Volitional control of food transport and bolus formation during feeding

Difference in the Electromyographic Behavior of the Masticatory and Swallowing Muscles During Cued Versus Spontaneous Swallowing

The risk of dysphagia and/or aspiration is determined using screening tests, such as the repeated saliva swallowing test and modified water swallowing test, which evaluate cued swallowing. However, humans masticate and swallow foods with various consistencies, forms, and amounts, without conscious awareness. Therefore, this study aimed to examine the difference in the behavior of masticatory and swallowing muscles during spontaneous versus cued swallowing through a series of mastication and swallowing processes by evaluating surface electromyogram (sEMG) signals. The effect of the consistency and amount of food on the behavior of these muscles was also investigated. The sEMG recordings of the masseter muscles and anterior belly of the digastric muscle for 12 subjects, and genioglossus muscle for 5 subjects were obtained. The genioglossus activity was recorded using custom-made ball electrodes. The test foods were cookies and tofu, in amounts of 2 g and 4 g. The normalized muscle activity (integrated EMG), duration of the muscle activity, initial activation timepoint of each muscle, and total duration of swallowing were compared among four conditions. The activity of each muscle was significantly higher during the swallowing of cookies than tofu, for 4 g vs 2 g, and for cued versus spontaneous swallowing. The duration of each muscle activity, initial activation timepoint, and total duration of swallowing were significantly longer for cookies versus tofu, for 4 g vs 2 g, and for spontaneous versus cued swallowing. These results suggest that the behavior of the masticatory and swallowing muscles is affected by cued swallowing and by the consistency and amount of food.

Chewing Well Modulates Pharyngeal Bolus Transit During Swallowing in Healthy Participants

Mastication is controlled by central pattern generator in the brainstem and can be modulated by volition. The aim of this study was to investigate the effect of chewing well on swallowing. Twenty-six healthy participants were instructed to eat 8, 12, and/or 16 g of steamed rice with barium sulphate under the following two conditions: chewing freely task (CF; chewing naturally in their usual manner) and chewing well task (CW; chewing the food with a request to "chew well"). We evaluated bolus transport and swallowing movement using videofluoroscopy and electromyography of the masseter, suprahyoid and thyrohyoid muscles. The chewing time and pharyngeal transit time (PTT) at the first swallow showed high reproducibility in both CF and CW. PTT for CW was significantly shorter and longer than CF in 12 and 16 g, respectively. In 12 g, CW increased the pharyngeal bolus velocity and decreased thyrohyoid EMG activity during swallowing compared with CF. In 16 g, the difference between CW and CF in the estimated swallowed bolus volume was positively correlated with that in upper esophageal sphincter transit duration. We speculate that CW modulates PTT during swallowing depending on the mouthful volume.

Links Between Swallowing and Consciousness: A Narrative Review

This literature review explores a wide range of themes addressing the links between swallowing and consciousness. Signs of consciousness are historically based on the principle of differentiating reflexive from volitional behaviors. We show that the sequencing of the components of swallowing falls on a continuum of voluntary to reflex behaviors and we describe several types of volitional and non-volitional swallowing tasks. The frequency, speed of initiation of the swallowing reflex, efficacy of the pharyngeal phase of swallowing and coordination between respiration and swallowing are influenced by the level of consciousness during non-pathological modifications of consciousness such as sleep and general anesthesia. In patients with severe brain injury, the level of consciousness is associated with several components related to swallowing, such as the possibility of extubation, risk of pneumonia, type of feeding or components directly related to swallowing such as oral or pharyngeal abnormalities. Based on our theoretical and empirical analysis, the efficacy of the oral phase and the ability to receive exclusive oral feeding seem to be the most robust signs of consciousness related to swallowing in patients with disorders of consciousness. Components of the pharyngeal phase (in terms of abilities of saliva management) and evoked cough may be influenced by consciousness, but further studies are necessary to determine if they constitute signs of consciousness as such or only cortically mediated behaviors. This review also highlights the critical lack of tools and techniques to assess and treat dysphagia in patients with disorders of consciousness.

Swallowing Functions after Sagittal Split Ramus Osteotomy with Loose Fixation for Mandibular Prognathism: A Retrospective Case Series Research

