Viscosity and Non-Newtonian Features of Thickened Fluids Used for Dysphagia Therapy

Paediatric Solid Oral Dosage Forms for Combination Products: Improving In Vitro Swallowability of Minitablets Using Binary Mixtures with Pellets

There is a growing interest in enhancing the acceptability of paediatric pharmaceutical formulations. Solid oral dosage forms (SODF) are being considered as an alternative to liquid formulations, but they may compromise palatability as large volumes may be required. We hypothesised that a binary mixture of paediatric SODF, designed to increase the formulation maximum packing fraction, could reduce the suspension viscosity and facilitate swallowing. Using the Paediatric Soft Robotic Tongue (PSRT) - an in vitro device inspired by the anatomy and physiology of 2-year-old children - we investigated the oral phase of swallowing for multi-particulate formulations, i.e., pellets (350 and 700 µm particles), minitablets (MTs, 1.8 mm), and their binary mixtures (BM), by evaluating oral swallowing time, the percentage of particles swallowed, and post-swallow residues. We also conducted a systematic analysis of the effect of feeding method, bolus volume, carrier type, particle size, and particle volume fraction on pellets swallowability. The results demonstrated that the introduction of pellets affected the flowing ability of the carriers, increasing shear viscosity. The size of the pellets did not appear to influence particle swallowability but raising the particle volume fraction (v.f.) above 10% resulted in a decrease in the percentage of particles swallowed. At v.f. 0.4, pellets were easier to swallow (+ 13.1%) than MTs, being the administration method used highly dependent on the characteristics of the multi-particulate formulation under consideration. Finally, mixing MTs with only 24% of pellets improved particle swallowability, achieving swallowing levels similar to those of pellets alone. Thus, combining SODF, i.e., MTs and pellets, improves MT swallowability, and offers new possibilities for adjusting product palatability, being particularly attractive for combination products.

Management of Children with Swallowing Problems: New Advances in Paediatric Thickeners

A satellite symposium on the evaluation and management of dysphagia in children was held during the 12th Annual Congress of the European Society for Swallowing Disorders (ESSD) in Leuven, Belgium, on 14th September 2022. Dysphagia is the impairment or difficulty in swallowing and may have an oropharyngeal or oesophageal cause. This can result in delayed transit of liquids or solid food from the mouth to the stomach. Food thickening agents can reduce regurgitation and improve swallowing mechanics, particularly in infants and young children. At this symposium, Karen van Hulst, Speech and Language Therapist and Clinical Epidemiologist at Radboud University Medical Center, Amalia’s Children’s Hospital, the Netherlands, introduced the topic of dysphagia and its complications, and the evaluation of dysphagia. She then discussed the use of thickening agents in children with dysphagia. Ben Hanson from the Department of Engineering, University College London, UK, introduced the International Dysphagia Diet Standardization Initiative (IDDSI). The IDDSI has developed a standardised and practical method of measuring the thickness of liquid and food that can be used when preparing foods at home or in the hospital, and may be applied commercially. Analou Sugar, Clinical Lead in Paediatric Speech and Language Therapy at Chelsea and Westminster Hospital Foundation Trust, London, UK, ended the symposium with a presentation of her recent clinical experience using a new thickener (ThickenUp® Junior, Nestlé Health Science, Vevey, Switzerland) in paediatric patients.

Patients with dysphagia: How to supply nutrition through non-tube feeding

OBJECTIVE

Dysphagia has become one of the important factors that cause malnutrition in the whole age group. At present, tube feeding is still the mainstream means to solve the problem of dysphagia. However, tube feeding has physical and mental harm to people, and the ways of non-tube feeding are relatively diversified. The significance of the thickening mechanism described in some articles to solve the problem of dysphagia is not clear.

SETTING AND PARTICIPANTS

All patients with dysphagia worldwide, including oropharyngeal dysphagia (OD) and non-oropharyngeal dysphagia.

METHODS

We searched the literature in Pubmed, Web of Science and Cochrane Library and initially browsed the titles and abstracts. We reviewed the full text of the articles that met our topic, and the language of the article was limited to English.

RESULTS

We found that food thickening to a certain degree (350-1,750 cP) can reduce the complications of choking, aspiration, reflux, and other complications in patients with dysphagia, and reduce the social disorder, anxiety, and other psychological problems caused by catheterization and surgery. Significantly, food science engineers should invite clinicians to intervene in the development of specialty foods from different perspectives such as clinical pathophysiology and fluid mechanics.

