The effect of hypoxic depression on genioglossal muscle activity in healthy subjects and obstructive sleep apnea patients.

We investigated whether selective depression of the genioglossus muscle (GG) activity could be associated with hypoxic ventilatory depression, which is developed in the late phase of the biphasic ventilatory response during sustained hypoxia. Eleven control subjects and 10 patients with obstructive sleep apnea syndrome (OSAS) were examined by an isocapnic sustained hypoxia test for 20 minutes. Ventilatory parameters and electromyographic (EMG) activities were recorded from GG (EMGGG) and diaphragm (EMGDIA). Hypoxic depression in minute ventilation (V1) and EMGDIA occurred when compared between the peak value and the value at late period in both groups. On the contrary, depression in EMGGG was not observed in controls (86% of the peak value), whereas EMGGG was strikingly depressed in OSAS (39% of the peak value). We conclude that sustained hypoxia reduces the activity of GG in OSAS, but not in control subjects. These data suggest that the lack of a compensatory response of GG to sustained hypoxia is possibly responsible for the pathogenesis of OSA.