P039 Genioglossus motor control during mandibular advancement.

INTRODUCTION: High genioglossus muscle activity is thought to prevent/resolve upper airway collapse. Overall genioglossal activity results from the simultaneous firing of many motor units (MUs) which typically have one of 5 firing patterns: active only (IP) or at higher frequency (IT) during inspiration; active only (EP) or at higher frequency during expiration (ET); and constantly active without respiratory modulation (TT). To date, most experimental manipulations tested (e.g. hypoxia, hypercapnia, resistive loading) have influenced IP and IT MUs, with minimal changes in ET, EP and TT MUs. We hypothesized that IT/IP MUs respond to respiratory drive, whereas TT/EP/ET MUs will change in response to airway anatomical manipulations. METHODS: The number and firing frequencies of genioglossal MUs were assessed with intramuscular electrodes in healthy individuals during wakefulness, before and during mandibular advancement (MAD) to 80% of maximum with an myTAP device, to change airway anatomy but minimally alter respiratory drive. RESULTS: 201 MUs were identified from 55 trials in 14 participants. Ventilation did not differ between baseline and MAD. At baseline, 175 MUs were active: EP=0.6%, ET=12.6%, IP=14.9%, IT=48%, TT=24%. During MAD, 35 MUs ceased firing, but an additional 26 MUs began firing, with the resulting MUs proportions not differing from baseline: EP=0%, ET=10.2%, IP=21.1%, IT=36.7%, TT=31.9%, χ2(9)=12.0, p=.213. The mean firing frequency of MUs did not change during MAD (baseline=20.9±4.7Hz, MAD=21.9±5.4Hz). DISCUSSION: Contrary to the hypothesis, the firing patterns of genioglossal MUs did not differ from baseline during mandibular advancement. What controls the non-respiratory/expiratory MUs of the genioglossus remains unclear.