CONCLUSION AND IMPLICATIONS

It is necessary to develop special foods for patients with dysphagia, which requires scientists from different disciplines to work together.

Rheological Properties and Stability of Thickeners for Clinical Use

The adaptation of liquids for patients with dysphagia requires precision and individualization in the viscosities used. We describe the variations of viscosity in water at different concentrations and evolution over time of the three compositions of commercial thickeners that are on the market (starch, starch with gums, and gum). By increasing the concentration in water, the viscosity of gum-based thickeners increases linearly, but it did not reach pudding texture, whereas the viscosity of the starch-based thickeners (alone or mixed with gums) rapidly reaches very thick textures. We modeled the viscosity at different concentrations of the four thickeners using regression analysis (R2 > 0.9). We analyzed viscosity changes after 6 h of preparation. The viscosity of gum-based thickeners increased by a maximum of 6.5% after 6 h of preparation, while starch-based thickeners increased by up to 43%. These findings are important for correct handling and prescription. Gum-based thickeners have a predictable linear behavior with the formula we present, reaching nectar and honey-like textures with less quantity of thickener, and are stable over time. In contrast, starch thickeners have an exponential behavior which is difficult to handle, they reach pudding-like viscosity, and are not stable over time.

Psyllium (Plantago ovata Forsk) in frozen banana pulp: Influence on rheological, nutritional and sensory characteristics

A frozen banana pulp with functional properties was developed and characterized in this work. For this, 0 g, 3 g, 5 g and 7 g of psyllium in 100 g of banana pulp were added. The use of this fiber in industrialized products can contribute to the nutritional enrichment of the products and provide functional benefits already acknowledged, such as lowering LDL cholesterol, lowering blood glucose, increasing satiety and relieving constipation. According to the World Health Organization, vegetable consumption should be increased, as it reduces the risk of chronic diseases. The main purpose of this work was to incorporate psyllium in frozen banana pulp to develop a healthy product. The samples were evaluated through chemical analyses, rheological properties and sensory testing with Check-All-That-Apply questions (CATA). The addition of psyllium had a significant effect not only on the viscosity but also on the sensory and nutritional properties of the frozen banana pulp. This study indicated that the production of frozen banana pulp with psyllium is viable, as it has desirable nutritional and sensory characteristics which can contribute to the maintenance of health.

Combining Liquid Oral Drugs with Thickener: Compatibility and Changes in Viscosity

Older adults with oropharyngeal dysphagia (OD) are unable to swallow pills safely, so some of them use liquid-formulated drugs mixed with thickeners to ensure safety. The aim of this study was to analyze the physical compatibility of a group of drugs with a thickener formulated with modified starch (Thick & Easy®). A secondary goal was to evaluate the amount of thickener needed to obtain the thickness levels 2, 3, and 4 defined by IDDSI framework for each drug. For this purpose, the rheological properties of the mixtures obtained were determined. Samples of each drug were prepared and 7, 10, and 12 g of thickener were added. Physical compatibility of the mixtures was observed; the apparent viscosity of the samples was measured using a rotational viscometer, and the results obtained were compared with the reference drug-free sample. We analyzed 45 medicinal products (38 active substances). Three drugs (almagate, ibuprofen, and macrogol) were found to be physically incompatible with the thickener and should not be mixed. Viscosity measurements indicated that clarithromycin and plantago ovata increased the viscosity of the mixture and required lower amount to achieve the target textures (110 cP, 590 cP, and 2620 cP for 7 g, 10 g, and 12 g in drug-free samples, respectively), whereas another subset reduced viscosity and required more thickener. This proved very relevant for acetylcysteine, amoxicillin, calcifediol, ferrous gluconate, fosfomycin, lactitol, lactulose, mepifiline, paracetamol, rivastigmine, sertraline, and tramadol. Measurements were below 1750 cP. Awareness of how each drug behaves when combined with thickeners is essential to avoid potential complications in OD.

