(1317) Quantitative Measurement of Hypoglossal Nerve Stimulation Efficacy During Drug-Induced Sleep Endoscopy

Introduction: Obstructive sleep apnea (OSA) is characterized by recurrent episodes of airway obstruction leading to repeated oxyhemoglobin desaturation and arousals. Hypoglossal nerve stimulation (HGNS) has been shown to effectively treat a subset of OSA patients by increasing genioglossal tone thereby improving pharyngeal patency. In this preliminary study, a platform was created to simultaneously quantify genioglossus motion, airway cross-sectional area, and maximal inspiratory flow.

Methods: To examine inter-relationships between changes in tongue morphology, velopharyngeal cross-sectional area, and airway patency, we characterized responses in these parameters to HGNS within three responders. Specifically, (1) ultrasound was used to measure tongue shape and position at polar coordinates 0°, 30° 45°, 60°, 75°, and 90° from the mandibular-hyoid plane, (2) endoscopic analysis allowed for quantification of airway cross-sectional area using the diameter of the catheter as a reference to convert pixels to millimeters, and (3) maximal volumetric flow (Vimax) for 5 representative breaths on and off stimulation were measured.

Results: Participants were elderly (64 ± 4 yrs, mean ± SD), overweight (BMI 29 ± 3 kg/m2), and had moderate-severe OSA (AHI 28 ± 17 events/hour). Analysis of 30 breaths revealed that forward movement of the tongue (difference of 8.7 mm at 30°, p < 0.001) without increases in height (difference of 2 mm at 90°, p = 0.2) confers substantial increases in Vimax (3.13 to 8.53 L/min, p < 0.001) and cross-sectional area (9.03 to 53.78 mm2, p = 0.01).

Conclusions: Synchronous responses in tongue position, luminal cross-sectional area, and maximal flow (Vimax) during HGNS, point to tongue-driven causal mechanisms for airway obstruction. Considerable variability in apnea responses to HGNS may be attributed to differences in tongue movement and shape.