title: Transmucosal O2 and CO2 exchange rates for the human middle ear.
abstract: OBJECTIVE
  Estimate the transmucosal CO(2) and O(2) rate-constants for adult middle ears (MEs).
  
  
  METHODS
  Ten adults with healthy MEs had a unilateral myringotomy. A custom-fitted acrylic mold with a valved line to a mass spectrometer (MS) and central tube coupled to a 3-way valve and connected to a pressure transducer (the probe) was sealed with adhesive glue within the ipsilateral ear-canal. A second 3-way valve was attached to the probe valve, a flow-regulated tank gas source and paired syringes. Volumes of the ME and probe were measured. On sequential days, the probe+ME was washed for 15-min with 6% O(2), Balance N(2) and 25% O(2), 6% CO(2), Balance N(2) to create transmucosal CO(2) and O(2) gradients, respectively. After washing, the probe+ME was isolated from the gas source, and baseline and 10-min gas samples were obtained for MS analysis of gas partial-pressures. The rates of change in ME CO(2) and O(2) pressures were divided by their established transmucosal gradients to yield CO(2) and O(2) rate-constants.
  
  
  RESULTS
  The average (±STD) transmucosal CO(2) and O(2) rate-constants were 0.062 ± 0.034 (N=10, range: 0.032-0.119) and 0.011 ± 0.009 (N=8, range: 0.002-0.032)mmHg/min/mmHg, respectively. The average half-life for the CO(2) and O(2) gradient was 11.1 and 61.6 min. The average CO(2):O(2) rate-constant ratio was 8.1 ± 4.0 (N=8, range: 3.6-14.6).
  
  
  CONCLUSIONS
  For adult human MEs, transmucosal CO(2) exchange is rapid and much faster than transmucosal O(2) exchange. The estimated CO(2)/O(2) rate-constant ratio for the human ME is not consistent with that predicted for diffusion-limited gas exchange across a water-based barrier.
authors.affiliation: Division of Pediatric Otolaryngology, Department of Otolaryngology, Children's Hospital of Pittsburgh of UPMC, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA. docdoyle2@aol.com
authors.forename: William J
authors.initials: WJ
authors.lastname: Doyle
authors.forename: J Douglas
authors.initials: JD
authors.lastname: Swarts
authors.forename: Juliane
authors.initials: J
authors.lastname: Banks
authors.forename: Sancak
authors.initials: S
authors.lastname: Yuksel
authors.forename: Cuneyt M
authors.initials: CM
authors.lastname: Alper
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000032:analysis*; D004432:Ear, Middle / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009092:Mucous Membrane / Q000502:physiology; D010100:Oxygen / Q000032:analysis*; D010313:Partial Pressure; D014432:Tympanic Membrane / Q000502:physiology
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen