Lasting modulation of human cortical swallowing motor pathways following thermal tongue stimulation

Effects of carbonated beverages on sustained swallowing behavior changes in older inpatients

Sensory stimulation, including stimulation with carbonated liquids, has been known to influence swallowing activity. The aim of this study is to determine the effect of sustained changes in the swallowing behavior of hospitalized patients without dysphagia using the cervical auscultatory recordings of swallowing sounds. The study participants were hospitalized older adults without dysphagia. The participants were asked to initially swallow water and then a carbonated beverage. The sustained effects of the carbonated beverage in relation to swallowing movements were evaluated by measuring the swallowing sounds at the following time periods: (1) immediately and (2) at 1 to 9 minutes with intervals of 2 minutes after swallowing the carbonated beverage. The swallowing sounds before and after swallowing the same volume of water were also measured and compared on a different day. Analysis was performed to calculate the time from a sound signal to the beginning of the swallowing sound. Significant shortening of the swallowing sound time of the late pharyngeal phase was observed up to 7 minutes after swallowing the carbonated beverage, except during the 3 minutes after swallowing. Shortening of the whole swallowing sound time was observed only immediately after swallowing the carbonated beverage. Regarding the shortening of the acoustic signal in the late pharyngeal period, the effect of cerebral excitability changes due to carbonic acid stimulation was considered.

Sensory neuromuscular electrical stimulation for dysphagia rehabilitation: A literature review

BACKGROUND

Dysphagia is a common disorder following a cerebrovascular accident. It can cause detrimental effects on patient's quality of life and nutrition intake, especially in older adults. Neuromuscular electrical stimulation has been one of the management strategies for acceleration of the recovery. This review summarises the current evidence on sensory threshold stimulation of the procedure.

METHOD

This review compiled data from the Internet database PubMed, Cochrane Library and Scopus using combination of MeSH thesaurus: 'Sensory threshold', 'electrical stimulation', 'neuromuscular stimulation', 'Deglutition', 'Dysphagia'. Eleven studies were intergraded into the review.

RESULTS

Most of the studies show significant improvement to the outcomes of sensory neuromuscular electrical stimulation treatment. In many cases, the results of the treatment are comparable or superior to motor threshold stimulation and conventional therapy. However, the study design and parameters of the procedure varied greatly without conclusive standardised guidelines.

CONCLUSION

The sensory neuromuscular electrical stimulation (SNMES) is a viable treatment option for treating oropharyngeal dysphagia. The most suggested application parameters are an intensity at sensory threshold, a frequency of 80 Hz, an impulse time of 700 μs, a combined total duration of 20 h of stimulation in a 2-week period, and placing the electrodes in the submental area of the neck. However, further research is necessary to construct a definitive guideline for clinicians.

Electrophysiological Measures of Swallowing Functions: A Systematic Review

The purpose of this systematic review was to examine the application of event-related potentials (ERPs) to investigate neural processes of swallowing functions in adults with and without dysphagia. Computerized literature searches were performed from three search engines. Studies were screened using Covidence (Cochrane tool) and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement standards (PRISMA-2009). A total of 759 studies were initially retrieved, of which 12 studies met inclusion criteria. Electrophysiological measures assessing swallowing functions were identified in two major ERP categories: (1) sensory potentials and (2) pre-motor potentials. Approximately 80% of eligible studies demonstrated strong methodological quality, although most employed a case series or case-control study design. Pharyngeal sensory-evoked potentials (PSEPs) were used to assess pharyngeal afferent cortical processing. The temporal sequence of the PSEP waveforms varied based on the sensory stimuli. PSEPs were delayed with localized scalp maps in patients with dysphagia as compared to healthy controls. The pre-motor ERPs assessed the cortical substrates involved in motor planning for swallowing, with the following major neural substrates identified: pre-motor cortex, supplementary motor area, and primary sensorimotor cortex. The pre-motor ERPs differed in amplitude for the swallow task (saliva versus liquid swallow), and the neural networks differed for cued versus non-cued task of swallowing suggesting differences in cognitive processes. This systematic review describes the application of electrophysiological measures to assess swallowing function and the promising application for furthering understanding of the neural substrates of swallowing. Standardization of protocols for use of electrophysiological measures to examine swallowing would allow for aggregation of study data to inform clinical practice for dysphagia rehabilitation.

