Local reflex mechanisms: Influence on basal genioglossal muscle activation in normal subjects

Study Objectives: To define the influence of topical nasopharyngeal anesthesia on genioglossal EMG responsiveness to both negative pressure and basal muscle activity. The effects on airway mechanics (resistance and collapsibility) were also determined. Participants: 18 normal adult subjects (9 males and 9 premenopausal females) Design and Measurements: Genioglossal EMG (GG EMG) was measured with intramuscular electrodes. Basal phasic and tonic GG EMG were defined, in addition to the muscle response to multiple brief applications of negative airway pressure (-10 to 12 cm H₂O). Airflow resistance (at 0.2 L/second and peak flow) plus airway collapsibility were also determined. All measurements were completed with and without dense nasopharyngeal anesthesia (lidocaine). Results: Following nasopharyngeal anesthesia, peak GG EMG response to negative pressure fell from 28.1±4.3 (SE) to 19.6±3.4% of maximum (p<0.01). This was associated with a significant fall in both peak phasic and tonic GG EMG under basal conditions (phasic: 20.2 ± 3.2 to 15.9±2.7% of maximum, tonic: 13.9±2.5 to 9.8±1.8% of maximum). Falling muscle activity led to a trend of rising airflow resistance and increasing airway collapsibility. Conclusions: Local, topical receptor mechanisms located in the nasopharynx importantly modulate upper airway dilator muscle activity in humans during normal tidal breathing. Therefore, the mechanisms exist for the airway to respond to local events which would tend to compromise airway patency.