Acute upper airway muscle and inspiratory flow responses to transcranial magnetic stimulation during sleep in apnoeic patients

Abstract

New Findings: • What is the central question of this study? Peripheral hypoglossal nerve stimulation is a novel therapeutic approach aimed at recruiting lingual muscles electrically and thus relieving pharyngeal airflow obstruction during sleep but the effects of corticomotor stimulation of upper airway muscles during sleep are unknown. • What is the main finding and its importance? Using transcranial magnetic stimulation, we show that corticobulbar excitability of the submental muscles is decreased during sleep in apnoeic patients. Furthermore, we demonstrate that transcranial magnetic stimulation briefly recruits submental muscles and increases maximal inspiratory flow as well as the inspiratory volume of flow-limited respiratory cycles without arousing patients from sleep. We suggest that this central neurostimulation approach is capable of improving upper airway mechanics in sleep apnoea patients. Transcranial magnetic stimulation (TMS) can activate the corticobulbar system and briefly recruit upper airway dilator muscles, improving the inspiratory airflow dynamics of flow-limited respiratory cycles during sleep. The purpose of this investigation was to quantify the effects of TMS-induced twitches applied during sleep on flow-limited respiratory cycles in 14 obstructive sleep apnoea patients. Submental muscle motor threshold (SUBMT) and motor-evoked potential (SUBMEP) were examined during wakefulness and sleep. The TMS-induced twitches were applied during stable non-rapid eye movement (NREM) sleep, during non-consecutive flow-limited respiratory cycles at the beginning of inspiration, with intensities varying from sleep SUBMT up to maximal stimulation without arousal. Maximal inspiratory flow, inspiratory volume, shifts of electroencephalogram frequency and pulse rate variability were assessed. Cortical and/or autonomic arousal after TMS was observed in only 13.8% of all twitches applied. The SUBMT increased during NREM sleep (wakefulness, 24.8 ± 9.3%; and NREM sleep, 28.3 ± 9.5%; P= 0.003). Augmenting stimulator output from SUBMT to maximal stimulation before arousal enhanced SUBMEP peak-to-peak amplitude (from 0.09 ± 0.05 to 0.4 ± 0.3 mV; P= 0.005) with a concomitant rise in maximal inspiratory flow (from 376.2 ± 107.9 to 411.9 ± 109.3 ml s-1; P= 0.008) and inspiratory volume (from 594.8 ± 189.2 to 663.7 ± 203.1 ml; P= 0.001) in all but one patient. Corticobulbar excitability of submental muscles decreases during NREM sleep. Brief recruitment of submental muscles with TMS during sleep improves upper airway mechanics without arousing patients from sleep. © 2013 The Physiological Society.