Continuous positive airway pressure remains the gold standard and first-line treatment for moderate to severe OSA. When CPAP and other medical therapies fail or are poorly adopted, surgical solutions - either standalone or in unison - can be directed to target precision therapy.
The newest of these techniques is neuromodulation of the lingual musculature, particularly by way of selective stimulation of the hypoglossal nerve, which first demonstrated success in human clinical trials in 1996.1 Upper airway stimulation (UAS) was formally FDA-approved in 2014 (Inspire Medical Systems, Inc). UAS is designed to eliminate clinically significant OSA through stimulation of the anteriorly directed branches of the hypoglossal nerve, increasing the posterior airway space in a multilevel fashion.2 Since this time, over 7,500 patients have been treated with Inspire in nine countries (United States, Germany, The Netherlands, Switzerland, Belgium, Spain, France, Italy, and Finland). Prospective, international multicenter trials have demonstrated 68% to 96% clinical efficacy in well selected individuals. This is defined as a ≥ 50% reduction in the apnea hypopnea index (AHI) to an overall AHI of ≤ 20/hour.3,4 Additionally, post-UAS analysis demonstrates subjective reduction in daytime sleepiness as reported by Epworth sleepiness scores, with improvements in sleep-related quality of life. Further, UAS reduces socially disruptive snoring with 85% of bedpartners reporting soft to no snoring at 48-month follow-up.5 The procedure has also demonstrated long-term cost benefit in the US health-care system.6
Background and pathophysiology
Oliven and colleagues7 first observed the critical finding that selective intra-muscular stimulation of the genioglossus muscle lowered airway critical closing pressure (PCrit), thereby stabilizing the pharyngeal airway. Conversely, activation of the “retrusor” musculature, namely the hyoglossus and styloglossus muscles, increased Pcrit, increasing collapsibility of the pharyngeal airway.
Therapeutic implantation requires three incisions directed to the neck, chest, and right rib space (between the 4th to 6th intercostal spaces), with an operative time of 90 minutes or less in experienced hands. The majority of patients are discharged on the day of the procedure. Morbidity remains low with minimal pain reported during recovery. The most common complication is that of temporary tongue weakness, which typically resolves within 2 to 3 weeks. While very infrequent, patients should be counseled on the risk of postoperative hematoma, which can precipitate infection and subsequent explant of the device. Average recovery time spans between 3 and 7 days with activation of the device 4 weeks after surgical implantation to allow for appropriate tissue healing and reduce the risk of dislodgement of the implanted components. In contrast to other surgical treatment options, UAS is also reversible with no underlying alteration to existing pharyngeal anatomy apart from external incisions created during the procedure.
Stimulation to titration
As the need for a multidisciplinary approach to salvage of patients failing first-line therapy for OSA continues to grow, UAS with its multilevel impact continues to be of key interest. In similar fashion to established medical therapies such as PAP and oral appliance therapy (OAT), close observation between sleep medicine specialists and the implanting surgeon during the adaptation period with attention paid to titration parameters such as stimulation duration, pulse width, amplitude, and polarity, allow optimization of response outcome.