LOCAL REFLEX MECHANISMS - INFLUENCE ON BASAL GENIOGLOSSAL MUSCLE ACTIVATION IN NORMAL SUBJECTS

Study Objectives: To define the influence of topical nasopharyngeal an esthesia 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 adu lt subjects (9 males and 9 premenopausal females) Design and Measureme nts: Genioglossal EMG (GG EMG) was measured with intramuscular electro des. Basal phasic and tonic GG EMG were defined, in addition to the mu scle response to multiple brief applications of negative airway pressu re (-10 to 12 cm H2O). Airflow resistance (at 0.2 L/second and peak fl ow) plus airway collapsibility were also determined. All measurements were completed with and without dense nasopharyngeal anesthesia (lidoc aine). Results: Following nasopharyngeal anesthesia, peak GG EMG respo nse to negative pressure fell from 28.1+/-4.3 (SE) to 19.6+/-3.4% of m aximum (p<0.01). This was associated with a significant fall in both p eak 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 rec eptor mechanisms located in the nasopharynx importantly modulate upper airway dilator muscle activity in humans during normal tidal breathin g. Therefore, the mechanisms exist for the airway to respond to local events which would tend to compromise airway patency.