O058 Neural drive to the human strap muscles

Abstract Introduction Maintaining upper airway patency relies on coordinated drive to dynamically interacting muscles, including the genioglossus and strap muscles in the neck. While animal studies suggest that the sternothyroid and sternohyoid muscles have inspiratory modulation, whether human strap muscles have respiratory-related modulation is unknown. Accordingly, this study aimed to characterise the pattern and discharge rate of single motor units (SMU) of human strap muscles during quiet and stimulated breathing. Methods To date, SMU activity was recorded during quiet, increased CO₂ breathing and deep breaths in the supine position in a healthy female participant. Electromyography (EMG) activity was recorded from 5-10 sites in the right sternohyoid and sternothyroid using a monopolar needle electrode probe inserted via ultrasound guidance. Genioglossus EMG was recorded using intramuscular wire electrodes. Respiratory variables were recorded via nasal mask and pneumotachograph. SMUs were discriminated to determine their discharge pattern, timing, and firing frequency. Results Initial analysis indicates that during quiet breathing, most sternothyroid SMUs show phasic inspiratory activity, with some tonic SMUs with inspiratory modulation. There was a variable response to increased CO₂ and voluntary mediated deep breaths. No respiratory-related motor unit activity has thus far been observed in the sternohyoid. Discussion Findings from this on-going study represent the first comprehensive description of respiratory-related motor unit activity in human strap muscles. Understanding their control is crucial to advance knowledge of the pathophysiology of conditions in which upper airway patency is compromised, such as obstructive sleep apnoea, and to inform novel emerging electrical stimulation approaches targeting these muscles.