OBJECTIVE: Contraction of upper airway (UA) muscles such as the geniohyoids and sternohyoids dilates and/or stabilizes the UA, thereby maintaining its patency. Obstructive sleep apnea (OSA) is caused by episodes of UA collapse, and this results in chronic episodic hypoxia. Chronic continuous hypoxia affects skeletal muscle structure and function, but the effects of chronic episodic hypoxia on UA muscle structure and function are unknown. DESIGN: Rats were exposed to alternating periods of hypoxia and normoxia twice per minute for 8 h/d for 5 weeks in order to mimic the intermittent hypoxia of OSA in humans. Isometric contractile properties were determined using strips of isolated geniohyoid and sternohyoid muscles in physiologic saline solution at 30 degrees C. Fiber-type distribution was determined using adenosine triphosphatase staining. RESULTS: Chronic episodic hypoxia had no significant effect on twitch or tetanic tension, twitch/tetanic tension ratio, contractile kinetics, tension-frequency relationship, or fiber-type distribution for either the sternohyoid or geniohyoid muscle. However, chronic episodic hypoxia did significantly increase sternohyoid and geniohyoid fatigue and reduced recovery from fatigue. CONCLUSIONS: Chronic episodic hypoxia increases UA muscle fatigue, an effect that may compromise the maintenance of UA patency.
OBJECTIVE: Contraction of upper airway (UA) muscles such as the geniohyoids and sternohyoids dilates and/or stabilizes the UA, thereby maintaining its patency. Obstructive sleep apnea (OSA) is caused by episodes of UA collapse, and this results in chronic episodic hypoxia. Chronic continuous hypoxia affects skeletal muscle structure and function, but the effects of chronic episodic hypoxia on UA muscle structure and function are unknown. DESIGN:Rats were exposed to alternating periods of hypoxia and normoxia twice per minute for 8 h/d for 5 weeks in order to mimic the intermittent hypoxia of OSA in humans. Isometric contractile properties were determined using strips of isolated geniohyoid and sternohyoid muscles in physiologic saline solution at 30 degrees C. Fiber-type distribution was determined using adenosine triphosphatase staining. RESULTS: Chronic episodic hypoxia had no significant effect on twitch or tetanic tension, twitch/tetanic tension ratio, contractile kinetics, tension-frequency relationship, or fiber-type distribution for either the sternohyoid or geniohyoid muscle. However, chronic episodic hypoxia did significantly increase sternohyoid and geniohyoid fatigue and reduced recovery from fatigue. CONCLUSIONS: Chronic episodic hypoxia increases UA muscle fatigue, an effect that may compromise the maintenance of UA patency.
Authors: Andrew M Kim; Brendan T Keenan; Nicholas Jackson; Eugenia L Chan; Bethany Staley; Drew A Torigian; Abass Alavi; Richard J Schwab Journal: Am J Respir Crit Care Med Date: 2014-06-01 Impact factor: 21.405
Authors: Robert Williams; Paul Lemaire; Philip Lewis; Fiona B McDonald; Eric Lucking; Sean Hogan; David Sheehan; Vincent Healy; Ken D O'Halloran Journal: Front Physiol Date: 2015-01-30 Impact factor: 4.566