Chewing modulates the human cortical swallowing motor pathways

When eating, mastication is always followed by swallowing. The present study assessed the effect of mastication on swallowing-related neural pathways in humans. Twenty healthy volunteers participated and underwent baseline transcranial magnetic stimulation to evaluate cortico-pharyngeal and cortico-hand motor-evoked potentials (MEPs). Next, they performed a chewing task and a swallowing task. Repeated-measures ANOVA revealed that pharyngeal MEPs were significantly higher after the swallowing task than after the chewing task, even though the number of swallows across tasks was matched. This implies that chewing movements suppress swallowing-related activity in the pharyngeal motor circuit.

Theta burst stimulation versus high-frequency repetitive transcranial magnetic stimulation for poststroke dysphagia: A randomized, double-blind, controlled trial

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) of high-frequency (10 Hz) on suprahyoid motor cortex has been an evidence-based treatment for poststroke dysphagia. Intermittent theta burst stimulation (iTBS) can be performed in 3 minutes compared with 20 ± 5 minutes for 10 Hz rTMS. This study aimed to ensure the clinical efficacy, safety, and tolerability of iTBS compared with 10 Hz rTMS for patients with poststroke dysphagia.

METHOD

In this randomized, double-blind, single-center, controlled trial, 47 participants were randomly assigned to iTBS (n = 24) and rTMS (n = 23) group. Each participant received iTBS or rTMS daily at suprahyoid motor cortex of affected hemisphere for 10 consecutive days. The outcomes were assessed at baseline, immediately, and 2 weeks after intervention, including water-swallowing test, standardized swallowing assessment, Mann assessment of swallowing ability, Murray Secretion Scale, Yale Pharyngeal Residue Severity Rating Scale, Penetration-Aspiration Scale, and motor evoked potential (MEP) of bilateral suprahyoid muscle.

RESULTS

There were no significant differences between groups. There was a significant improvement on all rating scales and MEP after rTMS and iTBS. No significant differences on water-swallowing test, Mann assessment of swallowing ability, standardized swallowing assessment, Murray Secretion Scale scores, and MEP were observed between groups. In particular, there was significant differences on Penetration-Aspiration Scale scores (viscous liquid: mean difference = 1.016; 95% CI: 0.32-1.71; effect size: 0.360; P = .005) and the residue rate of pyriform fossa (viscous liquid: mean difference = 0.732; 95% CI: 0.18-1.28; effect size: 0.248; P = .010) in between-group. Comparing the differences over the changes of all rating scales, only the residue rate of epiglottis valley between groups was found to be significantly different (dilute liquid: mean difference = -0.567; 95% CI: -0.98 to -0.15; P = .009). There was no severe adverse effect and high dropout rates in both groups.

CONCLUSION

The clinical efficacy, safety, and tolerability of iTBS showed non-inferior to 10 Hz rTMS for patients with poststroke dysphagia. The present study can be used to improve the clinicians' knowledge and clinical decision skills on iTBS and rTMS for poststroke dysphagia.

A systematic review and meta-analysis of the effects of intraoral treatments for neurogenic oropharyngeal dysphagia

BACKGROUND

Rehabilitative treatments for oropharyngeal dysphagia, including oromotor exercises and sensory stimulation, have been widely adopted into clinical practice. However, the effects of these treatments are mainly supported by exploratory studies. As such, their clinical efficacy remains uncertain.

OBJECTIVE

Our systematic review and meta-analysis aimed to evaluate the efficacy of intraoral treatments for neurogenic oropharyngeal dysphagia based on evidence from randomised controlled trials (RCTs).

METHODS

Six electronic databases were systematically searched between January 1970 and July 2021. Data were extracted and analysed by two independent reviewers. The outcome measure was changes in (any) relevant clinical swallowing-related characteristics.

RESULTS

Data from 285 dysphagic patients were collected from 8 RCT studies across a range of intraoral dysphagia treatments. The pooled effect size of all intraoral dysphagia treatments was non-significant compared to control comparators (SMD [95%CI] = 0.23 [-0.22, 0.69], p = .31; I²  = 73%). Subgroup analysis revealed that the pooled effect sizes were also non-significant for oromotor exercises (device-facilitated lip resistance exercises and tongue exercises) (SMD [95%CI] = 0.11 [-0.76, 0.97]; p = .81; I²  = 88%) and sensory stimulation (thermal-tactile, thermo-chemical and electrical stimulation) (SMD [95%CI] = 0.35 [-0.03, 0.72]; p = .07; I²  = 0%).