Sagittal split ramus osteotomy (SSRO) is a standard surgical technique for patients with mandibular prognathism. However, the appropriate position of the proximal fragment is not strictly defined, and rigid fixation can induce early postoperative skeletal relapse and temporomandibular (TMJ) disorders. Loose fixation can be expected to seat the proximal bone fragments in a physiologically appropriate position, thereby reducing adverse events. Although long-term skeletal stability has been achieved using SSRO without fixation, the evaluation of preoperative and postoperative eating and swallowing functions remains unclear, and this study aimed to clarify this point. We evaluated mastication time, oral transfer time, and pharyngeal transfer time using videofluorography (VF) preoperatively, two months postoperatively, and six months postoperatively, and along with the position of anatomical landmarks using cephalometric radiographs, modified water swallowing test (MWST), food test (FT), and repetitive saliva swallowing test (RSST) were used to evaluate postoperative swallowing function. Four patients (one male, three females; mean (range) age 26.5 (18-51) years) were included, with a mean setback of 9.5 mm and 6.5 mm on the right and left sides, respectively. Postoperative eating and swallowing functions were good in VF, cephalometric analysis, MWST, FT, and RSST. In the present study, good results for postoperative eating and swallowing functions were obtained in SSRO with loose fixation of the proximal and distal bone segments.

Phenotypic expression of swallowing function in Niemann-Pick disease type C1

Background

Niemann–Pick disease type C1 (NPC1) is a rare autosomal recessive disease characterized by endolysosomal accumulation of unesterified cholesterol with progressive deterioration in swallowing, often leading to premature death. Although documented, the natural history of NPC1 swallowing dysfunction has yet to be delineated systematically. This manuscript aims to provide a comprehensive characterization of the phenotypic spectrum and progression of swallowing dysfunction in NPC1.

Methodology

The National Institutes of Health (NIH) NPC1 natural history study (NCT00344331) enrolled 120 patients, who underwent comprehensive interpretative swallow assessments for swallowing safety, dietary modifications, and aspiration risk. Longitudinal statistical modeling accounted for all outcomes with NPC1 disease covariates (first symptom onset, age at neurological symptom onset, seizure history, duration of neurological symptoms) as well as miglustat use (a glucosylceramide synthase inhibitor) and NIH study duration (NIHSD; the length of time an individual participated in the NIH study). Probabilities for disease progression and time to swallowing decline were conducted for the entire cohort.

Results

Time to swallowing decline with American Speech-Language-Hearing Association National Outcome Measure (ASHA-NOMS) and the NIH-adapted Penetration Aspiration Scale (NIH-PAS) were identified: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\frac{7.7}{100}$$\end{document}7.7100 person-years and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\frac{9.8}{100}$$\end{document}9.8100 person-years, respectively. NIHSD and seizure history consistently and significantly were associated with decline (OR_NIHSD = 1.34–2.10, 95% CI 1.04–3.4, p = 0.001–0.026; OR_Seizure = 3.26–18.22, 1.03–167.79; p = 0.001–0.046), while miglustat use revealed protection (OR_Miglustat = 0.01–0.43, 0.007–0.98; p = 0.001–0.044). The probability of decline with NPC1 neurological severity scale and annual severity increment scale were established with the aforementioned covariates, varying amongst subgroups.

Conclusion

This study represents the most extensive collection of prospective, instrumental swallowing assessments in NPC1 to date with an interpretive analysis providing an improved understanding of NPC1 disease progression with swallowing function—serving as a foundation for clinical management and future NPC1 therapeutics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02472-w.

Visuoperceptual Analysis of the Videofluoroscopic Study of Swallowing: An International Delphi Study

INTRODUCTION

The Videofluoroscopic Swallow Study (VFSS) is a commonly used dysphagia assessment that is routinely analysed visuoperceptually. However, no consensus exists regarding which visuoperceptual measures should be used to analyse VFSSs. Current visuoperceptual measures for VFSSs are limited by poor quality and incomplete or indeterminate psychometric properties.

OBJECTIVE

This study aimed to establish the content validity for a new visuoperceptual VFSS measure for oropharyngeal dysphagia in adults, by identifying relevant domains of the construct and generating items and corresponding response scales.

METHODS

Consensus among experts in dysphagia and VFSS from over 20 countries was achieved across three rounds of anonymous online surveys, using the Delphi technique. Participants judged relevance and comprehensiveness of definitions of visuoperceptual domains of VFSS and the relevance of various domains to the overall construct. After reaching consensus on definitions of relevant domains, consensus on items were established using the same process.

RESULTS

Participants achieved consensus on definitions of 32 domains recommended for analysis, and at least one item per domain (range 1-4). Domains selected by participants included both those which occur in existing measures and domains which have not been included in any measures to date. This study will form the basis for content validity of a new measure for VFSS.

CONCLUSIONS

This first phase of developing a visuoperceptual measure of VFSS resulted in the identification of 32 domains and 60 items for oropharyngeal dysphagia. Developers can now advance to the next phase of measure construction; prototype development and psychometric testing.

