Although neuromuscular electrical stimulation (NMES) is increasingly used in dysphagia therapy, patient responses to NMES are inconsistent and conflicting results have been reported. This, together with a lack of information about the effects of NEMS on the swallowing process, has led to an ongoing debate about its impact on swallowing function. In order to address this, we set out to (i) collect baseline information on the physiological effects of NMES on the complex pharyngeal phase of swallowing and (ii) to compare two different stimulation protocols. In doing so, we provide information useful for evaluating the therapeutic effectiveness of NMES on the swallowing process. In a prospective study, 29 healthy participants performed water swallows after receiving continuous NMES for 10 min. The stimulus was applied in the submandibular region using one of two different stimulation protocols: low-frequency stimulation (LFS) and mid-frequency stimulation (MFS). Swallowing parameters of the pharynx and UES were measured using high-resolution manometry. Maximum tongue base pressure increased by 8.4% following stimulation with the MFS protocol. Changes in UES function were not found. LFS stimulation did not result in any significant changes in the parameters examined. The MFS protocol enhances tongue base retraction during swallowing in healthy volunteers. The magnitude of the effect, however, was small, possibly due to the ability of healthy subjects to compensate for external influences, such as NMES, and may actually prove to be much greater in patients with diminished tongue base retraction. Thus, further studies are needed to determine whether a similar effect is also achievable in dysphagic patients with impaired bolus propulsion, possibly allowing MFS stimulation of the tongue base region to be used as an additional treatment tool.
High-resolution manometry Neuromuscular electrical stimulation Pharyngeal function Upper esophageal sphincter function Deglutition Dysphagia
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The authors are extremely grateful to Professor K. Hodges for his valuable ideas, constructive comments, and correction of the English text and to Mr. B. Vaske for his support with the statistical analyses.
M.J. supervision of acquisition of data, analysis and interpretation of data, drafting of the manuscript. C.S. acquisition, analysis, and interpretation of data, contributions to the manuscript. S.M. technical support for neuromuscular electrical stimulation, contributions to the manuscript. M.P. study concept and design, study supervision, revision of the manuscript.
Compliance with Ethical Standards
Conflict of interest
Martin Ptok and Simone Miller received refund of travel expenses from Physiomed not related to this study. All authors declare that they have no conflict of interest.
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