Coordination of Respiration, Swallowing, and Chewing in Healthy Young Adults

Revealing Goal-Directed Neural Control of the Pharyngeal Phase of Swallowing

Swallowing is considered a three-phase mechanism involving the oral, pharyngeal, and esophageal phases. The pharyngeal phase relies on highly coordinated movements in the pharynx and larynx to move food through the aerodigestive crossing. While the brainstem has been identified as the primary control center for the pharyngeal phase of swallowing, existing evidence suggests that the higher brain regions can contribute to controlling the pharyngeal phase of swallowing to match the motor response to the current context and task at hand. This suggests that the pharyngeal phase of swallowing cannot be exclusively reflexive or voluntary but can be regulated by the two neural controlling systems, goal-directed and non-goal-directed. This capability allows the pharyngeal phase of swallowing to adjust appropriately based on cognitive input, learned knowledge, and predictions. This paper reviews existing evidence and accordingly develops a novel perspective to explain these capabilities of the pharyngeal phase of swallowing. This paper aims (1) to integrate and comprehend the neurophysiological mechanisms involved in the pharyngeal phase of swallowing, (2) to explore the reflexive (non-goal-directed) and voluntary (goal-directed) neural systems of controlling the pharyngeal phase of swallowing, (3) to provide a clinical translation regarding the pathologies of these two systems, and (4) to highlight the existing gaps in this area that require attention in future research. This paper, in particular, aims to explore the complex neurophysiology of the pharyngeal phase of swallowing, as its breakdown can lead to serious consequences such as aspiration pneumonia or death.

Functional involvement of the sternohyoid muscle during breathing and swallowing in rats

The sternohyoid muscle depresses the hyoid bone, but it is unclear whether the muscle contributes to respiratory and swallowing mechanisms. This study aimed to clarify whether the sternohyoid muscle participates in the respiration and swallowing reflex and how the activity is modulated in two conditions: with airway stenosis and with a fixed sternohyoid muscle length. Electromyographic activity in the sternohyoid, digastric, thyrohyoid, and diaphragm muscles was recorded in anesthetized rats. The sternohyoid muscle activity was observed in the inspiratory phase and during swallowing, and was well coordinated with digastric and thyrohyoid muscle activity. With airway stenosis, the respiratory activity per respiratory cycle was facilitated in all assessed muscles but the facilitation of activity per second occurred only in the digastric, thyrohyoid, and sternohyoid muscles. With airway stenosis, the swallowing activity was facilitated only in the digastric muscle but not in the thyrohyoid and sternohyoid muscles. Swallowing activity was not observed in the sternohyoid muscle in the condition with the sternohyoid muscle length fixed, although increased inspiratory activity remained. The current results suggest that 1) the sternohyoid muscle is slightly activated in the inspiratory phase, 2) the effect of airway stenosis on respiratory function may differ between the upper airway muscles and diaphragm, and 3) swallowing activity in the sternohyoid muscle is not dominantly controlled by the swallowing central pattern generator but instead occurs as a myotatic reflex.NEW & NOTEWORTHY We found that the sternohyoid muscle was activated in the inspiratory phase. However, increased airway resistance had different effects on the extrathoracic muscles than on the diaphragm. The swallowing activity of the sternohyoid disappeared when the muscle length was fixed. These findings suggest that the sternohyoid muscle may be activated not by the swallowing central pattern generator but as a myotatic reflex.

Coordination Between Respiration and Swallowing in Patients With Dysphagia After Cervical Spinal Cord Injury: An Observational Case-Control Study

PURPOSE

The purpose of the present study was to characterize the differences between respiration and swallowing in patients with dysphagia after cervical spinal cord injury (CSCI) and to explore the underlying physiological changes.

METHOD

A total of 95 participants were recruited for bedside swallowing evaluation followed by a flexible endoscopic evaluation of swallowing and surface electromyography with a thermocouple nasal airflow sensor examination: 32 with dysphagia, 33 without dysphagia, and 30 healthy controls. The differences in respiratory patterns, swallowing apnea duration (SAD), inspiratory-expiratory ratio, and swallowing efficiency were observed among healthy adults, CSCI patients with and without dysphagia after CSCI.

