Differential effects of neuromuscular electrical stimulation parameters on submental motor-evoked potentials.
BACKGROUND
Neuromuscular electrical stimulation (NMES) of the muscles underlying the pharynx and faucial pillars affects the excitability of corticobulbar projections in a frequency- and duration-specific manner. The anterior hyomandibular (submental) muscles are primary targets for the clinical application of NMES to improve disordered swallowing, but the optimal NMES parameters for this application are unknown.


OBJECTIVE
To determine the influence of NMES parameters on the excitability of corticobulbar projections to the submental musculature.


METHODS
Transcranial magnetic stimulation (TMS) was used in event-related protocols, triggered by either volitional contraction of the submental muscles or pharyngeal swallowing, to assess corticobulbar excitability prior to, immediately following, and 30, 60, and 90 minutes post-NMES in 25 healthy volunteers. In the first 2 experiments, 4 stimulus frequencies (5, 20, 40, and 80 Hz) and 3 NMES dosages, manipulated through stimulus train durations or number of repetitions, were evaluated. The optimal excitatory NMES triggered by volitional swallowing (event-related NMES) was then replicated in a new sample and contrasted with non-event-related NMES (either discrete events or continuously for 1 hour).


RESULTS
It was found that 80Hz NMES increased motor-evoked potential (MEP) amplitude at 30 minutes and 60 minutes poststimulation only after 60 repetitions of 4-s event-related NMES trains. Non-event-related and continuous NMES did not affect MEP amplitudes. No changes in MEP onset latencies were observed.


CONCLUSIONS
Changes in corticobulbar excitability induced by NMES of the submental muscle group are frequency and dose dependent and only occur after NMES triggered by volitional swallowing. Underlying neural mechanisms are discussed.
University of Canterbury, Christchurch, New Zealand. sebastian.doeltgen@adelaide.edu.au
Sebastian H
SH
Doeltgen
John
J
Dalrymple-Alford
Michael C
MC
Ridding
Maggie-Lee
ML
Huckabee
D000328:Adult; D003679:Deglutition / Q000502:physiology; D003680:Deglutition Disorders / Q000503:physiopathology / Q000628:therapy*; D004599:Electric Stimulation Therapy / Q000295:instrumentation / Q000379:methods*; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009334:Neck Muscles / Q000294:innervation / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology*; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D016896:Treatment Outcome