0450 Genioglossus Motor Control During Mandibular Advancement and Inspiratory Resistive Loading

Abstract Introduction High activity of the genioglossus muscle is thought to prevent/resolve upper airway collapse. The individual motor units that make up the overall genioglossal activity typically fire with one of five 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). Most experimental manipulations investigated thus far (hypoxia, hypercapnia, resistive loading and sleep onset/arousal) have largely influenced IP and IT motor units, with minimal changes in units with ET, EP and TT patterns. We hypothesized that IT/IP motor units respond to respiratory drive changes, whereas TT/EP/ET motor units will respond to manipulations of the airway anatomy. Methods Genioglossal motor units were assessed via four intramuscular electrodes in 20 healthy individuals during wakefulness. Genioglossal single motor units were quantified before and during mandibular advancement (MAD) to 80% of maximum with a myTAP device to change airway anatomy but minimally alter respiratory drive, as well as before and during inspiratory resistive loading (IRL) of 20cmH2O/l/s for 1-minute periods. Results 201 motor units were identified from 55 MAD trials and 234 motor units were identified from 58 IRL trials. Ventilation did not differ between baseline and MAD or IRL. The proportion of motor units with different patterns did not differ from baseline (EP=0.6%, ET=12.6%, IP=14.9%, IT=48%, TT=24%) to MAD (EP=0%, ET=10.2%, IP=21.1%, IT=36.7%, TT=31.9%), χ2(7)=12.0, p=.213. However, the proportion of motor units with different patterns differed from baseline (EP=0%, ET=15.4%, IP=34.6%, IT=32.4%, TT=17.6%) to IRL (EP=1.7%, ET=14.1%, IP=44.9%, IT=29.1%, TT=5.1%), χ2(7)=15.8, p=.0013. The peak firing frequency of motor units did not change during MAD (baseline=20.9±4.7Hz, MAD=21.9±5.4Hz) but increased during IRL (baseline=20.4±5.5, IRL=22.8±5.6Hz, p< 0.001). Conclusion While resistive loading increased the firing (rate and number) of inspiratory-phasic motor units as hypothesised, the firing of tonic and expiratory modulated motor units did not differ from baseline during mandibular advancement. What controls the non-respiratory/expiratory motor units of the genioglossus remains unclear. Support (if any) This work was funded by the Australian Research Council, DP170104375 and the Melbourne School of Psychological Sciences, University of Melbourne.