Simple Advanced Preparation Method for Improving the Thickness Stability of Powder Thickening Agents in Dysphagia Management

Texture modification of foods by using thickening agents is a routine practice for assessing and treating dysphagic patients. However, a powder-thickened fluid's viscosity might change over time, and little has been proposed to overcome this inconsistency. This study aimed to evaluate variations in the thickness of a fluid thickened with a common xanthan gum-based powder and to explore the feasibility of a simple advanced preparation method for thickened liquids to improve thickness stability. Thickened fluids with concentrations of 1.0 g/100 mL, 0.7 g/100 mL, and 0.5 g/100 mL were prepared from both freshly opened and previously opened thickening powders. Fluid thickness was measured every 10 min in a series of International Dysphagia Diet Standardization Initiative flow tests. A significant time-dependent decline in thickness was observed for all three concentrations in both groups, namely those prepared with freshly opened and previously opened thickening powders, and the shortest periods to achieve a stable viscosity after liquid preparation for the two groups were 80 and 70 min, respectively. On diluting the thickened liquids from the base liquid, which was prepared at a concentration of 1.0 g/100 mL and stored at room temperature for 90 min, no significant time-dependent thickness changes were observed over the following 60 min. The simple protocol of preparing the thickest "base" liquid in advance and then diluting it to the desired thickness resulted in a consistent liquid thickness, with the prepared liquids ready to be clinically applied and consumed, with high stability within 60 min.

Influence of thickening agents on rheological properties and sensory attributes of dysphagic diet

Dysphagia is the difficulty during the progression of the bolus from the mouth to the stomach. Modifying the texture of the food is a fundamental factor for safe swallowing in patients with dysphagia since inadequate consistency can result in complications. To personalize and develop diets for dysphagia, understanding, and controlling the rheological and sensory properties of thickeners is useful. This review examines the different types of thickeners used to modify the texture of foods, as well as their influence on rheological properties and sensory attributes to efficiently manage the diet in dysphagia. The study discusses characteristics such as: hardness, viscosity, viscoelasticity, as well as sensory attributes related to rheology. The thickeners xanthan gum, methylcellulose, carboxymethylcellulose, guar gum, linseed, and chia, carboxymethylated curdlan, and konjac glucomannan were reviewed in this work. Sensory evaluations of different foods have already been carried out on some products such as: meats, carrots, soups, pates, and timbales with their modified textures. The sensory attributes measured among hydrocolloids are strongly correlated with rheological parameters. Dysphagic diets should have less hardness and adherence, but with adequate cohesiveness to facilitate chewing, swallowing to protect from aspiration and reduction of residues in the oropharynx. The use of a single type of thickener may not be ideal, their mixtures and synergistic effect can improve the viscous and elastic characteristics of foods, to obtain safe food to swallow and to improve the sensory interest of dysphagic patients. Personalized recommendations with follow-up on swallowing approaches, respecting patient's individuality, explaining thickening agents' differences would be pertinent.

Effect of mixing method on resulting thickness of infant formula

Previous research shows that factors such as time, temperature, nutritional make-up of a liquid, and type of thickening agent can significantly alter the resulting thickness of liquids. This study sought to determine the effect of three distinct mixing methods on the resulting thickness of ready to feed infant formulas mixed to Mildly and Moderately Thick (International Dysphagia Diet Standardization Initiative [IDDSI] Levels 2 and 3) with three different thickening agents. Eight commercially available infant formulas were mixed with three different thickening agents by three different mixing methods. The IDDSI Syringe Flow Test was used to categorize the thickened formulas. Chi square analyses were completed to determine the impact of mixing method on the thickened formulas. The majority (94%) of thickened formula combinations prepared to a target Mildly Thick consistency produced thickened formula that was thinner or thicker than the target. In contrast, the majority (76%) of thickened formula combinations prepared to a target Moderately Thick (IDDSI Level 3) consistency produced thickened formula that was equivalent to the target consistency. A statistically significant relationship was found between mixing methods and resulting IDDSI category for samples mixed to a target of Moderately Thick. The thickening agent and method of mixing must be considered carefully when preparing infant formulas to Mildly and Moderately Thick target IDDSI categories. Based on results of this study, it is recommended that providers utilize a clinical testing method, such as the IDDSI Syringe Flow Test, when attempting to create a Mildly Thick formula consistency.

Formulation development of paracetamol instant jelly for pediatric use

OBJECTIVE

Paracetamol is a common antipyretic and analgesic medicine used in childhood illness by parents and physicians worldwide. Paracetamol has a bitter taste that is considered as a significant barrier for drug administration. This study aimed to develop an oral dosage form that is palatable and easy to swallow by pediatric patients as well as to overcome the shortcomings of liquid formulations.