RESULTS

Compared with those of healthy controls and patients without dysphagia after CSCI, the postswallow respiratory pattern of patients with dysphagia after CSCI was an inspiratory pattern, and the SAD was significantly shorter in patients with dysphagia after CSCI (p < .001). Additionally, the expiratory time in patients with dysphagia was significantly shorter than the inspiratory time, and the swallowing efficiency was reduced, requiring multiple swallows. Moreover, the index of SAD was statistically significant for predicting the development of dysphagia in patients with CSCI (p < .001).

CONCLUSION

Patients with CSCI have an inspiratory pattern after swallowing, and the SAD is significantly reduced; SAD can be used as the predictor of dysphagia in patients after CSCI; the pattern of coordination between respiration and swallowing in patients with dysphagia after CSCI is different from that of healthy controls and patients without dysphagia after CSCI.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.26524717.

Impact of salivary flow inhibition on masticatory behaviours in healthy individuals

BACKGROUND

It remains unclear how the salivary flow and the fat content of food affect bolus formation during mastication.

OBJECTIVES

We aimed to clarify: (1) how hyposalivation affects jaw-closing and hyoid-elevating muscle activities in bolus formation, and (2) if the effect of hyposalivation on muscle activity depends on the fat content of food.

METHODS

Eighteen healthy male volunteers were instructed to freely ingest four test foods: Plain, Fat without seasoning, Fat with seasoning, and Soft rice crackers. Masseter and suprahyoid electromyographic activities were recorded before and 30 min after the administration of atropine sulfate, a muscarinic receptor antagonist that induces hyposalivation.

RESULTS

Hyposalivation extended the masticatory duration significantly in all the test foods except Fat with seasoning. Masticatory cycle time was significantly longer with vs without hyposalivation for the Soft (p = .011). Suprahyoid activity/cycle was significantly greater with vs without hyposalivation (p = .013). Masticatory cycle time was significantly longer at the late stage with vs without hyposalivation for the Soft (p < .001). Suprahyoid activity/cycle was significantly greater at the middle (p = .045) and late stages (p = .002) with vs without hyposalivation for the Soft and greater at the late stage with vs without hyposalivation for the Plain (p = .043). Changes in masticatory cycle time and suprahyoid activity/cycle for these foods had significantly positive relationship (p < .001).

CONCLUSION

Hyposalivation-induced changes in masticatory behaviours resulted from the middle and late stage suprahyoid activity. Fat content and seasoning compensate for salivary flow inhibition.

Neuropeptide Modulation Enables Biphasic Internetwork Coordination via a Dual-Network Neuron

Linked rhythmic behaviors, such as respiration/locomotion or swallowing/chewing, often require coordination for proper function. Despite its prevalence, the cellular mechanisms controlling coordination of the underlying neural networks remain undetermined in most systems. We use the stomatogastric nervous system of the crab Cancer borealis to investigate mechanisms of internetwork coordination, due to its small, well-characterized feeding-related networks (gastric mill [chewing, ∼0.1 Hz]; pyloric [filtering food, ∼1 Hz]). Here, we investigate coordination between these networks during the Gly1-SIFamide neuropeptide modulatory state. Gly1-SIFamide activates a unique triphasic gastric mill rhythm in which the typically pyloric-only LPG neuron generates dual pyloric-plus gastric mill-timed oscillations. Additionally, the pyloric rhythm exhibits shorter cycles during gastric mill rhythm-timed LPG bursts, and longer cycles during IC, or IC plus LG gastric mill neuron bursts. Photoinactivation revealed that LPG is necessary to shorten pyloric cycle period, likely through its rectified electrical coupling to pyloric pacemaker neurons. Hyperpolarizing current injections demonstrated that although LG bursting enables IC bursts, only gastric mill rhythm bursts in IC are necessary to prolong the pyloric cycle period. Surprisingly, LPG photoinactivation also eliminated prolonged pyloric cycles, without changing IC firing frequency or gastric mill burst duration, suggesting that pyloric cycles are prolonged via IC synaptic inhibition of LPG, which indirectly slows the pyloric pacemakers via electrical coupling. Thus, the same dual-network neuron directly conveys excitation from its endogenous bursting and indirectly funnels synaptic inhibition to enable one network to alternately decrease and increase the cycle period of a related network.

The voice and swallowing profile of adults with laryngotracheal stenosis before and after reconstructive surgery: A prospective, descriptive observational study

OBJECTIVES

Airway reconstruction for laryngo tracheal stenosis (LTS) improves dyspnoea. There is little evidence relating to impact upon voice and swallowing. We explored voice and swallowing outcomes in adults with LTS before and after reconstructive surgery.

