Dysphagia occurs in 45% to 65% of patients after acute stroke,1 , 2 and it is the most significant risk factor for the development of pneumonia. Pneumonia accounts for approximately 34% of all stroke-related deaths and is the third-highest cause of death during the first month after stroke, although not all these pneumonias are caused by aspiration of food following attempted eating.3 Untreated dysphagia delays the functional recovery and substantially affects the quality of life.4 Therefore, detecting and managing dysphagia as early as possible is critical for patients after stroke. Oropharyngeal motor dysfunction is an important cause of swallowing disorder after stroke.1 In addition, it has been suggested that pharyngeal sensory impairment is common after acute stroke and that such impairment is associated with an increased risk of aspiration and aspiration pneumonia.5
Electrical stimulation has been reported as a treatment for pharyngeal dysphagia in recent studies.6 Neuromuscular electrical stimulation (NMES) uses surface electrodes to contract local muscles by delivering electrical stimulation to depolarize of nerve fibers. Logemann7 reported that the therapeutic effect of VitalStim therapy lacks convincing supporting evidence. Therefore, the therapeutic effect of VitalStim therapy needs further clinical investigation; its efficacy is uncertain.8 , 9 NMES has been extensively used to treat dysphagia in China. Our study hypothesis was that patients who underwent a treatment with NMES for dysphagia would have a better outcome compared with those who did not receive this therapy.
So, the aim of our study was to assess whether adding NMES (VitalStim) to conventional therapy can improve dysphagia in patients with stroke in China.
This was a 4-week, prospective, single-blinded, randomized controlled trial with 2 measurement points (before treatment and after 4 weeks of treatment). The assessors were blinded to participants' treatment assignments. Preliminary power analysis indicated that an equal sample size of 45 would be sufficient for each group. This study was approved by the Wuxi-Affiliated Hospital of Nanjing University of Chinese Medicine Institutional Review Board.
Swallowing difficulties after patient with stroke were recruited through newspaper advertisement and flyers. All participants provided informed consent before participating in the study. All patients had to meet with the diagnosis criteria of dysphagia after stroke.10 Inclusion criteria for the trial were as follows:
- Patients had to be 50 to 80 years old and had cerebrovascular disease (stroke) more than 3 months prior to the study.
- Patients with hemispheric stroke and without neurologic signs typical for brainstem involvement.
- Patients could not have nasogastric tubes but could have percutaneous endoscopy gastrostomy.
- Patients had to be able to elicit some pharyngeal swallow as revealed during videoradiographic swallowing evaluation and seen as anterior movement of the hyoid bone and constrictor activity in the pharyngeal wall.
- They had to be able to communicate. The disease process should have been stable. The stroke could have been a first-time stroke or a recurrence. Patients could be on a modified diet and may practice swallowing maneuvers.
Exclusion criteria for the trial were as follows:
- Patients with progressive cerebrovascular disease;
- Patients with other neurologic diseases such as amyotrophic lateral sclerosis, multiple sclerosis, or Parkinson disease;
- Patients with tumors or neoplastic diseases of the swallowing apparatus and who had undergone radiotherapy to the neck;
- Patients who had undergone surgery to the swallowing apparatus;
- Patients who were not able to elicit pharyngeal swallow (as described earlier);
- Patients with a nasogastric tube.
The number of participants in the treatment arms at each stage of the study is shown in the CONSORT diagram in Figure 1. All participants were asked to maintain their regular diet, medication if any, and normal daily activities and lifestyle throughout the study.
The patients recruited were randomly divided into a VitalStim therapy group, or a traditional swallowing therapy group (TT), or a VitalStim plus TT group (VitalStim + TT) after stratification using minimizing software.11 There were no statistically significant differences in age, gender, cause of dysphagia, duration, and severity of the condition among the 3 groups. After signing the informed consent form, each subject received a sealed envelope indicating her group assignment.
Electrical stimulation was applied by an occupational therapist, using a modified handheld battery-powered electrical stimulator (VitalStim Dual Channel Unit and electrodes, Chattanooga Group, Hixson, Tennessee). The skin of the anterior neck was cleaned with 70% isopropyl alcohol cotton. Two sets of electrodes were used. The top set was placed in the submental region between the anterior belly of the digastric muscle and hyoid bone, and the hyoid bone and thyroid cartilage. The bottom set was placed on the skin between the thyroid cartilage and cricoid cartilage and below the cricoid cartilage (Figure 2). We stimulated the muscles responsible for swallowing, such as the digastric muscle, mylohyoid muscle, and thyrohyoid muscle. NMES carries possible risks, including laryngospasm, arrhythmia, hypotension, glottic closure, and burns. We explained the possible adverse effects to the patients before treatment, and we closely observed and recorded every treatment session. After familiarizing the participant with the device, we identified the sensory threshold as the lowest current level at which the participant reported a “tingling” sensation on the skin. The amplitude of the electrical current level was approximately 7 mA. The therapy sessions were for 1 hour at a frequency of 5 per week. The VitalStim device cycles automatically from “on” to “off” to “on” again for 1 second every minute. Because the change in stimulation is ramped, this cycling process takes up to 4 seconds, the therapy sessions they were not swallowing.