The influence of thickeners of food on the particle size of boluses: a consideration for swallowing

The purpose of this study was to examine the influence of thickeners with different levels of thickness on the sizes of particles in food boluses. In medical and nursing care, thickeners are used to make food safe for patients with dysphagia. However, the effect of thickeners on the foods they are added to, especially during swallowing, is still unclear. The bolus particles of 20 healthy volunteers were photographed, and the digital images were used to estimate the sizes of particles in them. Eight test samples with thickeners with different levels of thickness were tested: six grades of thickened carrot juice with raw carrots in it, raw carrot with banana, and raw carrot alone. The particle homogeneity index (HI) and particle size index (SI) just before swallowing were calculated. The viscosities of the liquid part of the test samples were also measured. The number of mastication cycles across the test samples was not significantly different. However, significant differences were found in SI and HI across the test samples: the absolute values of SI and HI tended to rise as the thickness of the test sample increased. The viscosity of the liquid part of the test sample also increased as the thickness increased. The differences in the thickness of food had an influence on the bolus particle sizes just before swallowing.

Effect of attention on chewing and swallowing behaviors in healthy humans

We examined how attention alters chewing and swallowing behaviors. Twenty-one healthy volunteers were asked to freely eat 8 g of steamed rice in three separate trials, and we obtained the average number of chewing cycles (N) and chewing duration (T) prior to the first swallow in each trial. We also conducted an N-limited test, in which participants chewed the food while independently counting the number of chewing cycles and swallowed the food when they reached N, and a T-limited test, in which they chewed the food for T sec and then swallowed. We recorded electromyograms (EMGs) from masseter and suprahyoid muscles and collected videoendoscopic images. In the N-limited test, chewing speed decreased, masseter muscle activity (area under the curve of the rectified EMG burst) per cycle increased, and suprahyoid muscle activity per cycle decreased. In the T-limited test, the chewing speed increased, muscle activities per cycle decreased, and the number of cycles increased. The occurrence frequency of bolus propulsion into the pharynx before swallowing was smaller in the N- and T-limited tests than in the free chewing test. Further, the whiteout time was longer in the T-limited test than in the free chewing test. Attentional chewing changes not only chewing but also swallowing behavior.

Disruption of the Obligatory Swallowing Sequence in Patients with Wallenberg Syndrome

Although the sequence of events involved in swallowing varies among healthy adults, healthy adults demonstrate some consistent patterns, including opening of the upper esophageal sphincter (UES) prior to maximum laryngeal elevation (LE). Previous animal studies suggested that swallowing is regulated by a neuronal network in the medulla, and lateral medullary infarction, or Wallenberg syndrome, frequently causes dysphagia. This retrospective, observational, multicenter study aimed to determine if the sequence of swallowing events was disturbed in patients with Wallenberg syndrome compared with previously published reference data for healthy adults. The study subjects included 35 patients with Wallenberg syndrome admitted to three hospitals in Japan from 1/4/2009 to 31/3/2017. Sixteen timing events, including maximum LE and UES opening, and the intervals between events were measured. If the sequence of events was the same as in healthy adults, the interval value was positive, and if the sequence of events was opposite to that in healthy adults, the value was negative. The median interval from UES opening to maximum LE was - 0.02 s (range - 0.80 to 0.89, 95% CI - 0.14 to 0.10). About half of the Wallenberg cases showed negative values indicating that the sequence was reversed. These results suggest that lateral medullary infarction impairs the sequence of swallowing events.

High-Resolution Cervical Auscultation Signal Features Reflect Vertical and Horizontal Displacements of the Hyoid Bone During Swallowing

Millions of people across the globe suffer from swallowing difficulties, known as dysphagia, which can lead to malnutrition, pneumonia, and even death. Swallowing cervical auscultation, which has been suggested as a noninvasive screening method for dysphagia, has not been associated yet with any physical events. In this paper, we have compared the hyoid bone displacement extracted from the videofluoroscopy images of 31 swallows to the signal features extracted from the cervical auscultation recordings captured with a tri-axial accelerometer and a microphone. First, the vertical displacement of the anterior part of the hyoid bone is related to the entropy rate of the superior–inferior swallowing vibrations and to the kurtosis of the swallowing sounds. Second, the vertical displacement of the posterior part of the hyoid bone is related to the bandwidth of the medial–lateral swallowing vibrations. Third, the horizontal displacements of the posterior and anterior parts of the hyoid bone are related to the spectral centroid of the superior–inferior swallowing vibrations and to the peak frequency of the medial–lateral swallowing vibrations, respectively. At last, the airway protection scores and the command characteristics were associated with the vertical and horizontal displacements, respectively, of the posterior part of the hyoid bone. Additional associations between the patients’ characteristics and auscultations’ signals were also observed. The hyoid bone maximal displacement is a cause of swallowing vibrations and sounds. High-resolution cervical auscultation may offer a noninvasive alternative for dysphagia screening and additional diagnostic information.

