title: Role of the mastoid in middle ear pressure regulation.
abstract: OBJECTIVE
  Determine the role of mastoid volume in middle ear pressure (MEP) regulation. The hypothesis was that inert gas exchange between blood and middle ear (ME) is slower for larger mastoid volumes.
  
  
  METHODS
  Prospective.
  
  
  METHODS
  For 21 enrolled subjects, the bilateral surface areas and volumes of the mastoid and tympanum were measured from computed tomography scans in 20 subjects with a wide range of mastoid volumes. Then, 19 subjects were reclined in a chair, fitted with a non-rebreathing mask and breathed room air for 20 minutes (acclimation), a gas composition of 25% N(2)O, 20% O(2), balance N(2) for 30 minutes (experiment), and room air for 30 minutes (recovery). Bilateral MEPs were recorded by tympanometry every 2 minutes. The slopes of the MEP-time functions during N(2)O breathing were calculated to the first observation of eustachian tube opening and divided by the estimated blood-ME N(2)O gradient to yield a N(2)O time constant. Sufficient data were available for 16 right and 11 left MEs to calculate the time constant.
  
  
  RESULTS
  MEP did not change during the baseline period, but within 10 minutes of breathing the N(2)O mixture showed a progressive increase. The right-left correlation for the time constant was 0.87 (n = 10 ears, P = .001). Regression of the time constants on ME volume showed an inverse relationship (n = 23 ears, r = -41, P = .05). A better data fit was the curvilinear relationship predicted by a mathematical model of the mastoid acting as a ME ear gas reserve.
  
  
  CONCLUSIONS
  These results support the tested hypothesis that the mastoid could serve as ME gas reserve.
authors.affiliation: Division of Pediatric Otolaryngology, Children's Hospital of Pittsburgh of UPMC, Department of Otolaryngology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15224, USA. alperc@pitt.edu
authors.forename: Cuneyt M
authors.initials: CM
authors.lastname: Alper
authors.forename: Dennis J
authors.initials: DJ
authors.lastname: Kitsko
authors.forename: J Douglas
authors.initials: JD
authors.lastname: Swarts
authors.forename: Brian
authors.initials: B
authors.lastname: Martin
authors.forename: Sancak
authors.initials: S
authors.lastname: Yuksel
authors.forename: Brendan M
authors.initials: BM
authors.lastname: Cullen Doyle
authors.forename: Richard J M
authors.initials: RJ
authors.lastname: Villardo
authors.forename: William J
authors.initials: WJ
authors.lastname: Doyle
mesh_terms: D000328:Adult; D004432:Ear, Middle / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008416:Mastoid / Q000033:anatomy & histology / Q000502:physiology*; D009609:Nitrous Oxide; D009929:Organ Size; D011312:Pressure; D011446:Prospective Studies
chemical_list: D009609:Nitrous Oxide