Transcutaneous Electrical Stimulation on the Submental Area: The Relations of Biopsychological Factors with Maximum Amplitude Tolerance and Perceived Discomfort Level

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.

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.

Effects of Neuromuscular Electrical Stimulation (NMES) on salivary flow in healthy adults

Background

Neuromuscular electrical stimulation (NMES) is a method used for enhancing suprahyoid muscle activity and is widely applied as a treatment for dysphagia. Patients often complain of saliva pooling in the pharynx during NMES. Therefore, the purpose of this study was to investigate the changes in salivary flow during NMES.

Material and Methods

Twenty healthy adults participated in this study. Electrical stimulation was applied at constant strength for 60 minutes to the suprahyoid muscles using VitalStim®. Participants were examined under three conditions of NMES: sensory threshold plus 75% of the difference between sensory and pain thresholds (75% Stim), SensoryStim, and Sham. Saliva collections, using a 10-min spitting method, were performed seven times: before stimulation (S1), during stimulation (S2-S6), and 5 min after stimulation ended (S7).

Results

Significant differences were observed in saliva flow between S1 and S7, as well as S2 and S7 in 75% Stim.

Conclusions

This study indicates that an increase in saliva flow was promoted after NMES. Therefore, NMES may have effects on patients with xerostomia.

Key words:Neuromuscular electrical stimulation, suprahyoid muscle, sensory threshold, pain threshold, saliva flow.