Upper airway muscle activity in normal women: influence of hormonal status

Obstructive sleep apnea is a disorder with astrong male predominance. One possible explanation could be an effectof female hormones on pharyngeal dilator muscle activity. Therefore, we determined the level of awake genioglossus electromyogram (EMGgg) andupper airway resistance in 12 pre- and 12 postmenopausal women underbasal conditions and during the application of an inspiratory resistiveload (25 cmH₂O · l¹ · s).In addition, a subgroup of eight postmenopausal women were studied asecond time after 2 wk of combined estrogen and progesterone replacement in standard doses. Peak phasic and tonic genioglossus activity, expressed as a percentage of maximum, were highest in theluteal phase of the menstrual cycle (phasic 23.9 ± 3.8%, tonic 10.2 ± 1.0%), followed by the follicular phase (phasic 15.5 ± 2.2%, tonic 7.3 ± 0.8%), and were lowest in the postmenopausal group (phasic 11.3 ± 1.6%, tonic of 5.0 ± 0.6), whereas upper airway resistance did not differ. There was a weak but significant positive correlation between progesterone levels and both peak phasic(P < 0.05) and tonic(P < 0.01) EMGgg. Finally, there was a significant increase in EMGgg in the postmenopausal group restudied after hormone therapy. In conclusion, female hormones (possibly progesterone) have a substantial impact on upper airway dilator muscleactivity.