1. Introduction

The surface or neuromuscular electrical stimulation (NMES), due to its capacity to increase muscular performance, is a technique to be taken into account to improve the efficacy of the physiotherapeutic treatment in DP patients. However, its appropriate application parameters have not yet been described, such as intensity (sensitive threshold, motor or a specific range), frequency, impulse time and electrode placement. Therefore, it was considered necessary to carry out a literature review of the scientific research published in the last years, with the aim of evaluating the efficacy of the various parameters of application of the NMES in DP generated after a stroke.

2. Methods

The PICO question was then chosen as follows: P-population: DP patients after stroke; I-intervention: NMES; C-control: conventional physiotherapy techniques; O-outcome: swallowing efficacy (level of oral intake presence and severity of penetration and aspiration, oral and pharyngeal transit times…); S-study designs: experimental studies. The systematic search of publications was conducted in March 2020 in the Pubmed, Cinahl, Medline, Web of Science and Scopus databases, using the following words as search terms of the Medical Subject Headings (MeSH) thesaurus: Electrical stimulation therapy, Deglutition disorders and Stroke; and Dysphagia as a free term.

3. Results

A total of 21 articles were found, of which eleven were focused on experimental researchs [1-11] and nine were randomized-controlled trials [12-21].

The studies that applied NMES as a single treatment technique [2-4, 9] reported the beneficial effect of this method on DP, as had already been corroborated in a previous meta-analysis [22]. However, the benefits are multiplied when its application is combined with other interventions, such as manual therapy [8, 10, 11, 14-16, 18, 19, 21] and conventional swallowing therapy [1, 5, 6, 8, 11, 12, 14-16, 18-21]. The greater efficacy of the treatments that combine conventional techniques with NMES had already been observed with longer-lasting effects and shorter intervention times [23, 24].

Regarding the different variables analysed, one of the most repeated ones was the analysis of the level of oral intake [7, 14, 15, 17, 19, 20]. This variable improved significantly with all the interventions [14, 15, 17, 20], except for the studies of Mituuti et al. [7], who did not define the impulse time (a parameter that, if chosen incorrectly, can lead to the loss of intervention efficacy), and Guillèn-Sóla et al. [19], who used the sensitivity threshold as the impulse intensity, thus they may have not achieved an effective stimulation of the muscle fibres. It is important to highlight that Sproson et al. [17], in their evaluation of this variable three months after the intervention, observed that the initial improvements achieved were conserved. 

The presence and severity of penetration and aspiration was also evaluated [2, 7, 9, 11, 15, 17, 19], obtaining significant improvements in all cases, except in the study that applied NMES at low intensity [7], in which the sessions were excessively long [19], and in the study in which the authors did not use individualised paremeter regarding intensity [11].

The oral and pharyngeal transit times are very important parameters for the valuation of patients with DP, since these indicate the time that the alimentary bolus takes to reach the upper esophageal sphincter from the oral cavity. These improved with all the analysed interventions [2-5, 7, 9, 12, 21], except, once again, in the study in which NMES was applied up to the sensitivity threshold [7].

NMES has positive effects on the treatment of DP associated with a stroke: it improves the quality of life of the patient, reduces aspirations, restores the capacity to intake solids and reduces the socioeconomic impact of this condition. This technique has beneficial effects as a single treatment, although the attainment of therapeutic objectives is faster when it is combined with active work from the patient, simultaneously, and also when applied as part of a programme that includes other swallowing techniques or exercises. 

The application parameters of NMES should be: a frequency of 60-80 Hz, 700 µs of impulse time, an intensity above the motor threshold (respecting the patient’s tolerance) and an application time of 20-30 minutes, placing the electrodes in the anterior side of the neck. Simultaneously, the patient must be requested to make voluntary contractions of the deficient muscles in order to optimise the increase of muscular strength. Finally, if this technique is part of a treatment that also includes conventional swallowing treatment techniques or strengthening exercises, the treatment objectives can be attained sooner (with treatment durations of four weeks).

It is recommended to carry out further studies with reliable methodology to establish the most adequate application parameters for NMES and determine the most appropriate combination of techniques to be performed simultaneously and in the same session. This will allow protocolising the use of NMES for the treatment of DP with the aim of reaching the best effects in the shortest time possible.

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