO(2) 0.03% and balanced with N(2)), changes in the METP were measured.
  
  
  RESULTS
  Group 1 showed a pressure change (increase, peak and then decrease in the METP) similar to that observed in a clinical cured group of OME with TUBE. In Group 2, no increase in the METP was observed and in Group 3 increase in the METP was observed but no decrease in the METP was observed.
  
  
  CONCLUSIONS
  It was found that the increase in the METP is attributable to diffusion of CO(2). This study elucidated that the change in the METP is a physiological response. Since the METP correlates with the degree of histologic inflammatory change in the middle ear mucosa, which was revealed in our clinical study of OME, it was reconfirmed that measurement of the METP is an important test method for evaluation of the degree of improvement in the pneumatic cavity mucosa.
authors.affiliation: Department of Otorhinolaryngology, Jikei University School of Medicine, 3-25-8 Nishishinbashi, Minato-ku, Tokyo 105, Japan. DZP00111@nifty.ne.jp
authors.forename: Yukio
authors.initials: Y
authors.lastname: Hamada
authors.forename: Hiroya
authors.initials: H
authors.lastname: Utahashi
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Aoki
mesh_terms: D000818:Animals; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000502:physiology; D004432:Ear, Middle / Q000502:physiology*; D008876:Middle Ear Ventilation; D009584:Nitrogen / Q000502:physiology; D010034:Otitis Media with Effusion / Q000503:physiopathology; D010100:Oxygen / Q000502:physiology; D011312:Pressure; D011817:Rabbits
chemical_list: D002245:Carbon Dioxide; D009584:Nitrogen; D010100:Oxygen