Response of genioglossus EMG activity to passive tilt in men.

Increased blood pressure (BP) leads to inhibition of respiratory activity of hypoglossal nerve in anesthetized cats, implying that arterial baroreceptor activity may inhibit upper airway motor outputs. We examined the effect of passive tilt on upper airway muscle activity in men under the assumption that changes in degree of tilt would change local pressure at the carotid baroreceptors. We also examined the possibility that inhibition of upper airway muscle activity occurred secondary to a decrease in level of arousal. In seven normal awake adult males, we measured electromyogram activity of the genioglossus (EMGge), electroencephalogram (EEG), electrocardiogram, ventilation, end-tidal fractional concentration of CO2, and BP while the subject was on a tilt table wearing inflatable antishock pants. Three tilt table positions were used: 60 degrees head-up (60 degrees increases), supine (S), and 30 degrees head-down (30 degrees decreases), with pants either deflated (P-) or inflated (P+) to 40 mmHg. During P-, moving the subject from 60 degrees increases to S to 30 degrees decreases positions resulted in steady-state heart rates of 94.8 +/- 1.7, 66.9 +/- 0.7, and 68.9 +/- 0.8 beats/min and EMGge activities of 54.4 +/- 4.4, 37.7 +/- 2.0, and 31.5 +/- 2.4% of maximum, respectively. During P+, changes in heart rate were similar but significantly reduced from P-, and positional changes in EMGge were eliminated. The level of arousal was unchanged. The transient response of EMGge to tilt was biphasic: when moving from upright to supine position, there was a rapid increase in activity during the tilt maneuver followed by a progressive decline.(ABSTRACT TRUNCATED AT 250 WORDS)