Genioglossal but not palatal muscle activity relates closely to pharyngealpressure

The stimuli controlling pharyngeal dilator muscles are poorly defined. Loca l mechanoreceptors are a leading possibility. To address this, we assessed the relationship between two dilator muscle electromyograms (EMGs, i.e., ge nioglossus [GG-an inspiratory phasic muscle], tensor palatini [TP-a tonical ly active muscle]) and potential stimuli (i.e., epiglottic pressure [Pepi], airflow [(V) over dot], and pharyngeal resistance [Rpha]). Fifteen normal subjects were studied, during wakefulness and stable non-rapid eye movement (NREM) sleep. The GGEMG and TPEMG were assessed during basal breathing and during inspiratory resistive loading (four loads, done in triplicate), whi le quantifying Pepi and choanal pressures (Pcho, Millar catheters) plus (V) over dot. There was a strong correlation between Pepi and GGEMG during wak efulness in most subjects (9 of 15 had absolute R > 0.7 [p < 0.05], group m ean R = -0.62, p < 0.05). These correlations were less robust during NREM s leep (8 of 15 absolute R > 0.6 [p < 0.05], group mean R = -0.39, ns). The s lope of the Pepi versus GGEMG relationship was greater during wakefulness t han sleep (-0.67 versus -0.39% max/cm H2O, p < 0.05). No significant correl ations were observed between TPEMG and any of the measured potential stimul i. We conclude that intrapharyngeal pressure may modulate genioglossus acti vity during wakefulness, with a fall in muscle responsiveness during sleep. The activity of the TP was not clearly influenced by any measured local st imulus either awake or asleep.