The traditional swallowing therapy included basic training and direct food intake training. The basic training (ie, functional recovery training) referred to indirect training of organs related to food intake and swallowing. Direct food intake training involved several aspects including food intake environment, body posture for swallowing, and removal of pharyngeal food residue. Direct food intake training was used primarily for mild dysphagia.
The visual analog scale (VAS) was used to compare differences between pre- and posttreatment with muscle pain. The number of points before and after treatment was also compared: 0 point = no difficulties at all; and 10 points = maximum/unable to swallow. A comparison was made between the patient's subjective feeling (ie, the VAS) and the objective pharyngeal function (videoradiography). The standardized swallowing assessment (SSA) was used for the evaluation of swallowing function.12 , 13 Surface electromyography (sEMG) signals of swallowing muscles were collected through the use of Flexcomp Biomonitoring System (Thought Technology, Canada) and analyzed by using Flexcomp Infiniti software that goes with the system. After patient swallowed 2 mL of water, the maximum amplitude of sEMG signals was measured, and the average of 3 measurements was calculated.14–17 Videofluoroscopy swallowing function was evaluated using a standardized videofluoroscopic barium swallow.
Lateral and anteroposterior projection fluoroscopic images were acquired using a radio amplifier (Flexiview 8800, General Electric, United Medical Technologies Corp, Fort Myers, Florida) and recorded on a computer at 12 frames per second for later analysis (MMS, Tubingen, the Netherlands). The patients first swallowed three 5-mL boluses of high-density puree-consistency barium suspension and then three 5-mL boluses of high-density liquid-consistency barium suspension. Bolus transit measurements included oral transit time (OTT), pharyngeal transit time (PTT), and laryngeal closure duration (LCD). Aspiration was scored using a validated 8-point penetration-aspiration scale.18 The investigators were blinded to whether the videofluoroscopy studies were pre- or postintervention.
Statistical analysis was conducted using SPSS 12.0 software. Descriptive data were reported as mean (standard deviation, SD) for baseline characteristics. If data not normally distributed, we used a Kruskal-Wallis test. Paired t tests were conducted to compare continuous variables between 3 groups before treatment. Each outcome measure of balance, sEMG values, SSA and VFSS scores was presented as mean (SD). For the analyses of sEMG values and VAS, SSA, and VFSS scores, an independent-samples t-test or a paired t test was employed to show the main effect between 3 groups. Correlation analysis was performed using the Pearson test. A level of P < .05 was considered to be statistically significant.
Table 1 summarizes the demographic characteristics and medical status of the subjects. Baseline comparability tests confirmed no significant differences between 3 groups in all demographic variables and medical status. No other adverse effect associated with the practice of NMES (VitalStim) was reported by the participants.
A total of 135 subjects were recruited and initially enrolled in the study and randomly assigned to 4 weeks of 3 groups. Details of attrition are shown in Figure 1. Analysis showed no significant difference in the demographic and baseline measures between the dropouts and participating subjects (P > .05). Seventeen subjects dropped out (7 in the VitalStim + TT group, 5 in the VitalStim group, and 5 in the TT group) (12% attrition), due to time conflict, travel, illnesses unrelated to the intervention, and family/private reasons, before completing the study. In addition, subjects were asked to report at each measurement session any change in any medication or additional exercise regimen during the intervention period. No changes were reported by the subjects.
Table 2 presents the median and the 25th and 75th percentiles of the patient's self-evaluation of dysphagia. Statistically significant therapy effects were found for the total group of patients. No statistically significant differences were found between the VitalStim group and the TT group (independent-samples t test). The outcome from the VAS showed that baseline data of the VitalStim group were more severe than those of the TT group.
Prior to treatment, there were no significant differences in SSA scores among 3 groups (P > .05). After treatment, SSA scores in each group were significantly increased compared with those prior to treatment. After treatment, SSA scores were significantly increased in the VitalStim therapy plus traditional swallowing therapy group than in the traditional swallowing therapy group and the VitalStim therapy group (P < .01), but there were no significant differences in these scores between the traditional swallowing therapy group and the VitalStim therapy group (P > .05) (Table 3).
