title: Phasic respiratory pharyngeal mechanics by magnetic resonance imaging in lean and obese zucker rats.
abstract: BACKGROUND
  Although obstructive sleep apnea is strongly associated with obesity, we have little understanding of how obesity may alter the mechanical properties of the pharynx and the role of obesity in the pathogenesis of sleep apnea.
  
  
  OBJECTIVE
  The overall objective of this study was to determine the effect of obesity on pharyngeal airway size and pharyngeal wall tissue strain in lean and obese Zucker rats.
  
  
  METHODS
  Respiratory-gated magnetic resonance imaging with noninvasive tissue tagging was performed in anesthetized, spontaneously breathing lean (n = 9) and obese (n = 9) Zucker rats. Images acquired during expiration and inspiration of the rostral, mid-, and caudal pharynx were analyzed for airway size and pharyngeal wall tissue strain, using planimetry, optical flow, and finite element analyses. Differences in cross-sectional airway area, lateral and anteroposterior airway diameters, and tissue strain (stretch, compression, and direction of stretch) in the lateral and ventral pharyngeal walls were compared by analysis of variance (significance at p < 0.05).
  
  
  RESULTS
  Compared with their lean littermates, obese rats had the following significant findings: reduced pharyngeal airway cross-sectional area during inspiration and expiration, smaller increases in airway area during inspiration, and decreased lateral airway dilation during inspiration. Tissue strain in the pharyngeal walls showed no significant differences between obese and lean rats.
  
  
  CONCLUSIONS
  These findings suggest that obesity results in a mechanical abnormality that decreases pharyngeal airway size and prevents a normal airway response to a given change in pharyngeal wall tissue strain.
authors.affiliation: Center for Sleep and Respiratory Neurobiology, University of Pennsylvania, Maloney Building, 3600 Spruce Street, Philadelphia, PA 19104, USA. brennick@mail.med.upenn.edu
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Brennick
authors.forename: Stephen
authors.initials: S
authors.lastname: Pickup
authors.forename: Jacqueline R
authors.initials: JR
authors.lastname: Cater
authors.forename: Samuel T
authors.initials: ST
authors.lastname: Kuna
mesh_terms: D000403:Airway Resistance / Q000502:physiology; D019412:Anatomy, Cross-Sectional; D000818:Animals; D008279:Magnetic Resonance Imaging; D009765:Obesity / Q000473:pathology* / Q000503:physiopathology*; D010614:Pharynx / Q000473:pathology* / Q000503:physiopathology*; D051381:Rats; D011924:Rats, Zucker; D015656:Respiratory Mechanics / Q000502:physiology*; D013718:Tensile Strength / Q000502:physiology