Treating Obstructive Sleep Apnea With Hypoglossal Nerve Stimulation

Arie Oliven

Disclosures

Curr Opin Pulm Med. 2011;17(6):419-424. 

In This Article

Recent Ongoing Phase II Hypoglossus Nerve Stimulation Studies

Despite the positive results of the phase I feasibility study, it took more than 10 years before improved stimulation systems were developed and new studies were initiated. In 2009, two investigator groups started multisite studies, and a third group joined a year later. The new systems remained basically similar, with the exception of the respiratory sensor, which no longer depends on intrathoracic pressure (Fig. 1). At the time of this writing, interim results of these ongoing studies have been presented at the 2011 American Thoracic Society International Conference in Denver, Colorado. More than 60 patients had received the new devices in the USA, Europe, Israel, and Australia. Eastwood et al.[38••] reported their findings in 21 individuals (14 men) implanted with a novel HGNS (Apnex Medical Inc., St Paul, Minnesota, USA) and followed for 6 months. These investigators selected patients with predominantly obstructive hypopneas and used sensors that identified inspiration by changes in thoracic impedance. Seventy five per cent of their patients experienced greater than 50% decrease in AHI; the mean_SD AHI decreased from 43.1±17.5 to 16.3±9.1 events/h, associated with significant reduction in desaturation events and improvement in Epworth Sleepiness Scale and Functional Outcomes of Sleep Questionnaire scores. Two adverse events (stimulator pocket infection and electrode dislodgement) required surgical intervention but resolved without sequelae. Well synchronized stimulations increased inspiratory flow by 15.2±2.4 l/min.[39] Badr et al.[40••] reported their results with the Inspire system (Inspire Medical Systems, Minneapolis, Minnesota, USA), a modified and improved version of the original phase I system, now using a sensor that monitors respiratory movements. The first 22 patients enrolled had a wide range of BMI and AHI, and only eight of them were considered responders. Based on findings obtained in this first group, new selection criteria and electrode placement site were introduced. In a second group of nine individuals, all but one showed substantial improvement, with a reduction in AHI for this group from 39±9 to 12±13 events/h. The new Inspire device provided long-term safety, stability, and functional reliability over a follow-up period of more than 2 years. These results prompted a phase III study: the Stimulation Therapy for Apnea Reduction, or STAR trial. Rodenstein et al.[41••] reported their results on 11 OSA patients implanted with an original system (aura6000; ImThera Medical, SanDiego,California,USA).This device uses a silicone cuff electrode housing six independent contacts surrounding the hypoglossus nerve. This approach, although requiring elaborate titration of stimulation during wakefulness and sleep, enables a continuous ('tonic') hypoglossus nerve stimulation without the need to synchronize stimulation with the respiratory cycle. Partial unilateral tongue paresis lasting 2–3 months occurred in two participants. AHI decreased significantly from 47.4±16.9 to 19.4±12.6 events/h, associated with a corresponding decrease in desaturations.

Figure 1.

Schematic presentation of the implantable hypoglossus nerve stimulation system, designed to contract the tongue muscles during inspiration
Tetanic stimulations to the hypoglossus nerve lasting 1–2 s are applied by a pacemaker-like device, triggered by a respiratory sensor so as to be synchronized to inspiration

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