Genioglossal activity at rest and in response to a brief hypoxic stimulus in healthy men and women

Obstructive sleep apnea is more common in men than in women for reasons that are not clearly understood. A difference in respiratory neural control of upper airway dilator muscles has been suggested as a possible reason for this difference. To investigate this further, we have compared three aspects of upper airway dilator muscle function in healthy men and women: 1 ) resting inspiratory genioglossus EMG (EMGgg) activity, 2) the respiratory EMGgg afterdischarge following a brief hypoxic stimulus, and 3) the relationship between the EMGgg and pharyngeal airway pressure. METHODS: Minute ventilation, epiglottic pressure, genioglossus and diaphragm EMGs were measured in 24 subjects ( 12 men, 12 women in the luteal menstrual phase) while lying supine awake. Every 7-8 minutes for 2 hours subjects were exposed to 45-second periods of hypoxia (9% 0: in N2) that were abruptly terminated with one breath of 100% 02. End tidal C02 was controlled during and after hypoxia by bleeding C0: into the inspirate. Ventilator)', diaphragmatic and genioglossal EMGs were measured before, during and after the hypoxic intervention and correlations made between epiglottic pressure and EMGgg. Means ±SEM are presented. p0.05 significant. RESULTS: 117 trials with satisfactory end tidal CO-, control and no sighs or swallows are reported. There was no gender difference in the resting level of peak inspiratory EMGgg (3.7 ±0,8 women, 3.2 ±0.6 men, % maximal activity). Repeated measures ANOVAs showed no gender or gender by time interaction effect between men and women in minute ventilation, genioglossal or diaphragmatic activity during and after the hypoxic stimulus. The relationship between epiglottic pressure and EMGgg was not different between men (slope; -0.63 ±0.20) and women (slope; -0.69 ± 0.33). CONCLUSIONS: These results do not provide support for the hypothesis that the higher prevalence of OSA in men is related to an underlying gender difference in respiratory neural control of upper airway dilator muscles.