Swallowing Kinematic Differences Across Frozen, Mixed, and Ultrathin Liquid Boluses in Healthy Adults: Age, Sex, and Normal Variability

PURPOSE

The aim of this study was to examine the effects of frozen and mixed-consistency boluses on the swallowing physiology of younger and older adults. We also aimed to quantify factors that lead to increased variability in swallowing outcomes (i.e., age, sex, bolus type).

METHOD

Forty-one healthy adults (18-85 years old) swallowed 5 blocks of 5 different boluses: 10-ml ultrathin liquid, a teaspoon of iced barium, a teaspoon of room-temperature pudding, a teaspoon of frozen pudding, and ultrathin barium with chocolate chips. All data were recorded with videofluoroscopy and underwent detailed timing kinematic measurements.

RESULTS

Neither barium ice nor frozen pudding sped up swallow responses. Many healthy adults initiated swallowing with the bolus as deep as the pyriform sinuses. Swallowing temporal kinematics for ultrathin liquid consistencies are most different from all others tested, requiring the best possible physiological swallowing performance in younger and older healthy individuals (i.e., faster reaction times, longer durations) compared with other bolus types tested. In each measure, older adults had significantly longer durations compared with the younger adults. More variability in swallowing kinematics were seen with age and laryngeal vestibule kinematics.

CONCLUSION

This study provides important contributions to the literature by clarifying normal variability within a wide range of swallowing behaviors and by providing normative data from which to compare disordered populations.

The influence of tongue strength on oral viscosity discrimination acuity

The ability to generate tongue pressures is widely considered to be critical for liquid bolus propulsion in swallowing. It has been proposed that the application of tongue pressure may also serve the function of collecting sensory information regarding bolus viscosity (resistance to flow). In this study, we explored the impact of age-related reductions in tongue strength on oral viscosity discrimination acuity. The experiment employed a triangle test discrimination protocol with an array of xanthan-gum thickened liquids in the mildly to moderately thick consistency range. A sample of 346 healthy volunteers was recruited, with age ranging from 12 to 86 (164 men, 182 women). On average, participants were able to detect a 0.29-fold increase in xanthan-gum concentration, corresponding to a 0.5-fold increase in viscosity at 50/s. Despite having significantly reduced tongue strength on maximum isometric tongue-palate pressure tasks, and regardless of sex, older participants in this study showed no reductions in viscosity discrimination acuity.

PRACTICAL APPLICATIONS

In this article, the relationship between tongue strength and the ability to discriminate small differences in liquid viscosity during oral processing is explored. Given that tongue strength declines with age in healthy adults and is also reduced in individuals with dysphagia, it is interesting to determine whether reduced tongue strength might contribute to difficulties in evaluating liquid viscosity during the oral stage of swallowing. Using an array of mildly to moderately thick xanthan-gum thickened liquids, this experiment failed to find any evidence that reductions in tongue strength influence oral viscosity discrimination acuity.

The Test of Masticating and Swallowing Solids (TOMASS): reliability, validity and international normative data

BACKGROUND

Clinical swallowing assessment is largely limited to qualitative assessment of behavioural observations. There are limited quantitative data that can be compared with a healthy population for identification of impairment. The Test of Masticating and Swallowing Solids (TOMASS) was developed as a quantitative assessment of solid bolus ingestion.

AIMS

This research programme investigated test development indices and established normative data for the TOMASS to support translation to clinical dysphagia assessment.

METHODS & PROCEDURES

A total of 228 healthy adults (ages 20-80+ years) stratified by age and sex participated in one or more of four consecutive studies evaluating test-retest and interrater reliability and validity to instrumental assessment. For each study the test required participants to ingest a commercially available cracker with instructions to 'eat this as quickly as is comfortably possible'. Further averaged measures were derived including the number of masticatory cycles and swallows per bite, and time per bite, masticatory cycle and swallow. Initial analyses identified significant differences on salient measures between two commercially available crackers that are nearly identical in shape, size and ingredients, suggesting the need for separate normative samples for specific regional products. Additional analyses on a single cracker identified that the TOMASS was sensitive at detecting changes in performance based on age and sex. Test-retest reliability across days and interrater reliability between clinicians was high, as was validation of observational measures to instrumental correlates of the same behaviours. Therefore, normative data are provided for the TOMASS from a minimum of 80 healthy controls, stratified by age and sex, for each of seven commercially available crackers from broad regions worldwide.

OUTCOMES & RESULTS

Analyses on a single cracker identified Arnott's Salada, and that TOMASS measures were sensitive for detecting changes in performance based on age and sex. Interrater and test-retest reliability across days were high, as was validation of observational measures to instrumental correlates of the same behaviours. Significant differences were identified between two commercially available crackers, nearly identical in shape, size and ingredients, thus normative samples for specific regional products were required. Normative data were then acquired for the TOMASS from a minimum of 80 healthy controls, stratified by age and sex, for each of seven commercially available crackers from broad regions worldwide.