METHODS

The paracetamol was encapsulated in beads, which were prepared mainly from alginate and chitosan through electrospray technique. The paracetamol beads were sprinkled on the instant jelly prepared from glycine, ι-carrageenan and calcium lactate gluconate. The paracetamol instant jelly characteristics, in terms of physical appearance, texture, rheology, in vitro drug release and palatability were assessed on a human volunteer.

RESULTS

The paracetamol instant jelly was easily reconstituted in 20 mL of water within 2 min to form jelly with acceptable consistency and texture. The jelly must be ingested within 30 min after reconstitution to avoid the bitter taste. The palatability assessment carried out on 12 human subjects established the similar palatability and texture of the paracetamol instant jelly dosage comparable to the commercial paracetamol suspension and was found to be even better in overcoming the aftertaste of paracetamol.

CONCLUSION

Such findings indicate that paracetamol instant jelly will compensate for the use of sweetening and flavoring agents as well as develop pediatric dosage forms with limited undesired excipients.

Evaluation of non-Newtonian Viscosities of Liquid Foods in Swallowing Process Using Inclined Flow Channel Instrument

To evaluate the non-Newtonian viscosities of liquid foods thickened for assistance of swallowing in nursing-care practice, an inclined flow channel instrument was investigated for development into a structurally simple and easy-to-use viscometer. Experimental analysis of the flows of Newtonian and non-Newtonian test liquids in the instrument derived a dimensionless relation expressing changes of the friction coefficient in the flow process which was indicated by the relative flow length, considering the shear rate level in the swallowing process. A methodology to evaluate uniquely the viscosities of liquid foods undergoing the swallowing process was presented using the measurements such as the flow length and velocity in the instrument.

Experimental and Computational Investigation of the IDDSI Flow Test of Liquids Used in Dysphagia Management

The International Dysphagia Diet Standardisation Initiative (IDDSI) flow test, using a standard 10-mL syringe, is being adopted in many countries for clinical measurement of the consistency of drinks. The working hypothesis is that thickening drinks to retard flow can be advantageous for individuals who struggle to cope with thin drinks. This study assesses how the IDDSI test relates to rheology and clinical knowledge of physiological flows during swallowing. With no pre-existing analytical solution for internal flow through the syringe, a computational model was designed, incorporating rheometry data from a variety of Newtonian and non-Newtonian liquids. The computational model was validated experimentally across the range of liquids but the technique showed limitations in simulating dripping and cohesiveness. Gum-based liquids which were strongly shear-thinning (0.12 < n < 0.25) showed plug-flow characteristics with 90% of the shear occurring in only 22% of the radial dimension. Shear rates were maximal at the nozzle outlet (> 60 times higher than the barrel) and reached 7400/s for the thinnest gum-based liquid. Shear rheology data alone was unable to describe the flow of these drinks. The flow conditions in the test varied according to the type and consistency of liquid, relating to the desired clinical effect.

The impact of modification techniques on the rheological properties of dysphagia foods and liquids

Modifying food and the textures of food has been done for decades within the food science and technology field. More recently, modifying the texture of foods has been used to manage swallowing disabilities (dysphagia). Swallowing disabilities are often associated with dehydration and malnutrition, thus nutritional intervention has formed part of serving texture-modified diets. The question remains whether these modification techniques are viable for individuals with swallowing disabilities living in majority world countries. This study used two modification methods on a widely used specialized nutritious food (SNF) to determine whether it may be modified and used in dysphagia management. The techniques had to be ergonomic and economically appropriate for individuals with swallowing disabilities living in majority world countries. The International Dysphagia Diet Standardization Initiative's (IDDSI) standards were used to determine whether the texturally modified SNF is safe for swallowing. Rheological measurements were performed to determine apparent viscosity and structure recovery of each sample. The effects of two modification techniques, aeration and particle separation, on the rheological properties of the SNF were also measured and analyzed. It was determined that both milk and water could be used with this SNF to create a dysphagia diet, but only under certain conditions. The overall results indicated that heating the samples increased the apparent viscosity and exacerbated lumping. Room temperature samples had less lumps and could be classified to the desired levels of the IDDSI (Level 2 and Level 4). Using a whisk to aerate the samples reduced lumps significantly and using a sieve to separate particles of liquid samples eliminated lumps. This study provides new data on how texture modification techniques and the IDDSI framework could be adapted to individuals living in majority world countries. By using modification techniques that are ergonomic and economically viable and an SNF with longevity, this study could be useful in guiding future training of nursing staff and caregivers of individuals living in poverty or resource-constrained communities. This study also adds to the data on the rheological properties of dysphagia foods, although this study did not make use of commercial thickeners generally used in the modification of diets.

