RM Popovic and DP White
University of Colorado Health Sciences Center, Denver Veterans Administration Medical Center 80220, USA.

Obstructive sleep apnea is generally recognized as more common in men than in women. This could relate to gender differences in either ventilatory control mechanisms or the structure and function of the pharyngeal airway. Most studies suggest that women have a structurally smaller pharyngeal airway than men, which would likely predispose rather than protect them from airway collapse. However, pharyngeal airway patency is actually a dynamic interaction between anatomy and pharyngeal muscle activity. We therefore hypothesized that females may have increased pharyngeal dilator muscle activity, thereby protecting them from airway collapse during sleep. To test this hypothesis, we compared genioglossal EMG (GG-EMG, measured as a percentage of maximal muscle activity) and upper airway resistance in 22 healthy subjects, 11 males and 11 females, during wakefulness. No significant difference in pharyngeal resistance could be found between the genders. However, inspiratory peak phasic and expiratory tonic GG-EMG activity were both significantly greater in females (GG-EMG peak phasic; 24.3 +/- 3.8 versus 13.1 +/- 4.5% of maximum, p < 0.02; GG-EMG tonic; 12.2 +/- 2.8 versus 4.7 +/- 1.2% of maximum, p < 0.01). In addition, females demonstrated a significant EMG response to inspiratory loading that was not observed in men. We conclude that women have, under basal conditions during wakefulness, augmented genioglossal muscle activity compared with men. To the extent that this augmented muscle activity is maintained across states, the female airway may be more stable and less collapsible.

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