Tongue Morphology and Posterior Airway Space as Predictors of Response in Patientswith Hypoglossal Nerve Stimulation Therapy

Hypoglossal nerve stimulation (HNS) plays an increasingly important role in managing patients with obstructive sleep apnea (OSA) who do not tolerate CPAP therapy and are not eligible for other alternative treatment options, such as mandibular advancement devices or positional therapy. The posterior upper airway space dimensions are crucial in managing patients with HNS in the patient selection process and therapy control. The lateral collapse of the upper airway is of crucial importance. Lateral collapse at the palatal level and of the oropharyngeal walls is a well-established negative predictive factor for therapeutic success. Patients with complete concentric collapse at the palatal level (pCCC) in drug-induced sedation endoscopy (DISE) must be excluded from the implantation of HNS, which is cumbersome and invasive. Endoscopy has the inherent limitation that only one level can be observed at a given time, and assessment is possibly hampered by phlegm.

During activation and titration of HNS, tongue protrusion is observed in the awake patient. However, this method does not allow for assessing the opening of the retroglossal (RG) and retropalatal (RP) airway space, which is the ultimate therapeutic goal. Insufficient opening of the airway is the reason for non-responders with HNS. Insufficient upper airway opening can be either at the retropalatal or retroglossal level. The study aims to identify insufficient airway openings better using sub-mental ultrasonography. Sub-mental standardized and orientated ultrasonography offers a quantitative, reproducible way of assessing transverse upper airway dimensions and anatomic features of the upper airway in a rapid and non-invasive manner. In addition, anatomic characteristics of the airway's adjacent tissue, such as the size and shape of the tongue, may also have an impact on the effectiveness of HNS. Tongue morphology and posterior airway space assessment could be used in preoperative evaluation and during therapeutic titration of HNS. The clinical routine could be included tongue morphology and posterior airway space assessment without additional patient risks. However, the clinical value of assessing posterior airway space and tongue morphology in patients with HNS is yet unknown.