Modulation of Tongue Pressure According to Liquid Flow Properties in Healthy Swallowing

Purpose During swallowing, the tongue generates the primary propulsive forces that transport material through the oral cavity toward the pharynx. Previous literature suggests that higher tongue pressure amplitudes are generated for extremely thick liquids compared with thin liquids. The purpose of this study was to collect detailed information about the modulation of tongue pressure amplitude and timing across the range from thin to moderately thick liquids. Method Tongue pressure patterns were measured in 38 healthy adults (aged under 60 years) during swallowing with 4 levels of progressively thicker liquid consistency (International Dysphagia Diet Standardisation Initiative, Levels 0 = thin, 1 = slightly thick, 2 = mildly thick, and 3 = moderately thick). Stimuli with matching gravity flow (measured using the International Dysphagia Diet Standardisation Initiative Flow Test; Cichero et al., 2017 ; Hanson, 2016 ) were prepared both with/without barium (20% weight per volume concentration) and thickened with starch and xanthan gum thickeners. Results After controlling for variations in sip volume, thicker liquids were found to elicit significantly higher amplitudes of peak tongue pressure and a pattern of higher (i.e., steeper) pressure rise and decay slopes (change in pressure per unit time). Explorations across stimuli with similar flow but prepared with different thickeners and with/without barium revealed very few differences in tongue pressure, with the exception of significantly higher pressure amplitudes and rise slopes for nonbarium, starch-thickened slightly and mildly thick liquids. Conclusions There was no evidence that the addition of barium led to systematic differences in tongue pressure parameters across liquids with closely matched gravity flow. Additionally, no significant differences in tongue pressure parameters were found across thickening agents. Supplemental Material https://doi.org/10.23641/asha.7616537.

Increased levels of substance P in patients taking beta-blockers are linked with a protective effect on oropharyngeal dysphagia

BACKGROUND

We have recently found a potential protective effect of beta-blockers on oropharyngeal dysphagia (OD). The action mechanism by which beta-blockers could wield this protective effect is unknown, but the neurotransmitter substance P (SP) could play a key role. The aim of this study was to analyze serum and saliva SP levels in patients taking beta-blockers (TBB), and to explore its relationship with OD.

METHODS

Adult (>50 year) patients TBB were randomly recruited from the primary care setting and 1:1 matched by age, sex, and Barthel Index (BI) with patients not taking beta-blockers (NTBB). Serum and saliva samples were taken and analyzed for their SP levels using an enzyme-linked immunosorbent assay (ELISA). Socio-demographic and clinical variables were collected. Dysphagia was evaluated in all patients using the clinical volume-viscosity swallow test (V-VST).

KEY RESULTS

We studied 28 patients TBB (64.96 ± 7.31 years, 57.1% women, BI 99.6 ± 1.31, carvedilol-equivalent dose 24.11 ± 18.12 mg) and 28 patients NTBB (65.61 ± 6.43 years, 57.1% women, BI 99.6 ± 1.31). SP serum levels were significantly higher in patients TBB (260.68 ± 144.27 vs 175.46 ± 108.36 pg/mL, P = .009) as were SP saliva levels (170.34 ± 146.48 vs 102.73 ± 52.28 pg/mL, P < .001) compared with patients NTBB. The prevalence of OD was 32.1% in patients TBB and 67.9% in patients NTBB (P = .015). Moreover, patients with OD had significantly lower SP saliva levels in comparison with patients without clinical signs of OD (98.39 ± 43.25 vs 174.69 ± 147.21 pg/mL) P < .001.

CONCLUSIONS & INFERENCES

We have found that serum and saliva SP levels are greater in patients TBB. This increase in SP levels could be the action mechanism by which beta-blockers protect patients from OD.

