Treating Obstructive Sleep Apnea With Hypoglossal Nerve Stimulation

Arie Oliven

Disclosures

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

In This Article

Physiological Studies in Humans

Genioglossus muscle stimulation during sleep that results in genioglossus muscle contraction reduces the critical occlusion pressure of the pharynx (Pcrit).[29] Recent studies conducted under propofol anesthesia ('pharmacological sleep') provided additional physiological findings relevant to OSA: genioglossus muscle stimulation was shown to lower Pcrit when the primary site of collapse was at the level of the velopharynx as well.[30] Genioglossus muscle contraction appears to improve pharyngeal stability by reducing extrapharyngeal pressure, rather than by lowering pharyngeal compliance.[31•] Interestingly, advancement of the tongue is not mandatory, as genioglossus muscle stimulation often also enlarges the velopharynx in the lateral direction.[32] However, it is important to recruit the appropriate tongue fibers: the fan-like orientation of the genioglossus muscle fibers produces both tongue depressant and protrusive effects, and only the latter improves flow-mechanics.[33•] Therefore, more targeted stimulation would be expected to optimize the mechanical response. Independently of the site of stimulation, large differences in the response to stimulation were observed between OSA patients.[29,30,33•] These differences did not correlate with the anthropometric, polysomnographic, or cephalometric characteristics of these OSA patients. However, patients with a relatively larger tongue tended to have a larger response.[33•] Changes in length-tension relationships may affect the mechanical response to genioglossus muscle contraction, but under physiological conditions this effect appears to be minimal.[34] Also, co-activation of tongue retractors produced a similar response to that of isolated genioglossus muscle stimulation.[35] All of these physiological human studies, while confirming the feasibility and mechanical efficacy of tongue muscle stimulation, also suggested that only neurostimulation of the pure motor hypoglossus nerve, which avoids the sensation of the stimulation by sensory lingual nerve fibers, has a potential to become clinically relevant as a new treatment modality for OSA.

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