The central motor conductivity of genioglossus in obstructive sleep apnoea

During wakefulness, the electromyography (EMG) activities of upper airway dilator muscles are higher in OSA syndrome (OSAS) patients than those in normal subjects. This is believed to be related to central compensatory mechanisms. This study aimed to assess the central motor conductivity of genioglossus (GG) during wakefulness and to evaluate the compensatory site in OSAS patients.

Twelve OSAS patients and 12 normal subjects were recruited to record motor evoked potential (MEP) of GG to transcranial magnetic stimulation applied at dominant-sided anterolateral area and GG response to magnetic stimulation at the third cervical level. Stimuli were delivered at the end of expiration and inspiration respectively. The central motor conduction time (CMCT) was calculated by the latency difference between cortical and cervical stimulations.

The MEP latency and CMCT of GG in OSAS patients were shorter than those in normal subjects at the end of expiration (MEP latency: 6.08 ± 2.06 ms and 8.24 ± 2.66 ms, respectively, P < 0.05; CMCT: 2.41 ± 1.20 ms and 3.58 ± 1.53 ms, respectively, P < 0.05). However, only in normal subjects, GG MEP latency and CMCT showed significant decrease from the end of expiration to the end of inspiration. GG CMCT of OSAS patients at the end of expiration was closely correlated with AHI (r = -0.797, P = 0.002), the nadir oxygen saturation (r = 0.76, P = 0.003) and the longest apnoea time (r = -0.68, P = 0.02).

OSAS patients have an increased central motor conductivity of GG than normal subjects. Furthermore, this increased central motor conductivity of GG is related to the severity of OSAS.