CONCLUSIONS & IMPLICATIONS

The TOMASS is presented as a valid, reliable and broadly normed clinical assessment of solid bolus ingestion. Clinical application may help identify dysphagic patients at bedside and provide a non-invasive, but sensitive, measure of functional change in swallowing.

Normal Muscular Activity during Swallowing as Measured by Surface Electromyography

Objectives

Speech-language pathologists use surface electromyography biofeedback as a tool to facilitate swallowing treatment, particularly to improve swallowing strength and coordination. The present study sought to establish normative data of swallowing muscular activity as measured by surface electrodes in order to compare the performance of patients with dysphagia to normal swallow performance.

Methods

Thirty normal young (18 to 25 years of age) and elderly (60 or more years of age) subjects swallowed 3 bolus volumes (5, 10, and 20 mL) in 2 conditions: swallow-to-command and swallow-when-ready. Swallow muscular activity was measured in microvolts with a portable biofeedback unit.

Results

There were significant differences between the 2 swallowing conditions in both age groups. Neither age nor bolus volume had a significant effect on the findings.

Conclusions

In using surface electromyography biofeedback as an adjunct to swallowing rehabilitation, it may be more beneficial to use swallow-to-command techniques if one is interested in measuring maximum effort, regardless of patient age or volume selected.

Food transit duration is associated with the number of stage II transport cycles when eating solid food

OBJECTIVE

When eating solids, stage II transport (St2Tr) propels triturated food into the pharynx for bolus formation and storage before swallowing. Although the existence of St2Tr is acknowledged, the reason for its existence remains unclear. Understanding it may facilitate development of food appropriate for individuals with dysphagia. The purpose of this study was to explore how measures of duration of eating and swallowing affect the number of St2Tr cycles.

DESIGN

Videofluorography was performed on 13 healthy subjects eating 6-g squares of banana, tofu, and cookies. Measurements included the number of St2Tr cycles, duration of processing (from food entering the mouth to onset of swallowing), pre-upper esophageal sphincter (UES) transit duration (from onset of swallowing to onset of UES transit), UES transit duration (leading edge to trailing edge passing the UES), and total sequence duration (from onset of swallowing to terminal swallow). Principal component (PC) analysis was used to identify factors affecting the number of St2Tr cycles. Analysis of covariance was performed using the 1st PC as an independent variable for predicting the number of St2Tr cycles.

RESULTS

All four duration measures were significantly positively correlated with the number of St2Tr cycles. Analysis revealed two orthogonal PCs with variable loading. The 1st PC was a function of the timing variables. The 2nd PC was a function of the number of swallows.

CONCLUSIONS

The number of St2Tr cycles was associated with measures of food transit duration and was greater with harder foods before processing and more viscous foods just before swallowing.

Onset locations of the pharyngeal phase of swallowing: meta-analysis

Purpose

Literature review on the onset locations of the pharyngeal phase of swallowing in asymptomatic and symptomatic adults and elderly people.

Research strategies

Research was conducted in the PubMed, BIREME and SciELO databases through the descriptors fluoroscopy (fluoroscopia), deglutition (deglutição) and pharynx (faringe).

Selection criteria

Studies published between 2005 and 2015, carried out with adults and elderly people who underwent swallowing videofluoroscopy (SVF), and citing the onset location of the pharyngeal phase of swallowing.

Data analysis

Descriptive analysis and meta-analysis were performed, evaluating the heterogeneity and the measures grouped with random effects through I2 statistics. For ratio calculation in the meta-analysis, the locations described in the articles were classified according to the Modified Barium Swallowing protocol - Measurement Tool for Swallowing Impairment (MBSImp).

Results

Twelve articles were selected for descriptive analysis and seven for meta-analysis. Heterogeneity was found between studies, especially due to clinical and methodological differences. The random effect indicated predominance (58%) of the onset of the pharyngeal phase of swallowing at levels 0 and 1 of the MBSImP. In asymptomatic individuals, the onset of the pharyngeal phase was observed in the oral cavity, base of the tongue, dorsum of the tongue and vallecula. In symptomatic individuals, onset was mainly observed in the oropharynx, vallecula, hypopharynx and pyriform sinus.

Conclusion

We noted a greater frequency of the onset of the pharyngeal phase of swallowing in the vallecula. The onset of the pharyngeal phase in the hypopharynx and pyriform sinus was more often observed among elderly individuals or with comorbidities that could alter swallowing.