CONCLUSIONS

Our results showed that overall, intraoral dysphagia treatments, including oromotor exercises and sensory stimulation, do not show beneficial effects for neurogenic oropharyngeal dysphagia. The evidence for these treatments remains weak and currently inadequate to support clinical use. Large-scale, multi-centre RCTs are warranted to fully explore their clinical efficacy.

Metaplasticity in the human swallowing system: clinical implications for dysphagia rehabilitation

Dysphagia is a common and devastating complication following brain damage. Over the last 2 decades, dysphagia treatments have shifted from compensatory to rehabilitative strategies that facilitate neuroplasticity, which is the reorganization of neural networks that is essential for functional recovery. Moreover, there is growing interest in the application of cortical and peripheral neurostimulation to promote such neuroplasticity. Despite some preliminary positive findings, the variability in responsiveness toward these treatments remains substantial. The purpose of this review is to summarize findings on the effects of neurostimulation in promoting neuroplasticity for dysphagia rehabilitation and highlight the need to develop more effective treatment strategies. We then discuss the role of metaplasticity, a homeostatic mechanism of the brain to regulate plasticity changes, in helping to drive neurorehabilitation. Finally, a hypothesis on how metaplasticity could be applied in dysphagia rehabilitation to enhance treatment outcomes is proposed.

Detection of muscle fatigue caused by repeated posterior tongue lift movement from neck surface EMG: a pilot study

BACKGROUND

Fatigue is an important factor for muscle strengthening in rehabilitation medicine. Frequency analysis has been regarded as the gold standard for muscle fatigue assessment in surface electromyography (EMG). However, there are no experiments quantifying fatigue with grouped discharge (GD), which is one of the historical phenomena observed in patients having fatigue, by using high sampling rate recording of EMG.

OBJECTIVE

To investigate the effect of fatigue, which is induced by repeated posterior tongue lift movement (TLM), on the occurrence of GD peaks, thus, to provide possible basis as a parameter for future fatigue evaluation.

METHODS

Nineteen healthy adults (9 men and 10 women) participated in this study. The muscle fatigue protocol consisted of repetitive posterior TLM and maximum voluntary contractions (MVC). Bilateral N-EMG (Neck surface EMG for measuring the muscle activity of the posterior tongue) was recorded.

RESULTS

Subjective tongue fatigue at the end of the protocol was significantly higher than at beginning throughout the muscle fatigue protocol (p < .01). The frequency of occurrence of GD peaks was 0.9 ± 1.2 (per second) at the baseline in 33 of 38 subject sides, and significantly increased depending on fatigue progression (p < .01).

CONCLUSION

It was shown that fatigue due to repetitive posterior tongue lifting resulted in significant increase in the frequency of occurrence of GD peaks. Especially, the nature of GD, showing very few occurrences at non-fatigue condition, might work as an advantageous property for its use in future absolute evaluation of fatigue phenomena.

Questionnaire survey on pharyngolaryngeal sensation evaluation regarding dysphagia in Japan

OBJECTIVE

The objective is to conduct a questionnaire survey regarding pharyngolaryngeal sensation evaluation in dysphagia to understand the current situation in Japan.

METHOD

The questionnaire was sent to the councilor of the Society of Swallowing and Dysphagia of Japan and the Japanese Society of Dysphagia Rehabilitation-Certified Clinician. The prospective questionnaire survey included the questions listed below: Q1: What do you think of the importance of pharyngolaryngeal sensory evaluation? Q2: Select one of the essential swallowing sensations. Q3: Select one of the following regarding the frequency of sensory examination of the larynx. Q4: Select the proportion of cases the sensory test results affect. Q5: As a pharyngolaryngeal sensory evaluation method in swallowing function evaluation, please fill in the table below for the frequency, difficulty, and effectiveness of the following tests, such as gag reflex, touching the larynx by endoscopy, touching the larynx by the probe with endoscopy, cough reflex test, swallowing provocation test.

RESULTS

The essential swallowing sensations of mechanical stimulation, chemical stimulation, thermal stimulation were 84.9%, 5.4%, and 9.7%, respectively. The frequency of touching the larynx by endoscopy in the otolaryngology group and cough reflex test in dentistry was significantly higher than the other groups (p < 0.05). The correlation between the frequency and difficulty or effectiveness of the sensory tests indicated that the frequency and difficulty are significantly correlated between each item.

CONCLUSION

Our results aid in increasing understanding and selection of pharyngolaryngeal sensation evaluation for dysphagia patients.