Control of epiglottic position in dogs: role of negative upper airway pressure.

We investigated the influence of negative upper airway pressure (NUAP) on hyoepiglotticus and genioglossus muscle electromyographic (EMG) activity in anaesthetised (sodium pentobarbitone/ chloralose) dogs breathing via a tracheostomy. Changes in pressure were not transmitted through the entire upper airway, thus confirming airway occlusion during NUAP. When NUAP was applied at the larynx, peak inspiratory and tonic EMG activity of the genioglossus and HE both increased significantly (p < 0.05) and reached a plateau at NUAP of -10 to -20 cmH2O. Nasal NUAP at any level failed to influence either genioglossus or HE EMG activity. Following bilateral section of the internal branches of the superior laryngeal nerves (SLNin), resting levels of HE and genioglossus EMG activity decreased to virtually zero. Moreover, NUAP applied at the larynx now failed to recruit EMG activity for either muscle. These findings suggest active control of epiglottic position in dogs during NUAP.