Defining the end-point of mastication: A conceptual model

The great risks of swallowing are choking and aspiration of food into the lungs. Both are rare in normal functioning humans, which is remarkable given the diversity of foods and the estimated 10 million swallows performed in a lifetime. Nevertheless, it remains a major challenge to define the food properties that are necessary to ensure a safe swallow. Here, the mouth is viewed as a well-controlled processor where mechanical sensory assessment occurs throughout the occlusion-circulation cycle of mastication. Swallowing is a subsequent action. It is proposed here that, during mastication, temporal maps of interfacial property data are generated, which the central nervous system compares against a series of criteria in order to be sure that the bolus is safe to swallow. To determine these criteria, an engineering hazard analysis tool, alongside an understanding of fluid and particle mechanics, is used to deduce the mechanisms by which food may deposit or become stranded during swallowing. These mechanisms define the food properties that must be avoided. By inverting the thinking, from hazards to ensuring safety, six criteria arise which are necessary for a safe-to-swallow bolus. A new conceptual model is proposed to define when food is safe to swallow during mastication. This significantly advances earlier mouth models.

PRACTICAL APPLICATIONS

The conceptual model proposed in this work provides a framework of decision-making to define when food is safe to swallow. This will be of interest to designers of dietary foods, foods for dysphagia sufferers and will aid the further development of mastication robots for preparation of artificial boluses for digestion research. It enables food designers to influence the swallow-point properties of their products. For example, a product may be designed to satisfy five of the criteria for a safe-to-swallow bolus, which means the sixth criterion and its attendant food properties define the swallow-point. Alongside other organoleptic factors, these properties define the end-point texture and enduring sensory perception of the food.

Fabrication of Artificial Food Bolus for Evaluation of Swallowing

Simple and easy methods to evaluate swallowing are required because of the recently increased need of rehabilitation for dysphagia. "Artificial food bolus", but not "artificial food", would be a valuable tool for swallowing evaluation without considering the mastication effect which is altered according to the individual's oral condition. Thus, this study was carried out to fabricate artificial bolus resembling natural food bolus. The mechanical property and the volume change of food bolus in normal people were firstly investigated. Thirty healthy adults without dysphagia were selected and asked to chew four sample foods (rice cake, peanut, burdock, and gummy candy). The results indicated that Young's modulus of bolus before swallowing was below 150 kPa. The bolus volume before swallowing was below 400 mm3. In addition, the saliva component ratio of each bolus was approximately 30wt%, and the average saliva viscosity of research participants was approximately 10 mPa•s. Based on the obtained data, artificial food bolus was designed and fabricated by using alginate hydrogel as a visco-elastic material and gelatin solution as a viscotic material with a ratio of 7:3 based on weight. Consequently, the swallowing time of fabricated artificial food bolus was measured among the same participants. The results indicated the participants swallowed fabricated food bolus with similar manner reflecting their mechanical property and volume. Thus, this artificial food bolus would be a promising tool for evaluation of swallowing.

Effect of body posture on involuntary swallow in healthy volunteers

Clinically, reclining posture has been reported to reduce risk of aspiration. However, during involuntary swallow in reclining posture, changes in orofacial and pharyngeal movement before and during pharyngeal swallow should be considered. Further, the mechanisms underlying the effect of body posture on involuntary swallow remain unclear. The aim of the present study was to determine the effect of body posture on activity patterns of the suprahyoid muscles and on patterns of bolus transport during a natural involuntary swallow. Thirteen healthy male adults participated in a water infusion test and a chewing test. In the water infusion test, thickened water was delivered into the pharynx at a very slow rate until the first involuntary swallow was evoked. In the chewing test, subjects were asked to eat 10 g of gruel rice. In both tests, the recording was performed at four body postures between upright and supine positions. Results showed that reclining changed the location of the bolus head at the start of swallow and prolonged onset latency of the swallowing initiation. Muscle burst duration and whiteout time measured by videoendoscopy significantly increased with body reclining and prolongation of the falling time. In the chewing test, reclining changed the location of the bolus head at the start of swallow, and the frequency of bolus residue after the first swallow increased. Duration and area of EMG burst and whiteout time significantly increased with body reclining. These data suggest that body reclining may result in prolongation of pharyngeal swallow during involuntary swallow.

Biomechanics of human tongue movement during bolus compression and swallowing

We evaluated the effects of gel consistency and bolus volume on ingestion in humans. Eight healthy men were asked to ingest liquids, and sample foods of different gel consistencies and volumes, as usual. Tongue pressure against the hard palate was recorded at five points, and bolus flow was recorded using videoendoscopic images. The number of squeezes increased as gel consistency and volume increased. The integrated magnitude of tongue pressure during squeezing increased with increasing gel consistency. Bolus propulsion into the pharynx was affected by bolus characteristics, and location of the bolus head at the onset of pharyngeal swallowing was not related to squeezing behavior. The trigger point at which pharyngeal swallowing began was subject-dependent. During swallowing, the magnitude of tongue pressure moderately increased with increasing gel consistency, as compared with squeezing. Tongue pressure was not related to bolus volume. The current results suggest that patterns of tongue pressure during squeezing and swallowing are differentially affected by bolus conditions. However, healthy subjects differed in the techniques used for squeezing and swallowing.

