Effects of Submental Surface Electrical Stimulation on Swallowing Kinematics in Healthy Adults: An Error-Based Learning Paradigm

Impact of Varying Transcutaneous Electrical Stimulation Pulse Frequency on Swallow Timing Measures in Healthy Adults

The impaired swallow timing subsequent to dysphagia or aging can potentially endanger swallowing safety and efficiency. Preliminary evidence has suggested that transcutaneous electrical stimulation (TES) may have the potential to affect swallow timing. However, limited knowledge exists regarding which TES parameters can optimize swallow timing. Pulse frequency is one of the primary TES parameters that can affect the quality of muscle contraction. Yet, no clear information exists regarding how changing pulse frequency impacts the timing of swallowing events. This study aimed to investigate the varying effects of submental TES pulse frequency on swallowing events during and post-15-min TES administration. Twenty-six healthy individuals between the ages of 20 and 54 participated in this study and were assigned to high pulse frequency (HPF) (80 Hz) or low pulse frequency (LPF) (30 Hz) groups. Videofluoroscopic swallowing study (VFSS) was used to record swallowing. Three trials of 10 mL pureed mixed with barium sulfate were presented under three different conditions, including pre-TES, during TES, and post-TES, in which measures were taken following 15 min of TES delivery. The swallow timing events that were measured in each condition were time to maximum hyoid elevation, time to maximum laryngeal elevation, laryngeal vestibule closure reaction time (LVCrt), laryngeal vestibule closure duration (LVCd), time to maximum pharyngeal constriction, and pharyngoesophageal segment (PES) opening duration. No significant pulse frequency effect was found on any swallow timing measures during or after 15 min of TES. Both protocols decreased the duration of some swallowing events during TES including time to maximum hyoid elevation [p < 0.017, ηp2 = 0.185], LVCrt [p < 0.032, ηp2 = 0.158], and time to maximum pharyngeal constriction [p < 0.034, ηp2 = 0.155]. None of the significant TES effects were continued when TES ceased after 15 min. Overall, both protocols have comparable immediate effects on shortening the duration of some swallowing events during TES. Future clinical trials should examine whether these physiologic timing changes can lead to safer and more efficient swallows in patients with dysphagia.

The Impact of Vocal Task on Voice Acoustics, Effort and Discomfort Following Submandibular Neuromuscular Electrical Stimulation in Healthy Adults

BACKGROUND

Neuromuscular electrical stimulation (NMES) offers a potential adjuvant to traditional voice therapy for individuals with dysphonia. The type of vocal task to implement in conjunction with electrical stimulation to achieve maximal therapeutic benefit is unknown. The purpose of this study was to elucidate the impact of tasks on voice outcomes.

METHODS

Nineteen vocally-healthy adult females, between 23 and 27 years of age (Ave: 23.8, SD: 1.13), participated in the study. 15 participants completed all three 30-minute sessions, and four completed at least one session. NMES was paired with three different voice conditions: high-pitched hum, low-pitched hum, and comfortable-pitched hum. Acoustic (average fundamental frequency and loudness; perturbation (jitter, shimmer, noise to harmonic ratio); Cepstral Spectral Index of Dysphonia; pitch range), perceived phonatory effort, and discomfort (delayed onset muscle soreness) measures were compared across conditions.

RESULTS

Eight participants experienced discomfort following NMES. Three participants withdrew from the study due to discomfort, and one withdrew due to an unrelated oral surgery. NMES paired with high-pitch humming resulted in increased average fundamental frequency during sustained phonation and reading tasks, and increased Cepstral Spectral Index of Dysphonia during sustained phonation. Low-pitch humming resulted in a decreased noise to harmonic ratio. No statistically significant changes in perceived phonatory effort were noted.

CONCLUSION

Almost half of the participants reported temporary discomfort. Task-specific differences in some outcomes were noted indicating that the nature of voice task performed with NMES must be considered when examining the impact of NMES on voice. Vocal tasks can impact discomfort and acoustic vocal outcomes of NMES.