The effect of administration media on palatability and ease of swallowing of multiparticulate formulations

Multiparticulate formulations based on pellets, granules or beads, could be advantageous for paediatrics, geriatrics and patients with swallowing difficulties. However, these formulations may require suitable administration media to facilitate administration. The aim of this work was to investigate the effect of administration media properties on palatability and ease of swallowing of multiparticulates. A range of vehicles were developed using xanthan gum (XG) and carboxymethyl cellulose (CMC) as model hydrocolloids. Such vehicles were prepared at three consistency levels (Level 1 - 'syrup', Level 2 - 'custard' and Level 3 - 'pudding') to investigate the effect of viscosity on their performance as administration media. A randomised, single-blind sensory evaluation study was carried out in thirty healthy adult volunteers using microcrystalline cellulose pellets as model multiparticulates, dispersed in the hydrogels (and water as control) at a concentration of 250 mg in 5 ml. Samples were evaluated using 5-point scales. The use of hydrogels as administration media improved a range of sample attributes compared to water formulations, including appearance, taste, mouthfeel, ease of swallowing and residue in the mouth (all improved by ca. 0,5 points) and oral grittiness perception (improved by ca. 1 point). Polymeric hydrogels thickened to medium consistency (Level 2, XG 0.5% and CMC 1.0% w/v) demonstrated the best performance.

Development of International Terminology and Definitions for Texture-Modified Foods and Thickened Fluids Used in Dysphagia Management: The IDDSI Framework

Dysphagia is estimated to affect ~8% of the world's population (~590 million people). Texture-modified foods and thickened drinks are commonly used to reduce the risks of choking and aspiration. The International Dysphagia Diet Standardisation Initiative (IDDSI) was founded with the goal of developing globally standardized terminology and definitions for texture-modified foods and liquids applicable to individuals with dysphagia of all ages, in all care settings, and all cultures. A multi-professional volunteer committee developed a dysphagia diet framework through systematic review and stakeholder consultation. First, a survey of existing national terminologies and current practice was conducted, receiving 2050 responses from 33 countries. Respondents included individuals with dysphagia; their caregivers; organizations supporting individuals with dysphagia; healthcare professionals; food service providers; researchers; and industry. The results revealed common use of 3-4 levels of food texture (54 different names) and ≥3 levels of liquid thickness (27 different names). Substantial support was expressed for international standardization. Next, a systematic review regarding the impact of food texture and liquid consistency on swallowing was completed. A meeting was then convened to review data from previous phases, and develop a draft framework. A further international stakeholder survey sought feedback to guide framework refinement; 3190 responses were received from 57 countries. The IDDSI Framework (released in November, 2015) involves a continuum of 8 levels (0-7) identified by numbers, text labels, color codes, definitions, and measurement methods. The IDDSI Framework is recommended for implementation throughout the world.

Nutritional Aspects of Dysphagia Management

This chapter describes the nutritional aspects of dysphagia management by starting with the definition of these two conditions (dysphagia and malnutrition) that share three main clinical characteristics: (a) their prevalence is very high, (b) they can lead to severe complications, and (c) they are frequently underrecognized and neglected conditions. From an anatomical standpoint, dysphagia can result from oropharyngeal and/or esophageal causes; from a pathophysiological perspective, dysphagia can be caused by organic or structural diseases (either benign or malignant) or diseases causing impaired physiology (mainly motility and/or perception disorders). This chapter gathers up-to-date information on the screening and diagnosis of oropharyngeal dysphagia, the consequences of dysphagia (aspiration pneumonia, malnutrition, and dehydration), and on the nutritional management of dysphagic patients. Concerning this last topic, this chapter reviews the rheological aspects of swallowing and dysphagia (including shear and elongational flows) and its influence on the characteristics of the enteral nutrition for dysphagia management (solid/semisolid foods and thickened liquids; ready-to-use oral nutritional supplements and thickening powders), with special focus on the real characteristics of the bolus after mixing with human saliva.

"A Day in the Life of the Fluid Bolus": An Introduction to Fluid Mechanics of the Oropharyngeal Phase of Swallowing with Particular Focus on Dysphagia

By following the path of a liquid bolus, from the oral preparatory phase to the esophagus, we show that a few fundamental concepts of fluid mechanics can be used to better understand and assess the importance of bolus viscosity during human swallowing, especially when considering dysfunctional swallowing (dysphagia) and how it can be mitigated. In particular, we highlight the important distinction between different flow regimes (i.e. viscosity controlled versus. inertia controlled flow). We also illustrate the difference between understanding bolus movements controlled by a constant force (or pressure) and those controlled by a constant displacement (or velocity). We limit our discussion to simple, Newtonian liquids where the viscosity does not depend on the speed of flow. Consideration of non-Newtonian effects (such as shear thinning or viscoelasticity), which we believe play an important part in human swallowing, requires a sound grasp of the fundamentals discussed here and warrants further consideration in its own right.

