Surface Electrical Stimulation for Treating Swallowing Disorders after Stroke: A Review of the Stimulation Intensity Levels and the Electrode Placements

Table 1

A summary of reviewed studies.

Authors	Study design	Number of subjects in groups	Site of lesion	Number of sessions in groups	Reported stimulation parameters	Reported electrode location	Outcomes
Freed et al. (2001) [10]	Controlled study	Group 1 (ES^a): 𝑛=63; stroke patients; Group 2 (TTS^b): 𝑛=36; stroke patients	*Group 1; Brainstem = 7; Hemispheric = 29; Multiple strokes = 24; *Group 2; Brainstem = 1; Hemispheric = 19; Multiple strokes = 8	Group 1: 5.5 sessions (mean); Group 2: 6.0 sessions (mean) (𝑃=0.36)	Frequency: 80 Hz; Pulse width: 300 𝜇s; Intensity: 2.5 to 25 mA; Duration: 60 minutes a day for 5 days a week; Motor level	Digastric and thyrohyoid muscles	Group 1. Initial swallow score in SFSS^c = 0.76 ± 1.04; Posttreatment swallow score in SFSS = 4.52 ± 1.69; (𝑃=0.0048); Group 2. Initial swallow score in SFSS = 0.75 ± 1.20; Posttreatment swallow score in SFSS = 1.39 ± 1.13; (𝑃<0.0001)
Bülow et al. (2008) [26]	Randomized trial	Group 1 (ES): 𝑛=12; stroke patients (>3 months); Group 2 (TDT): 𝑛=13; stroke patients (>3 months)	Group 1: only hemispheric stroke; Group 2: only hemispheric stroke	Group 1: 15 sessions; Group 2: 15 sessions	Intensity: 4.5 to 25 mA; Duration: 60 minutes a day for 5 days a week over 3 weeks; Motor level	Thyrohyoid muscles	Group 1. Initial median score in ANS^g = 2.5; Posttreatment median score in ANS = 1.5; Group 2. Initial median score in ANS = 3; Posttreatment median score in ANS = 3
Permsirivanich et al. (2009) [27]	Randomized controlled study	Group 1 (ES + oral motor exercises): 𝑛=12 patients with postacute stroke (>2 wk); Group 2 (RST^h): 𝑛=11 patients with postacute stroke (>2 wk)	NR	Group 1: 17.25 ± 5.64 sessions (mean ± SD); Group 2: 18.36 ± 3.23 sessions (mean ± SD); (𝑃=0.57)	Frequency: 80 Hz; Pulse duration: 700 ms; Duration: 60 minutes a day for a 5 days a week; Motor level	Thyrohyoid muscles	Group 1. Average changes in FOIS^i score = 3.17 ± 1.27; Group 2. Average changes in FOIS score= 2.46 ± 1.04 (𝑃<0.001)
Park et al.; (2012) [28]	Randomized controlled study	Group 1 (effortful swallow + motor ES): 𝑛=9 patients with stroke (>1 month); Group 2 (effortful swallow + sensory ES): 𝑛=9 patients with stroke (>1 month)	NR	12 sessions	Group 1: Frequency: 80 Hz; Pulse width: 700 𝜇s; Intensity: 7.33 ± 1.12 mA; Duration: 20 min per week for 4 weeks; Motor level; Group 2: Frequency: 80 Hz; Pulse width: 700 𝜇s; Intensity: 2.89 ± 1.05 mA; Duration: 20 min per week for 4 weeks; Sensory level	Sternohyoid muscles	Group 1. A significant increase in the vertical movement of the larynx; (𝑃<0.05); A nonsignificant increase in the vertical movement of the hyoid the UES^l opening; (𝑃=0.066); No significant changes in anterior movement and the PAS; Group 2. No significant increase in all biomechanical outcome measures; No significant changes in the PAS
Lim et al.; (2009) [20]	Randomized controlled study	Group (ES + TTS): 𝑛=16; Group 2 (TTS): 𝑛=12	Group 1; Subcortical = 12; Brainstem = 2; Hemispheric = 2; Group 2; Subcortical = 8; Brainstem = 2; Hemispheric = 2	Group 1: 20 sessions; Group 2: 20 sessions	Intensity: approximately 7 mA; Duration: 60 minutes a day for 5 days a week; Sensory level	Digastric, mylohyoid, and thyrohyoid muscles	Group 1. Difference in PAS^j scores after treatment (semisolid and liquid) = 2 and 2.5; (𝑃<0.05); Difference in swallow function scores after treatment = 2; (𝑃<0.05); Difference in PTT^k after treatment (semisolid and liquid) = 0.11 and 0.10; (𝑃<0.05); Group 2. Difference in PAS scores after treatment (semisolid and liquid) = 0 and 0; (𝑃>0.05); Difference in swallow function scores after treatment = 0; (𝑃>0.05); Difference in PTT after treatment (semisolid and liquid) = 0.01 and 0.02; (𝑃>0.05)
Gallas et al.; (2010) [29]	Outcome study	One group (ES): 𝑛=11; patients with chronic poststroke dysphagia	Hemispheric = 7; Brainstem = 4	5 sessions	Frequency: 80 Hz; Mean intensity: 4.8 V (sensory threshold); Duration: 60 minutes a day for 5 consecutive days; Sensory level	Submental muscles	Initial average of dysphagia handicap index scores = 31 ± 7; Posttreatment average of dysphagia handicap index scores = 23 ± 7; (𝑃<0.05); Aspiration and residue scores decreased after ES; (𝑃<0.05); The swallow response time decreased after ES; (𝑃<0.05)