title: Influence of rostral fluid shift on upper airway size and mucosal water content.
abstract: OBJECTIVE
  Fluid displacement from the legs during recumbency while in bed might narrow the upper airway (UA) in association with nuchal fluid accumulation that may contribute to the pathogenesis of obstructive sleep apnea (OSA). The aim of this study was to test the hypothesis that rostral fluid displacement from the legs causes a greater decrease in UA cross-sectional area (UA-XSA) and a greater increase in UA mucosal water content (UA-MWC) and internal jugular venous volume (IJVVol) in subjects with OSA than in those without OSA.
  
  
  METHODS
  Subjects underwent baseline assessment of leg fluid volume (LFV) measured by bio-electrical impedance, as well as UA-XSA and UA-MWC by magnetic resonance imaging. They were then randomly assigned to a 20-min period either with or without application of lower body positive pressure (LBPP) of 40 mm Hg, followed by a 15-min washout period, after which they crossed over to the other arm of the study. Measurements of LFV, UA-MWC, and UA-XSA were repeated after each arm of the study.
  
  
  RESULTS
  In 12 subjects without sleep apnea, UA-XSA increased and UA-MWC decreased significantly, whereas in 12 subjects with OSA, UA-XSA decreased and UA-MWC increased significantly in response to LBPP. The changes in UA-XSA and UA-MWC in response to LBPP differed significantly between the 2 groups (p = 0.006 and p < 0.001, respectively), despite similar changes in LFV and IJVVol.
  
  
  CONCLUSIONS
  Our results suggest that rostral fluid shift may contribute to the pathogenesis of OSA at least partly through narrowing of the UA due to transudation of fluid into the UA mucosa.
authors.affiliation: Toronto Rehabilitation Institute, Toronto, Ontario, Canada ; Departments of Medicine of the Toronto General Hospital University Health Network, Toronto, Ontario, Canada.
authors.forename: Takatoshi
authors.initials: T
authors.lastname: Kasai
authors.affiliation: Toronto Rehabilitation Institute, Toronto, Ontario, Canada.
authors.forename: Shveta S
authors.initials: SS
authors.lastname: Motwani
authors.affiliation: Toronto Rehabilitation Institute, Toronto, Ontario, Canada ; Departments of Medicine of the Toronto General Hospital University Health Network, Toronto, Ontario, Canada.
authors.forename: Rosilene M
authors.initials: RM
authors.lastname: Elias
authors.affiliation: Toronto Rehabilitation Institute, Toronto, Ontario, Canada.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Gabriel
authors.affiliation: Toronto Rehabilitation Institute, Toronto, Ontario, Canada ; Departments of Medicine of the Toronto General Hospital University Health Network, Toronto, Ontario, Canada.
authors.forename: Luigi
authors.initials: L
authors.lastname: Taranto Montemurro
authors.affiliation: Department of Cardiology, Juntendo University, School of Medicine, Tokyo, Japan.
authors.forename: Naotake
authors.initials: N
authors.lastname: Yanagisawa
authors.affiliation: Medical Imaging of the Toronto General Hospital University Health Network.
authors.forename: Neil
authors.initials: N
authors.lastname: Spiller
authors.affiliation: Medical Imaging of the Toronto General Hospital University Health Network.
authors.forename: Narinder
authors.initials: N
authors.lastname: Paul
authors.affiliation: Toronto Rehabilitation Institute, Toronto, Ontario, Canada ; Departments of Medicine of the Toronto General Hospital University Health Network, Toronto, Ontario, Canada ; Centre for Sleep Medicine and Circadian Biology of the University of Toronto, Toronto, Ontario, Canada.
authors.forename: T Douglas
authors.initials: TD
authors.lastname: Bradley
mesh_terms: D000328:Adult; D000403:Airway Resistance / Q000502:physiology*; D001834:Body Water / Q000502:physiology*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D017097:Electric Impedance; D005260:Female; D018495:Fluid Shifts / Q000502:physiology*; D005676:Gravity Suits; D006801:Humans; D007601:Jugular Veins / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D007866:Leg / Q000502:physiology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D017286:Polysomnography / Q000379:methods; D012137:Respiratory System / Q000033:anatomy & histology*; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: fluid displacement; lower body positive airway pressure; obstructive sleep apnea; upper airway cross-sectional area; upper airway mucosal water