Genioglossal length and EMG responses to static upper airway pressures during hypercapnia in goats

Mechanoreflexes that activate genioglossus electromyogram (EMGgg) in response to negative upper airway pressure (UAP) may help defend airway patency in obstructive sleep apnea. Hypercapnia may affect mechanoreflexes by increasing EMGgg response to actively reduce genioglossus length (Lgg, measured by sonomicrometry). We hypothesized that during normocapnia, Lgg would be reduced at positive, and increased at negative UAP but hypercapnia would increase EMGgg responses to negative pressures and cause Lgg reductions. At 0, 3.5 and 7% inhaled CO₂ (balance O₂), Lgg and EMGgg were measured during static negative and positive UAP applied to the isolated upper airway in four unanesthetized goats. At 3.5 and 7% CO₂ EMGgg was significantly increased and Lgg decreased with negative pressure while EMGgg was also greater at 7 than 0% CO₂ (P<0.05). Non-significant pressure related Lgg changes were observed during normocapnia. These results suggest that hypercapnia may stimulate greater mechanoreflex EMGgg activation and consequent Lgg reduction in response to negative UAP application.