title: Tongue stiffness is lower in patients with obstructive sleep apnea during wakefulness compared with matched control subjects.
abstract: OBJECTIVE
  This study aimed to determine whether tongue stiffness (shear modulus) in patients with obstructive sleep apnea (OSA) is different for controls matched for age, sex, and body mass index (BMI), and to investigate the effect of continuous positive airway pressure (CPAP) on stiffness.
  
  
  METHODS
  Controlled experimental study.
  
  
  METHODS
  Medical research institute.
  
  
  METHODS
  Patients with OSA and age-, sex-, and BMI-matched healthy controls.
  
  
  METHODS
  Magnetic resonance elastography was performed in nine patients with OSA (apnea-hypopnea index (AHI) > 15 events/h) and seven controls (AHI < 10 events/h) matched for age, sex, and BMI. Six of these OSA subjects were also scanned while 10 cmH2O CPAP was applied. Mean isotropic shear modulus and anisotropic shear moduli parallel and perpendicular to the muscle fascicles in the tongue were calculated.
  
  
  RESULTS
  Tongue shear modulus in patients with OSA was lower than that in matched controls (2.68 ± 0.35 (mean ± standard deviation) kPa versus 2.98 ± 0.44 kPa, P < 0.001). Shear modulus decreased with increasing AHI (R = -0.496, P = 0.043), but not age, BMI, or percentage tongue fat. Anisotropic analysis revealed that reduction in stiffness was greatest parallel to the muscle fibers. CPAP had no significant effect on tongue shear modulus.
  
  
  CONCLUSIONS
  In awake subjects with obstructive sleep apnea, the tongue is less stiff than in similar healthy subjects and this difference occurs in the muscle fiber direction. CPAP did not significantly reduce tongue stiffness. Thus, any change in neural drive to genioglossus during wakefulness is insufficient to restore normal tongue stiffness.
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick, Sydney, NSW, 2031, Australia.|Prince of Wales Clinical School, University of New South Wales, Australia.
authors.forename: Elizabeth C
authors.initials: EC
authors.lastname: Brown
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick, Sydney, NSW, 2031, Australia.|Department of Engineering, Macquarie University, New South Wales, Australia.|School of Medical Sciences, University of New South Wales, Australia.
authors.forename: Shaokoon
authors.initials: S
authors.lastname: Cheng
authors.affiliation: Prince of Wales Clinical School, University of New South Wales, Australia.|Prince of Wales Hospital, Sydney, Australia.
authors.forename: David K
authors.initials: DK
authors.lastname: McKenzie
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick, Sydney, NSW, 2031, Australia.|School of Medical Sciences, University of New South Wales, Australia.
authors.forename: Jane E
authors.initials: JE
authors.lastname: Butler
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick, Sydney, NSW, 2031, Australia.|Prince of Wales Clinical School, University of New South Wales, Australia.
authors.forename: Simon C
authors.initials: SC
authors.lastname: Gandevia
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick, Sydney, NSW, 2031, Australia.|Prince of Wales Clinical School, University of New South Wales, Australia.
authors.forename: Lynne E
authors.initials: LE
authors.lastname: Bilston
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology / Q000502:physiology; D015992:Body Mass Index; D016022:Case-Control Studies; D045422:Continuous Positive Airway Pressure; D055119:Elastic Modulus; D054459:Elasticity Imaging Techniques; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology / Q000503:physiopathology; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology* / Q000628:therapy; D014059:Tongue / Q000033:anatomy & histology* / Q000502:physiology / Q000503:physiopathology*; D014851:Wakefulness / Q000502:physiology*
keywords: collapsibility; elastography; obstructive sleep apnea