• Elizabeth C Brown, Shaokoon Cheng, David K McKenzie, Jane E Butler, Simon C Gandevia, and Lynne E Bilston.
• Neuroscience Research Australia, Barker St, Randwick, Sydney, NSW, 2031, Australia.
• Sleep. 2015 Apr 1;38(4):537-44.

Study ObjectivesThis 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.DesignControlled experimental study.SettingMedical research institute.ParticipantsPatients with OSA and age-, sex-, and BMI-matched healthy controls.MeasurementsMagnetic 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.ResultsTongue 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.ConclusionsIn 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.© 2015 Associated Professional Sleep Societies, LLC.

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