title: Middle ear pressure change as a function of body position.
abstract: OBJECTIVE
  To verify and assess immediate middle ear (ME) pressure changes as a function of body position.
  
  
  METHODS
  A prospective clinical trail.
  
  
  METHODS
  Twenty-six adult volunteers having 52 normal, healthy ears had tympanometric ME pressures measured in an upright and recumbent positions. Recordings were obtained immediately after positioning and after 3 minutes. The main outcome measure was the pressure difference between upright and recumbent measurements, that is, positional ME pressure change.
  
  
  RESULTS
  All ME pressure recordings were within (-)100 to (+)55 mmH(2)O. An instant and significant (P < .001) pressure elevation was recorded in all ears once position changed from upright to recumbent. The average pressure increment was 19 mmH(2)O. Once a recumbent ear was repositioned upright it demonstrated an immediate pressure drop and regaining the initial ME pressure. Assuming the volume of a normal ME cleft as 8 mL and following Boyle's law, an ME volume alteration of about 17 microL was required to induce such pressure change.
  
  
  CONCLUSIONS
  Positional pressure changes were within the range of normal daily ME pressure variations. The instantaneous pressure changes and reversibility may be explained by filling and emptying of blood vessels within the ME cleft, following gravity causing an alteration of the aerated volume. Individual differences of pressure change may follow variability of ME cleft volume, its surface, and vessel density.
authors.affiliation: Department of Otolaryngology, Head and Neck Surgery, Edith Wolfson Medical Center, Holon, Israel. udicin@yahoo.com
authors.forename: Udi
authors.initials: U
authors.lastname: Cinamon
authors.forename: Eyal
authors.initials: E
authors.lastname: Russo
authors.forename: Dalia
authors.initials: D
authors.lastname: Levy
mesh_terms: D000158:Acoustic Impedance Tests; D000328:Adult; D000368:Aged; D004432:Ear, Middle / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture / Q000502:physiology*; D011312:Pressure; D011446:Prospective Studies