Introduction Previous reports have revealed that excitation of human pharyngeal motor cortex can be induced by pharyngeal electrical stimulation (PES)1 and swallowing carbonated water (CW).2 This study is aimed to investigate whether synchronously combining PES with swallowing (of still water, SW or CW) can potentiate this excitation in pharyngeal cortical area and brainstem. Our hypothesis was that combining inputs would potentiate cortico-pharyngeal excitability compared to each alone which would be more advantageous in the rehabilitation of dysphagic patients. For the evaluation of the excitation in pharyngeal cortex or brainstem, Transcranial or transcutaneous Magnetic Stimulation (TMS) was used to stimulate the corticobulbar and craniobulbar neural networks.
Methods Fourteen healthy volunteers (4 females, age range 19–35 yrs) participated and were intubated with an intraluminal catheter for delivering PES and recording pharyngeal electromyography. Each participants underwent the baseline corticobulbar, craniobulbar and hand motor evoked potential (MEP) measurements with TMS. Subjects were then randomised to receive one of four 10 minute interventions (PES only, ShamPES+CW, PES+CW and PES+SW). Corticobulbar, craniobulbar and hand MEPs were then re-measured for up to 60 minutes. Data were analysed using ANOVA and post hoc t-tests.
Results Two way rmANOVA comparing pharyngeal MEP amplitude changes in the dominant hemisphere for Interventions×Time showed a significant interaction, F(15, 195) =2.826, P < 0.01. One-way ANOVA for each Interventions indicated significant changes for PES only (P < 0.01) and Sham PES+CW (P < 0.05) but not for PES+CW or PES+SW over time. Subsequent post hoc t-tests with Bonferroni correction showed the main increase took place at the immediate follow-up for Sham PES+CW (**P < 0.01) and at 45 and 60 minutes for the PES only intervention (*P < 0.05) (Fig). One-way ANOVA for each interventions comparing excitability in the brainstem circutry indicated significant amplitude changes only for PES+CW (P < 0.05).
Conclusion Of the interventions applied, only PES alone was able to induce sustained changes in pharyngeal cortical excitability that built up over time. By contrast, combination stimuli were less effective in promoting enhanced cortical excitability. Of interest, combination stimuli did produce short-term increases in excitability in brain stem reflexes. Our data suggest that PES alone may be most advantageous in dysphagic patients who have a difficulty in performing voluntary swallows.
References 1 Fraser, et al. Neuron 2002; 34:831–40.
2 Elshukri, et al. J Appl Physiol 2016; 15;120:408–15.
Disclosure of Interest None Declared
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