title: Change in upper airway geometry between upright and supine position during tidal nasal breathing.
abstract: BACKGROUND
  As the upper airway is the most important limiting factor for the deposition of inhalation medication in the lower airways, it is interesting to assess how its morphology varies between different postures. The goal of this study is to compare the upper airway morphology and functionality of healthy volunteers in the upright and supine positions during tidal nasal breathing and to search for baseline indicators for these changes. This is done by performing three-dimensional measurements on computed tomography (CT) and cone beam computed tomography (CBCT) scans.
  
  
  METHODS
  This prospective study was approved by all relevant institutional review boards. All patients gave their signed informed consent. In this study, 20 healthy volunteers (mean age, 62 years; age range, 37-78 years; mean body mass index, 29.26; body mass index range, 21.63-42.17; 16 men, 4 women) underwent a supine low-dose CT scan and an upright CBCT scan of the upper airway. The (local) average (Savg) and minimal (Smin) cross-sectional area, the position of the latter, the concavity, and the airway resistance were examined to determine if they changed from the upright to the supine position. If changes were found, baseline parameters were sought that were indicators for these differences.
  
  
  RESULTS
  There were five dropouts due to movement artifacts in the CBCT scans. Savg and Smin were 9.76% and 26.90% larger, respectively, in the CBCT scan than in the CT scan, whereas the resistance decreased by 26.15% in the upright position. The Savg of the region between the hard palate and the bottom of the uvula increased the most (49.85%). In people with a high body mass index, this value changed the least. The airway resistance in men decreased more than in women.
  
  
  CONCLUSIONS
  This study demonstrated that there are differences in upper airway morphology and functionality between the supine and upright positions and that there are baseline indicators for these differences.
authors.affiliation: 1 FluidDA, Groeningenlei 132, 2550 Kontich, Belgium .
authors.forename: Cedric S
authors.initials: CS
authors.lastname: Van Holsbeke
authors.forename: Stijn L
authors.initials: SL
authors.lastname: Verhulst
authors.forename: Wim G
authors.initials: WG
authors.lastname: Vos
authors.forename: Jan W
authors.initials: JW
authors.lastname: De Backer
authors.forename: Samir C
authors.initials: SC
authors.lastname: Vinchurkar
authors.forename: Pascal R
authors.initials: PR
authors.lastname: Verdonck
authors.forename: Johanna W D
authors.initials: JW
authors.lastname: van Doorn
authors.forename: Nasser
authors.initials: N
authors.lastname: Nadjmi
authors.forename: Wilfried A
authors.initials: WA
authors.lastname: De Backer
mesh_terms: D000328:Adult; D000368:Aged; D000403:Airway Resistance; D054893:Cone-Beam Computed Tomography; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011857:Radiographic Image Interpretation, Computer-Assisted; D012119:Respiration; D012137:Respiratory System / Q000000981:diagnostic imaging*; D012737:Sex Factors; D016683:Supine Position; D014057:Tomography, X-Ray Computed