Effect of wake-sleep transitions and rapid eye movement sleep on pharyngeal muscle response to negative pressure in humans

1. Genioglossus (GG) activation in response to upper airway negative pressu re may be an important mechanism in the maintenance of airway patency This reflex occurs during wakefulness but is diminished during stable non-rapid eye movement (NREM) sleep. Since obstructive events occur more commonly at wake-sleep transitions and during rapid eye movement (REM) sleep than durin g stable NREM sleep, we assessed the GG reflex during these two vulnerable states. 2. Seventeen healthy adults were studied throughout one evening and overnig ht. Electroencephalograms (EEGs), electro-oculograms (EOGs), submental elec tromyogram (EMG), GG EMG; (intramuscular electrodes), and choanal plus epig lottic pressures were recorded. The GG; reflex response to pulses of -8 cmH (2)O choanal pressure applied via nose mask during early inspiration was qu antified repeatedly during: relaxed wakefulness, within five breaths of wak e-sleep transition (EEG alpha-theta transition) and during REM sleep. Only trials without EEG arousal were analysed, resulting in data from 14 subject s during sleep onset and 10 subjects during REM sleep(overall, 174-481 tria ls per state). 3. During wakefulness there was brisk GG reflex activation in response to n egative pressure (amplitude: +78.5 +/- 28.3% baseline (mean +/- S.E.M); lat ency to maximal response: 177 +/- 16 ms). 4. At sleep onset, although there was marked variability among individuals, there was no significant reduction in the magnitude of the GG reflex for t he group as a whole (amplitude: +33.2 +/- 8.2% baseline; latency: 159 +/- 1 5 ms). 5. In contrast, during REM sleep there was a reduction of GG reflex (amplit ude: -12.6 +/- 8.3% baseline (P = 0.017 vs. awake); latency: 160 +/- 10 ms (n.s. vs. awake)) and greater airway collapsibility during the applied pres sures (P = 0.043 vs. awake). 6. We conclude that there was no systematic reduction in the Oa reflex to n egative pressure at sleep onset. Nonetheless, it remains possible that stee p-deprived normal subjects and patients with sleep apnoea could react diffe rently. 7. The apparent inhibition of the GG reflex during REM sleep may help expla in why the upper airway is vulnerable to collapse during this state.