Neurophysiologic tongue protrusion characteristics$ in obstructive sleep apnea: A comparative study

Area of Science:

• Physiology
• Neurology
• Sleep Medicine

Background:

• Upper airway muscle function is crucial for maintaining airway patency during sleep.
• Alterations in tongue muscle properties are hypothesized to contribute to obstructive sleep apnea (OSA).
• Previous studies on tongue muscle mechanics in OSA patients have produced inconsistent findings.

Purpose of the Study:

• To objectively evaluate tongue muscle mechanics in OSA patients using non-volitional electrical stimulation.
• To compare tongue protrusion force and fatigability between OSA patients and healthy controls.
• To investigate potential differences in muscle fiber characteristics and coordination.

Main Methods:

• Surface electrical stimulation of the genioglossus (GG) muscle was employed to assess non-volitional tongue protrusion force.
• Volitional tongue protrusion force was also measured for comparison.
• Muscle fatigability was assessed during volitional testing and varying frequencies of electrical stimulation.
• Twitch contraction and half-relaxation times were analyzed.

Main Results:

• OSA patients demonstrated significantly lower tongue protrusion force, both volitional and stimulated, compared to controls.
• Stimulated force was consistently lower than volitional force but strongly correlated (r = 0.62, p < 0.001).
• Increased tongue muscle fatigability was observed in OSA patients during high-frequency stimulation, but not during low-frequency stimulation or volitional testing.

Conclusions:

• Maximal tongue protrusion force is reduced in OSA patients, despite seemingly similar muscle fiber composition.
• Methodology for assessing tongue muscle function, particularly the testing mode, is critical for uncovering deficits.
• Increased fatigability under high-frequency stimulation suggests a potential tongue muscle neuropathy in OSA.
• Coordination deficits may play a role in OSA pathophysiology.