Fork test: A new simple and reliable consistency measurement for the dysphagia diet

The objective of this study was to validate fork test which is a simple tool to assess the consistency of food. The consistencies of 27 water and thickener mixtures were measured with a viscometer. These measures were then compared to those obtained with fork test to evaluate the validity of fork test. The inter-observer and intra-observer reliabilities of the fork test were assessed with an intra-class correlation coefficient. The viscometer was used to obtain reference values for three categories (0-300 cP, 300-10,000 cP, and >10,000 cP) in order to categorize water and thickener mixtures into grade 1, grade 2, or grade 3 according to the results of fork test. Our results revealed that the fork test showed excellent validity (r = -0.889, p < 0.05), intra-observer reliability, and inter-observer reliability. Therefore, fork test may be used as a practical tool to assess food consistency.

Effect of pH on Rheological Properties of Dysphagia-Oriented Thickened Water

Flow and dynamic rheological properties of thickened waters prepared with commercial food thickeners were investigated at different pH levels (3, 4, 5, 6, and 7). The commercial xanthan gum (XG)-based thickener (thickener A) and starch-based thickener (thickener B), which have been commonly used in a domestic hospital and nursing home for patients with swallowing difficulty (dysphagia) in Korea, were selected in this study. Thickened samples with both thickeners at different pH levels showed high shear-thinning flow behaviors (n=0.08~0.22). Thickened samples at pH 3 showed higher n values and lower consistency index (K) values when compared to those at other pH levels. The K values of thickener A increased with an increase in pH level, while the n values decreased, showing that the flow properties greatly depended on pH. There were no noticeable changes in the K values of thickener B between pH 4 and 7. At pH 3, the thickened water with thickener A showed a higher storage modulus (G′) value, while that with thickener B showed a lower G′. These rheological parameters exhibited differences in rheological behaviors between XG-based and starch-based thickeners, indicating that the rheological properties of thickened waters appear to be greatly influenced by the acidic condition and the type of food thickener. Appropriately selecting a commercial food thickener seems to be greatly important for the preparation of thickened acidic fluids with desirable rheological properties for safe swallowing.

Implications of changing the amount of thickener in thickened infant formula for infants with dysphagia

When a dysphagic infant is prescribed thickened infant formula (TIF) as a treatment method, some clinicians determine their own addition rates of thickener to meet the specific needs of the infant rather than relying on the directions on the tin. In this study the rheological behaviour of a TIF at different addition levels of thickener was measured to determine whether there was a difference in full rheological response and in viscosity. In addition, the time taken for the TIF to reach a near-stable viscosity was also measured. One hundred grams of Karicare® infant formula was made up according to the manufacturer’s instructions and Karicare® feed thickener was added at levels of 2, 3, 4, 5, and 6 g, respectively. A strain-controlled rheometer (ARES) with Couette geometry was used to rheologically characterise the TIF at the different levels of thickener addition. There was a significant difference in viscosity between the low levels and the higher levels of addition thickener (p < 0.05). Also, the low levels of thickener addition showed Newtonian-like behaviour, whereas the higher levels of addition were shear-thinning. The time taken for the thickener to reach a near-stable viscosity was found to be 10 min. Guidelines for thickened infant formula need to take into account the different levels of thickener addition rates.

A statistical analysis of cervical auscultation signals from adults with unsafe airway protection

Background

Aspiration, where food or liquid is allowed to enter the larynx during a swallow, is recognized as the most clinically salient feature of oropharyngeal dysphagia. This event can lead to short-term harm via airway obstruction or more long-term effects such as pneumonia. In order to non-invasively identify this event using high resolution cervical auscultation there is a need to characterize cervical auscultation signals from subjects with dysphagia who aspirate.

Methods

In this study, we collected swallowing sound and vibration data from 76 adults (50 men, 26 women, mean age 62) who underwent a routine videofluoroscopy swallowing examination. The analysis was limited to swallows of liquid with either thin (<5 cps) or viscous (≈300 cps) consistency and was divided into those with deep laryngeal penetration or aspiration (unsafe airway protection), and those with either shallow or no laryngeal penetration (safe airway protection), using a standardized scale. After calculating a selection of time, frequency, and time-frequency features for each swallow, the safe and unsafe categories were compared using Wilcoxon rank-sum statistical tests.