Healthy Volunteers Immediately Adapt to Submental Stimulation During Swallowing

OBJECTIVES

Transcutaneous stimulation above and below the hyoid is used to assist patients with swallowing disorders (dysphagia) but has shown different effects. Previously, infrahyoid transcutaneous stimulation lowered the hyoid and larynx resisting swallowing movement while suprahyoid stimulation had no effects on hyolaryngeal movement either at rest or during swallowing. More recently, large submental electrodes, covering the submental region, are used for swallowing therapy in combination with resistance therapy. To gain insight into the effects of these electrodes on movement during swallowing, we studied healthy volunteers using videofluoroscopy (VF). We hypothesized that submental electrical stimulation might elevate the hyoid but not the larynx increasing vestibular opening potentially reducing swallowing safety.

MATERIALS AND METHODS

While undergoing VF, seven healthy volunteers (mean age 51, 5 males) swallowed 5 mL of liquid barium on at least ten trials randomly ordered across three conditions: stimulation at rest, swallowing without stimulation, and swallowing with stimulation.

RESULTS

During stimulation at rest, significant (one tailed p < 0.05) anterior movement occurred in the hyoid and larynx, no superior hyoid and laryngeal movement and an increase in the distance between the hyoid and larynx. When comparing swallowing with and without submental stimulation, during stimulation volunteers significantly reduced anterior hyoid motion (p = 0.028) and increased hyoid elevation (p = 0.043) without changing anterior or superior laryngeal movement or the distance between the hyoid and larynx.

CONCLUSIONS

The healthy volunteers immediately corrected for the effects of submental stimulation by reducing hyoid anterior motion and increasing superior hyoid motion without changing laryngeal motion to prevent increased vestibule opening with stimulation. This suggests that healthy volunteers had an internal schema for swallowing movement patterning with feedforward correction for the effects of stimulation.

Submental transcutaneous electrical stimulation can impact the timing of laryngeal vestibule closure

Background

Laryngeal vestibule closure (LVC) is one of the critical airway protection mechanisms during swallowing. LVC timing impairments during swallowing are among the common causes of airway invasion in patients with dysphagia.

Objectives

To understand whether using submental transcutaneous electrical stimulation (TES) with varying pulse durations can impact the LVC reaction time (LVCrt) and LVC duration (LVCd) measures in healthy adults.

Methods

Twenty‐six healthy adults underwent three TES conditions while receiving three trials of 10 ml pureed: no TES, TES with short pulse duration (300 μs) and TES with long pulse durations(700 μs). Two pairs of electrodes were placed diagonally on the submental area. For each active TES condition, the stimulation was increased up to the participant's self‐identified maximum tolerance. Each swallow trial was recorded using videofluoroscopic swallowing study. All data were extracted and analysed offline using VideoPad Video Editor program.

Results

Submental TES reduced LVCrt during swallowing [F (2, 46) = 7.234, p < .007, ηp2 = .239] but had no significant impact on LVCd [F (2, 50) = .1.118, p < .335, ηp2 = .043]. Furthermore, pulse duration had no distinguished impact on any LVC timing measures.

Conclusion

Transcutaneous electrical stimulation may benefit patients with dysphagia who suffer from delayed LVC during swallowing. Future studies should seek whether the same physiologic effect can be observed in patients with dysphagia.

Transcutaneous Electrical Stimulation as a Resistance Force in Lingual Exercise: A Preliminary Proof-of-Concept Study

BACKGROUND

Limited knowledge exists regarding whether transcutaneous electrical stimulation (TES) based exercise can improve the lingual pressure generation.

OBJECTIVES

To compare the effect of submental TES with two different pulse durations (PD) coupled with isometric lingual exercises on lingual pressure measures.

METHODS

Twenty-eight healthy volunteers were divided into two submental TES groups: short PD (300 μs) and long PD (700 μs). The Iowa Oral Performance Instrument (IOPI) was used for lingual pressure measurements and exercise. In total, participants attended six exercise sessions three days per week for two consecutive weeks. Maximum and swallowing lingual pressures were measured one hour following each exercise session and three days after the final session to assess any detraining effect. Data were analyzed using repeated measure ANOVA.

