0534 Balanced Co-activation of Protrudors and Rectractors is Required to Prevent Pharyngeal Obstruction During Sleep

Abstract Introduction Obstructive sleep apnea (OSA) is characterized by recurrent upper airway obstruction caused by a loss of upper airway muscle tone during sleep. Reductions in Genioglossus (GG) muscle tone, the main upper airway (UA) dilator, during sleep is thought to play a critical role in the pathogenesis of UA obstruction. Nevertheless, recent evidence suggests that lingual retractors also stabilize UA patency during sleep, leading us to hypothesize that co-activating lingual muscles can augment responses in UA patency during sleep Methods 14 apneic patients implanted with a multi-channel hypoglossal nerve stimulating system (Imthera aura 6000) underwent mid-sagittal ultrasound tongue imaging during wakefulness. Changes in tongue shape and position were characterized by measuring its vertical height and the polar dimensions between the tongue surface and genioglossus origin in the mandible (mental spine). Changes in airway patency were characterized by comparing airflow responses between stimulated and adjacent unstimulated breaths during NREM sleep. Results Two distinct morphologic responses to stimulation were observed. Anterior tongue base and hyoid bone movement (5.3 ± 0.2 to 4.2 ± 0.5 cm) with concomitant increases in tongue height (4.7 ± 0.4 to 5.3 ± 0.7 cm) resulting in only modest changes in airway patency. In contrast, when stimulation generated forward movement (5.7 ± 0.3 to 4.5 ± 0.7 cm) without any increase in height (4.6 ± 0.5 to 4.6 ± 0.9 cm), marked increases in airway patency were observed. Conclusion Lingual muscles that protrude the tongue while preserving tongue shape and prevent the tongue from bulging upward were associated with greater increases in pharyngeal patency during sleep. These morphologic differences suggest that co-stimulating lingual muscles stiffen the tongue, and prevent it from prolapsing into the pharynx during sleep. Our findings further suggest that dilating and stiffening actions of lingual protrudors and retractors can maintain UA patency during sleep. Support (If Any) Imthera Medical AHA: 16post31000017.