Effects of chronic episodic hypoxia on rat upper airway muscle contractile properties and fiber-type distribution.
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.


METHODS
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.
McGuire
Michelle
M
Department of Physiology, Royal College of Surgeons in Ireland, St. Stephen's Green, Dublin, Ireland.
MacDermott
Mary
M
Bradford
Aidan
A
D000818:Animals; D046508:Culture Techniques; D006801:Humans; D000860:Hypoxia / Q000473:pathology / Q000503:physiopathology*; D007537:Isometric Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000473:pathology / Q000502:physiology*; D009130:Muscle, Smooth / Q000473:pathology / Q000503:physiopathology*; D010609:Pharyngeal Muscles / Q000473:pathology / Q000503:physiopathology; D010614:Pharynx / Q000473:pathology / Q000503:physiopathology; D051381:Rats; D017208:Rats, Wistar; D020181:Sleep Apnea, Obstructive / Q000473:pathology / Q000503:physiopathology