Volitional chewing with a conscious effort alters and facilitates swallowing during feeding sequence

The key objective of mastication is to form a food bolus suitable for smooth swallowing. However, chewing is usually performed without a conscious effort. Poor bolus formation can cause pharyngeal residue and suffocation in elderly individuals with reduced swallowing function. Therefore, chewing with a conscious effort may help the bolus to more easily pass the pharynx. This study aimed to clarify the impact of mastication with a conscious effort on the feeding sequence. Subjects included 25 dentulous volunteers who were informed and provided written consent. Lateral videofluoroscopy was performed during the feeding of solid agar jelly under two conditions: chewing naturally in their usual manner (without volition) and chewing with a conscious effort (with volition). Temporal evaluation was performed for mastication, stage II transport (STII), swallow onset and oropharyngeal transit time. Moreover, bolus volume at swallow onset and subjective evaluation of swallowing easiness were measured. Volitional chewing with a conscious effort lengthened the duration of the chewing sequence before and after STII and delayed the swallow onset despite the fact that the bolus volume in the vallecula and hypopharynx (HYP) had significantly increased. Furthermore, with volition, the bolus transit time from swallow onset in the oral cavity, upper oropharynx and HYP was reduced, and subjective evaluation of swallowing easiness demonstrated significant improvement. These results suggest that volitional chewing with a conscious effort can alter bolus transport and swallowing, resulting in easier swallowing.

Impacts of wearing complete dentures on bolus transport during feeding in elderly edentulous

Prosthetic treatment with dentures is often required for the elderly who have reduced swallowing function. Therefore, it is important to understand the relationship between denture-wearing and feeding function from the perspective of swallowing. To clarify changes in bolus transport during feeding in elderly edentulous patients with or without complete dentures. Subjects were 15 elderly edentulous volunteers who were treated with maxillary and mandibular complete dentures. The test food was 10 g of minced agar jelly containing barium sulphate with a particle diameter of 4·0-5·6 mm. Lateral videofluoroscopy was performed to assess the position of the leading edge of the bolus, the bolus volume in each area at swallow onset, bolus transit time and the mandibular position during pharyngeal swallowing. There were significant changes between the bolus transport with and without dentures. Without dentures, the leading edge of the bolus at swallow onset fell from the valleculae area to the hypopharynx, and the bolus volume in the hypopharynx increased. Bolus transit time increased in the oral cavity, valleculae and hypopharynx. The mandibular position shifted anterosuperior direction. The results arose owing to anatomical changes in the oral and pharyngeal structure and the following functional changes: poor food manipulation, poor bolus formation and delayed swallowing reflex. Removing dentures in elderly edentulous individuals influences bolus transport during feeding, resulting in the exacerbation of the reduced swallowing reserve capacity that accompanies ageing, and may increase the risk of dysphagia.

Videofluoroscopic assessment of pharyngeal stage delay reflects pathophysiology after brain infarction

OBJECTIVES/HYPOTHESIS

The pathophysiology of dysphagia caused by brain infarction varies with the site of the lesion in the brain. Patients with suprabulbar lesions have demonstrated delayed triggering of pharyngeal stage including delayed laryngeal elevation. Patients with severe pharyngeal stage delay have a high risk of intractable aspiration to the lower respiratory tract. Despite this, few studies have compared the pharyngeal stage delay with the lesion site. We defined a new temporal parameter of the pharyngeal stage delay to assess laryngeal elevation delay against the bolus inflow into the pharyngeal space. This study aimed to elucidate whether this parameter of pharyngeal stage delay is clinically useful to assess the pathophysiology of brain lesions after brain infarction.

STUDY DESIGN

Case-control study.

METHODS

Videofluoroscopic assessment of swallowing examinations was performed from January 7, 2000 to March 29, 2011 at Kyushu University Hospital. We evaluated the pharyngeal stage delay using motion analysis on videofluoroscopic swallowing examination in patients with normal swallowing and brain infarction patients divided into pathophysiologic lesion groups. Laryngeal elevation delay time and pharyngeal delay time were analyzed.

RESULTS

Significant differences in laryngeal elevation delay time were observed between each pathophysiologic lesion group. However, pharyngeal delay time remained similar among groups. Brain infarctions of corticobulbar tract and basal ganglion were significantly associated with laryngeal elevation delay time prolongation.

CONCLUSIONS

Laryngeal elevation delay time with low-viscosity contrast medium is a recommended parameter to discriminate the corticobulbar tract and the basal ganglion lesion.