RESULTS

Mean maximum lingual pressure change was significantly greater in TES with short PD versus the long PD condition following the first week of exercise. Following the two-week exercise, a significant increase was found in mean maximum lingual pressure for short and long PD conditions compared with the baseline. However, no significant difference was found between PD conditions for maximum lingual pressure. Likewise, no significant differences in swallowing lingual pressure were found compared with the baseline or across the two TES conditions.

CONCLUSION

Although short PD induced greater gain in maximum lingual pressure than the long PD after week 1, the enhanced effect faded after week 2, leading to a comparable increase in maximum lingual pressure for both groups. However, increased gain in maximum lingual pressure was not transferred to lingual pressure during swallowing.

Electrical, taste, and temperature stimulation in patients with chronic dysphagia after stroke: a randomized controlled pilot trial

The objective of present study was compare a traditional swallowing therapy program with a new combined swallowing therapy program including neuromuscular electrical stimulation in patients with oropharyngeal dysphagia after stroke. This pilot study included eight patients with chronic oropharyngeal dysphagia after stroke. These patients underwent traditional therapy with gustative-thermic-tactile stimulation (group A), or a new combined program adding neuromuscular electrical stimulation (group B). Study participants were evaluated before and after the intervention using fiberoptic endoscopic evaluation of swallowing with temporal measures of posterior oral spillage and whiteout time, functional oral intake scale and a visual analog scale classifies an individual's swallowing ability. The two groups did not differ in terms of posterior oral spillage time, whiteout time and functional oral intake scale. Subjects in group B exhibited significant increases in visual analog scale scores. However, both groups demonstrated improvement with decreases in posterior oral spillage time, increased whiteout time, and increased functional oral intake scale and visual analog scale scores. There was no difference in the parameters studied in both therapeutic programs in individuals with chronic oropharyngeal dysphagia after stroke.

Effects of Varying Transcutaneous Electrical Stimulation Pulse Duration on Swallowing Kinematics in Healthy Adults

Prior research in swallowing physiology has suggested that using submental transcutaneous electrical stimulation (TES) with short pulse duration (PD) (300 μs) may enhance the impact on deep extrinsic tongue muscles, thereby pulling the tongue down during swallowing. However, it was unclear whether that same TES protocol could have a differential impact on hyolaryngeal kinematics and timing. This study aimed to compare the effect of submental TES with varying PDs on anterior and superior hyolaryngeal kinematics and timing both at rest and during swallowing in healthy adults. Twenty-four healthy adults between the ages of 22 and 77 participated in this study. Anterior and superior hyolaryngeal excursion magnitude and duration measures were collected using videofluoroscopic swallowing study. Each subject swallowed three 10 ml pudding trials under three conditions: no TES, TES with short PD (300 μs), and TES with long PD (700 μs). TES was delivered using two-channel surface electrodes in the submental area. In both short and long PD conditions, TES amplitude was gradually increased until participants reached their maximum tolerance level. Videofluoroscopic data were analyzed using VideoPad Video Editor and Image J programs. One-way repeated measure ANOVAs were conducted to identify within-subject effect of TES condition. For hyoid movement, TES with short PD selectively placed the hyoid bone on a more anterior position at rest and reduced anterior hyoid excursion during swallowing compared with the no TES condition. Regarding laryngeal movement, both TES protocols resulted in the larynx taking on a more anterior position at rest and reduced anterior laryngeal excursions during swallowing when compared with the no TES condition. Varying PDs had no significant effect on the superior hyoid and laryngeal movements at rest and during swallowing. Both TES protocols induced shorter hyoid elevation duration during swallowing Findings suggest that though both TES protocols demonstrated a comparable impact on reducing anterior laryngeal excursions, the TES protocol with short PD had an enhanced effect on reducing anterior hyoid excursion during swallowing. This reduced range of motion may result from stimulating the deep submental muscles, which primarily place the hyoid and larynx into a more forward position before swallowing onset. Overall, the TES protocol with short PD may have an increased benefit in facilitating swallowing in patients with dysphagia.