Dose-dependent effects of mandibular protrusion on genioglossus activity in sleep apnoea

Abstract

To the Editors: In individuals with a compromised upper airway, the activity of the genioglossus (GG) muscle is augmented to maintain upper airway patency during wakefulness 1. However, sleep greatly suppresses GG muscle activity, which may lead to partial or complete upper airway collapse in patients with obstructive sleep apnoea (OSA). Mandibular-advancing oral appliances are currently accepted as one promising approach to the treatment of mild-to-moderate OSA 2, 3. Although enlargement of the upper airway at multiple levels may be important for producing a clinical effect, the contributions of oral appliances to functional aspects, in terms of GG muscle activity, have hardly been documented. If mandibular advancement increased the electromyographic activity of the GG muscle (GGEMG), this effect should help to maintain the patency of the airway, since the activation of GGEMG could stiffen the compliant airway wall 4. In contrast, if we consider that mandibular advancement increases the cross-sectional area and decreases the propensity for upper airway occlusion, it would be reasonable to hypothesise that a larger, less collapsible upper airway could improve airflow dynamics, which would require less GGEMG 5. Accordingly, we investigated the effects of mandibular advancement by an experimental oral appliance on GGEMG and the severity of OSA during sleep. The study protocol was approved by the Clinical Research Ethics Board at the University of British Columbia (UBC), Vancouver, Canada. A 54-yr-old male patient with severe OSA (body mass index 31.2 kg·m−2 and apnoea/hypopnoea index (AHI) 30.3 events·hr−1) who showed a resolution of symptoms, including daytime sleepiness, snoring and/or apnoea, after complete titration of the oral appliance (Klearway™; Great Lakes Orthodontics, Tonawanda, NY, USA) was recruited into the study. The patient had used the oral appliance for a period of 4 months prior to the …