DESIGN

Outcome measures were collected pre-reconstructive surgery, two-weeks post-surgery and up to 4-6 months post-surgery.

SETTING

Tertiary referral centre.

PARTICIPANTS

With ethical approval, twenty consecutive adult (≥18 years) LTS patients undergoing airway reconstruction were prospectively recruited.

MAIN OUTCOME MEASURES

These included physiological values (maximum phonation time (MPT) and fundamental frequency; penetration aspiration score, residue score), clinician-reported (GRBAS, functional oral intake score, 100ml Water Swallow Test) and patient-reported outcomes (Voice Handicap Index-10, Reflux Symptoms Index, Eating Assessment Tool, Dysphagia Handicap Index).

RESULTS

The observational study identified patient-reported and clinician-reported voice and swallow difficulties pre- and post-surgery; median and interquartile range are reported at each time point: Voice Handicap Index-10 23 (8-31); 20.5 (9-33.5), 24.5 (12.5-29); Dysphagia Handicap Index 9 (0-37); 13 (7-44); 15 (4-34); GRBAS grade 1(1-2); 2 (1-2.5); 2(1-2); 100ml Water Swallow Test volume score 16.7 (11.1-20); 14.3 (12.5-16.7); 16.7 (14.3-20.0); 100ml Water Swallow Test capacity score 16.3 ± 9.0; 11.0 ± 4.1; 12.5 ± 2.6.

CONCLUSIONS

We present the first prospective data on voice and swallowing outcomes in adults with LTS before and after reconstructive surgery. The variability of the outcomes was higher than expected but importantly, for many the voice and swallow outcomes were not within normal limits before surgery. The clinical value of the study demonstrates the need for individual assessment and management of LTS patients' voice and swallowing.

Study on predictive models for swallowing risk in patients with AECOPD

BACKGROUND

Dysphagia is considered a complication in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). However, AECOPD may have risk factors for dysphagia.

METHODS

Through a cross-sectional study, which included 100 patients with AECOPD. General information, Pulmonary function, COPD assessment test (CAT) and modified Medical Research Council (mMRC) were collected by questionnaire. The questionnaires were administered by uniform-trained investigators using standard and neutral language, and swallowing risk was assessed by using a water swallow test (WST) on the day of patient admission.

RESULTS

Among the 100 included patients, 50(50%) were at risk of swallowing. Multivariate analysis using logistic regression analysis showed that age ≥ 74 years old, mMRC ≥ level 2, hospitalization days ≥ 7 days and the use of BIPAP assisted ventilation were important influencing factors for swallowing risk in patients with AECOPD.

CONCLUSION

Patients with AECOPD are at risk for dysphagia, assessing age, mMRC, hospitalization days and the use of BIPAP assisted ventilation can be used to screen for swallowing risk, thus contributing to the implementation of early prevention measures.

Research hotspots and frontiers in post-stroke dysphagia: a bibliometric analysis study

Background

Dysphagia is a common complication of stroke that can result in serious consequences. In recent years, more and more papers on post-stroke dysphagia have been published in various journals. However, there is still a lack of bibliometric analysis of post-stroke dysphagia. This study visually analyzes the global research situation of post-stroke dysphagia from 2013 to 2022, aiming to explore the current research status, frontier trends, and research hotspots in this field.

Methods

Articles and reviews relevant to post-stroke dysphagia were obtained and retrieved from the Web of Science core collection database in the last 10 years (from 2013 to 2022). CiteSpace and Microsoft Excel 2019 were used for bibliographic analysis.

Results

A total of 1,447 articles were included in the analysis. The number of publications showed an overall upward trend, from 72 in 2013 to 262 in 2022. The most influential authors, institutions, journals, and countries were Hamdy S, University of London, Dysphagia, and the People's Republic of China. An analysis of keywords and the literature indicated that current studies in the field of post-stroke dysphagia focused on dysphagia and aspiration, dysphagia classification, dysphagia rehabilitation, and daily living.

Conclusion

This bibliometric analysis reveals the latest advancements and emerging trends in the field of post-stroke dysphagia, spanning the years 2013 to 2022. It highlights the paramount importance of conducting large-scale randomized controlled trials examining the efficacy of dysphagia screening protocols and non-invasive intervention techniques in improving the quality of life for these patients. Such research efforts hold significant academic implications for the development of evidence-based treatment strategies in this field.