Role of physical bolus properties as sensory inputs in the trigger of swallowing

Background

Swallowing is triggered when a food bolus being prepared by mastication has reached a defined state. However, although this view is consensual and well supported, the physical properties of the swallowable bolus have been under-researched. We tested the hypothesis that measuring bolus physical changes during the masticatory sequence to deglutition would reveal the bolus properties potentially involved in swallowing initiation.

Methods

Twenty normo-dentate young adults were instructed to chew portions of cereal and spit out the boluses at different times in the masticatory sequence. The mechanical properties of the collected boluses were measured by a texture profile analysis test currently used in food science. The median particle size of the boluses was evaluated by sieving. In a simultaneous sensory study, twenty-five other subjects expressed their perception of bolus texture dominating at any mastication time.

Findings

Several physical changes appeared in the food bolus as it was formed during mastication: (1) in rheological terms, bolus hardness rapidly decreased as the masticatory sequence progressed, (2) by contrast, adhesiveness, springiness and cohesiveness regularly increased until the time of swallowing, (3) median particle size, indicating the bolus particle size distribution, decreased mostly during the first third of the masticatory sequence, (4) except for hardness, the rheological changes still appeared in the boluses collected just before swallowing, and (5) physical changes occurred, with sensory stickiness being described by the subjects as a dominant perception of the bolus at the end of mastication.

Conclusions

Although these physical and sensory changes progressed in the course of mastication, those observed just before swallowing seem to be involved in swallowing initiation. They can be considered as strong candidates for sensory inputs from the bolus that are probably crucially involved in the triggering of swallowing, since they appeared in boluses prepared in various mastication strategies by different subjects.

Videofluorographic evaluation of mastication and swallowing of Japanese udon noodles and white rice

A videofluorographic (VF) swallowing study was performed on 22 healthy volunteers to observe the complete mastication and swallowing phases for Japanese udon noodles and white rice. The hardness, stickiness, and cohesiveness of food samples were measured using a food texture analyzing system. VF images were acquired using a versatile fluoroscopic unit and barium sulfate was used as a contrast medium. Udon noodles had a harder and smoother food texture than white rice. Fewer chewing movements and more stage 2 transport were seen during the consumption of udon noodles than for white rice.

Sensory input pathways and mechanisms in swallowing: a review

Over the past 20 years, research on the physiology of swallowing has confirmed that the oropharyngeal swallowing process can be modulated, both volitionally and in response to different sensory stimuli. In this review we identify what is known regarding the sensory pathways and mechanisms that are now thought to influence swallowing motor control and evoke its response. By synthesizing the current state of research evidence and knowledge, we identify continuing gaps in our knowledge of these mechanisms and pose questions for future research.

Coordination of Mastication, Swallowing and Breathing

The pathways for air and food cross in the pharynx. In breathing, air may flow through either the nose or the mouth, it always flows through the pharynx. During swallowing, the pharynx changes from an airway to a food channel. The pharynx is isolated from the nasal cavity and lower airway by velopharyngeal and laryngeal closure during the pharyngeal swallow. During mastication, the food bolus accumulates in the pharynx prior to swallow initiation. The structures in the oral cavity, pharynx and larynx serve multiple functions in breathing, speaking, mastication and swallowing. Thus, the fine temporal coordination of feeding among breathing, mastication and swallowing is essential to provide proper food nutrition and to prevent pulmonary aspiration. This review paper will review the temporo-spatial coordination of the movements of oral, pharyngeal, and laryngeal structures during mastication and swallowing, and temporal coordination between breathing, mastication, and swallowing.

Dysphagia in stroke and neurologic disease

Dysphagia is a common problem in neurologic disease. The authors describe rates of dysphagia in selected neurologic diseases, and the evaluation and treatment of dysphagia in this population. Applicable physiology and aspects of neural control are reviewed. The decision-making process to determine oral feeding versus alternative means of alimentation is examined.

The neurobiology of swallowing and dysphagia

The neurobiological study of swallowing and its dysfunction, defined as dysphagia, has evolved over two centuries beginning with electrical stimulation applied directly to the central nervous system, and then followed by systematic investigations that have used lesioning, transmagnetic stimulation, magnetoencephalography, and functional magnetic resonance imaging. The field has evolved from mapping the central neural pathway and peripheral nerves, to defining the importance of specific regions of the lower brain stem in terms of interneurons that provide sequential control for multiple muscles in the most complex reflex elicited by the nervous system, the pharyngeal phase of swallowing. The field is now emerging into defining how the higher cortical regions interact with this brain stem control and is providing a broader perspective of how the intact nervous system functions to control the three phases of swallowing (i.e., oral, pharyngeal, and esophageal). Much of the present interest focuses on how to retrain a damaged nervous system using a variety of stimulus techniques, which follow fundamentals in rehabilitation of the nervous system.