Following the electrical stimulations, swallowing coordination improved, with a decrease in swallow OTT, PTT for the liquid (P < .05) and paste (P < .05) boluses in the VitalStim therapy plus traditional swallowing therapy group, and then in the traditional swallowing therapy group and the VitalStim therapy group (P < .05), but there were no significant differences in these scores between the traditional swallowing therapy group and the VitalStim therapy group (P > .05) (Table 4); LCD did not change significantly.
After treatment, the maximum amplitude of sEMG signal in each group was significantly increased (P < .01). After treatment, the maximum amplitude of sEMG signal in the VitalStim therapy plus traditional swallowing therapy group was significantly increased in comparison with the traditional swallowing therapy group and the VitalStim therapy group (P < .01), but no significant difference was found between the traditional swallowing therapy group and the VitalStim therapy group (P > .05) (Table 3).
Correlation analysis was performed for the SSA scores and sEMG, VAS, and VFSS (OTT, PTT, and LCD) values in each group before and after treatment. It showed a strong correlation among tests (P < .01) (Table 5).
The act of swallowing is a very complicated, multilevel, neuromuscularly integrated event. The inability to swallow has great implications for personal nutrition, health, and social interactions. In recent years, a large number of studies on poststroke dysphagia have been conducted to investigate its treatment and management strategies, and a wide array of novel therapeutic approaches are being developed.19–21
NMES uses designated electric impulses to stimulate pharyngeal muscles and elicit muscle contraction or mimic normal automatic contraction, thereby improving or recovering the function of stimulated muscles. VitalStim therapy is a specific NMES that requires patients with poststroke dysphagia to perform a series of procedures including perception of swallowing action, followed by initial automatic swallowing, and then completely automatic swallowing.7
Results from this study demonstrated the following:
- VitalStim therapy and conventional swallowing training do not yield obviously different effects on sEMG values and SSA and VFSS scores in patients with poststroke dysphagia, indicating that these 2 techniques produce similar therapeutic effects on poststroke dysphagia, which is consistent with a previous report.14
- The swallowing function was obviously improved in patients receiving VitalStim therapy or conventional swallowing therapy, indicating that VitalStim therapy and conventional swallowing therapy are both effective for poststroke dysphagia. This is consistent with previous reports. For example, Gallas et al14 reported that NMES can improve the swallowing function by enhancing swallowing coordination of patients with poststroke dysphagia. Ludlow et al22 concluded that surface electrical stimulation can help raise the hyoid bone of patients during swallowing. Park et al23 observed that electrical stimulation can increase the range of motion of hyoid bone if swallowing action can be actively cooperated. Freed et al24 thought that electrical stimulation yields better therapeutic effects than hot-cold stimulation.
Leelamanit et al25 reported that electrical stimulation can increase pharyngeal and laryngeal activities by increasing the contraction force of hyoid bone muscle.
In clinical practice, a combination of several techniques, rather than 1 method, is often used to enhance the therapeutic effects on poststroke dysphagia. The present study was designed to compare the curative effects of the VitalStim therapy coupled with conventional swallowing therapy and the conventional swallowing therapy or VitalStim therapy alone. This study demonstrated that the sEMG value and SSA and VFSS scores in the VitalStim therapy plus conventional swallowing training group were significantly higher than those in the conventional swallowing training group and the VitalStim group (P < .01), indicating that the VitalStim therapy coupled with conventional swallowing therapy is the best alternative for improving poststroke dysphagia. The possible mechanisms10 , 26 are as follows:
- Repeated rehabilitation training and electrical stimulation help reconstruct cerebral functions or arouse resting synapses to transmit nerve impulses.
- Elicit muscular contraction and prevent disuse atrophy.
- Accelerate the recovery of swallowing muscle power.
Results of the correlation analysis on SSA scores and sEMG, VAS, and VFSS (OTT, PTT, and LCD) values before and after treatment exhibited that there was a good correlation between any 2 indices, suggesting any of the test can serve as a surrogate to the gold standard in evaluating the swallowing function. Transcutaneous NMES for patients with dysphagia utilizes an established therapy for a novel application. Patients generally are very positive regarding its results. We believe that NMES (VitalStim therapy) is an important addition to the armamentarium of the swallowing therapist. However, in the patients with the most severe dysphagia, who rely solely on enteral feedings, optimism must be tempered. More large objective clinical studies are necessary to determine which patients will most likely succeed with this technique.
One limitation of this study was the absence of a sham stimulation group. This was due to the limited time and the complications of recruiting an adequate sample. Future studies, using similar stimulation protocols with a larger sample, are needed to gain further insight into the potential to induce functionally beneficial neuroplasticity in patients with stroke.
VitalStim therapy coupled with conventional swallowing therapy can alleviate poststroke dysphagia and thereby improve patients' quality of life. Studies involving larger subject population are needed, and long-term curative effects of this combined method warrant further investigation.
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