Tongue, palatal, hyoid and pharyngeal muscle activity during chewing, swallowing, and respiration

OBJECTIVE

Chewing, swallowing, and respiration are synchronized oropharyngeal functions. This study aimed to analyze the dynamics and coordination during natural chewing and swallowing in relation to respiratory phases.

DESIGN

Eight oropharyngeal muscles in minipigs were recorded using electromyography, X-ray fluoroscopy, and nasopharyngeal dynamics. Chewing cycles and swallowing episodes were analyzed for timing and activity amplitude along respiratory cycles. Digastric and middle pharyngeal constrictor were used as zero-points for timing analysis in chewing cycles and swallowing episodes, respectively. The beginning of these cycles and episodes were used as the zero-point for timing analysis in respiration during feeding.

RESULTS

The timing of jaw closing (57.8%) was longer than opening (42.2%) during chewing. Muscle activity occurred 20% later than digastric onsets and 15% earlier than jaw closing phase. Duration of muscle activity was shorter in ipsilateral than contralateral sides except for palatal muscles. Pharyngeal, palatal, and hyoid muscles showed longer durations than tongue muscles in jaw opening (p < 0.05). Palatal and hyoid muscles showed 2-phased activity in chewing while hyoid muscles showed higher amplitude in chewing and swallowing than other muscles. About 80% of the chewing cycles and swallowing episodes occurred in expiration. Nasopharyngeal airflow velocity increased from jaw opening to swallowing while airflow pressure decreased.

CONCLUSION

These findings indicate key activity of palatal and pharyngeal muscles mostly in chewing. The respiratory cycle changes in chewing and swallowing simultaneously with the activation of the tongue, palatal, and pharyngeal muscles. These findings will be useful for further understanding the mechanisms in swallowing and breathing disorders.

Association between Bone Mineral Density and Oral Frailty on Renal Function: Findings from the Shika Study

The association between oral frailty (OFr) and body action has been investigated, but its association with systemic function remains unclear. Therefore, this cross-sectional study examined the association between OFr with decreased bone mineral density (BMD) and renal function in residents of Shika town, Ishikawa Prefecture, Japan aged ≥40 years. This study included 400 inhabitants. The OFr total score was assessed using three oral domains in the Kihon Checklist (a self-reported comprehensive health checklist), the number of teeth, and brushing frequency per day. Measurements were the estimated glomerular filtration rate (eGFR) and the osteo-sono assessment index (OSI). Using a two-way analysis of covariance (p = 0.002), significantly lower OSI was indicated in the eGFR < 60 and OFr group than in the eGFR of < 60 and non-OFr group after adjusting for age, body mass index, and drinking and smoking status as confounding factors. Multiple logistic regression analysis confirmed this relationship (p = 0.006). Therefore, lower BMD seems to be associated with lower renal function only when accompanied by OFr. Further longitudinal studies are needed to confirm these results.

Pilot Study of Respiratory-Swallow Coordination in Amyotrophic Lateral Sclerosis

PURPOSE

Amyotrophic lateral sclerosis (ALS) impacts bulbar and respiratory musculature, which may contribute to impaired swallow function (dysphagia) and respiratory-swallow coordination. The purpose of this pilot study was to examine if respiratory-swallow coordination in individuals with ALS was perturbed compared to healthy controls. We further explored relationships between measures of respiratory function and self-reported swallowing outcomes on respiratory-swallow coordination.

METHOD

We employed a cross-sectional design with eight participants with ALS and eight age- and sex-matched healthy participants. Respiratory inductance plethysmography and a nasal cannula were used to capture respiratory-swallow phase patterns during a standardized clinical swallow examination. The advantageous respiratory-swallow phase pattern was defined if exhalation surrounded the swallow (E-E). Spirometry was used to capture indices of respiratory function (forced vital capacity % predicted, peak cough flow [PCF]). Validated questionnaires were used to collect information regarding ALS-related bulbar functional status and swallowing-related concerns.

RESULTS

Compared to the matched healthy cohort, individuals with ALS demonstrated higher rates of non-E-E respiratory-swallow phase patterning and worse bulbar/swallow dysfunction. Group (ALS), swallow tasks, and PCF were significantly associated with respiratory-swallow phase pattern.

CONCLUSIONS

These preliminary findings support altered respiratory-swallow phase patterning in ALS. Future work should employ an instrumental assessment to quantify swallowing physiology and elucidate the relationship between perturbed respiratory-swallow coordination and swallowing function.