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Obstructive sleep apnea (OSA) is characterized by recurrent upper airway obstruction during sleep. Individuals with OSA tend to be obese, snore at night and have excessive day time sleepiness. The airway obstruction is secondary to sleep mediated hypotonia of the peri pharyngeal structures leading to repeated pharyngeal obstruction. The morbidity associated with this disorder is significant with increased prevalence of diabetes, hypertension, stroke and cardiac diseases in OSA patients. The cause of this increased prevalence is attributed to chronic stress and inflammation caused by recurrent hypoxia-reoxygenation cycles in sleep apnea.

Currently CPAP (Continuous Positive Airway Pressure) is the most widely used and effective treatment for obstructive sleep apnea. Other modalities include oral appliances and surgery which may be useful for some select individuals with OSA. Hypoglossal nerve stimulation is one of the newer modalities that are being developed for the treatment of OSA.

Hypoglossal nerve is one of the cranial nerves (12th). It supplies motor fibres to all of the muscles of the tongue, except the palatoglossus muscle. In hypoglossal nerve stimulation, subcutaneously placed pulse generator stimulates the hypoglossal nerve through electrodes. This stimulation leads to increase in pharyngeal muscle tone and dilatation of the pharynx. Previous studies have shown reduction in apnea-hypopnea index (a parameter for assessment of OSA), increased air flow and increased oxygenation during sleep. A recent study showed that 75% of patients enrolled in a trial had 50% drop in apnea-hypopnea index. But large difference in response to stimulation was noted and the reasons for the varied responses are unclear as of now. In one of the studies, patients with relatively larger tongue had better response to hypoglossal stimulation.

The hypoglossal stimulation is generally considered to be safe. The adverse events reported include stimulator pocket infection, electrode dislodgement, stimulator malfunction leading to premature removal and temporary unilateral tongue paresis.

Though there is a drop in apnea hypopnea index (AHI), it doesn’t completely normalize the index and hence patient may continue to have apneic events. It may reduce severe apnea to moderate or mild apnea. Whether hypoglossal stimulation can be used as a single definite modality without CPAP is unclear at present. Improvement in technology from the current unilateral hypoglossal stimulation to bilateral hypoglossal stimulation can increase the mechanical efficiency.

The results so far suggest that hypoglossal stimulation may be useful in carefully selected population. Stimulation Therapy for Apnea Reduction (STAR Trial) is an ongoing phase 3 study and the results are expected to further define the role of hypoglossal stimulation in OSA management.

Reference
http://journals.lww.com/co-pulmonarymedicine/Abstract/2011/11000/Treating_obstructive_sleep_apnea_with_hypoglossal.5.aspx