Results

Our analysis found that few of our chosen features varied in magnitude between safe and unsafe swallows with thin swallows demonstrating no statistical variation. We also supported our past findings with regard to the effects of sex and the presence or absence of stroke on cervical ausculation signals, but noticed certain discrepancies with regards to bolus viscosity.

Conclusions

Overall, our results support the necessity of using multiple statistical features concurrently to identify laryngeal penetration of swallowed boluses in future work with high resolution cervical auscultation.

Relationships Among Rheological, Sensory Texture, and Swallowing Pressure Measurements of Hydrocolloid-Thickened Fluids

The objective of this study was to examine the relationships among three categories of measurements (rheological, sensory texture, and swallowing pressure) from fluids thickened to two different viscosities with 15 different hydrocolloids. Fluids at viscosities of 300 and 1500 cP (at 30 s(-1)) were targeted because these are the viscosities corresponding to the barium standards used in radiographic dysphagia diagnosis. Within the low viscosity (nectar) fluids (300 cP), the sensory properties thickness, stickiness, adhesiveness, mouth coating, and number of swallows were highly positively correlated with each other and highly positively correlated with the flow behavior index, n value (an indicator of shear-thinning behavior). Within the higher viscosity (thin honey) fluids (1500 cP), the sensory textures of adhesiveness, stickiness, mouth coating, and number of swallows correlated positively with rheological measures of n value. Swallowing pressures measured in the anterior oral cavity correlated negatively with the consistency coefficient k [shear stress/(shear rate) (n) ]. Samples that were more shear thinning (lower n values, higher k values) were generally perceived as less thick, with less adhesive properties (stickiness, adhesiveness, mouthcoating, and number of swallows). This information can be useful for selecting thickeners for people with dysphagia. A desirable thickener for many dysphagic patients would be one that allowed for a safe swallow by being viscous enough to reduce airway penetration, yet pleasant to drink, having the minimal perceived thickness and mouthcoating associated with greater shear thinning.

Viscosity of dysphagia-oriented cold-thickened beverages: effect of setting time at refrigeration temperature

BACKGROUND

Although extensive literature is available on the viscosity of thickened beverages with food thickeners, no attempt has been made to study the effect of setting time on the viscosity of pudding-like cold-thickened beverages with xanthan gum (XG)-based thickeners by using a rheometer. In particular, it is of considerable practical importance to investigate the effect of setting time on their viscosity at 5°C because some cold-thickened beverages will be prepared in the kitchen in bulk and stored at 5°C before serving or consuming rather than serving immediately upon mixing with thickeners.

AIMS

To examine the effect of different setting times (15-120 min) on the viscosity of cold-thickened beverages prepared with various XG-based food thickeners, and also to compare the viscosity differences among the various cold beverages and XG-based food thickeners in beverage-thickener mixture systems.

METHODS & PROCEDURES

Four commercially available XG-based food thickeners (A-D) and three cold beverages (water, orange juice and milk) were used for the preparation of cold-thickened beverages. The thickened sample was portioned into six samples for the designated setting times and then stored at 5°C over setting time. Their apparent viscosity (η(a,50)) at 50 s(-1) was measured using a rheometer.

OUTCOMES & RESULTS

The largest increases in η(a,50) values for thickened beverages, except for water, were observed at 15 min (p < 0.05), showing a pudding-like fluid, and at longer time periods their η(a,50) values gradually increased or were constant with an increase in setting time. The percentage increase in viscosity values at different setting times (15-120 min) as compared with the control (0 min) was less pronounced in the thickened orange juice and milk samples with thickener A over setting time, indicating that the thickened beverages with thickener A had more stable structure compared with those with other thickeners (B-D) over time. Statistical analysis showed that changes in the viscosity of cold-thickened beverages over setting time are greatly influenced by the type of beverages and thickeners.

CONCLUSIONS & IMPLICATIONS

Cold-thickened beverages should be carefully prepared with instant commercial XG-based food thickeners because they produced different thickening patterns over setting time which clinicians must consider for a safe and easy swallowing. The information presented in this study will provide both clinicians and patients with additional knowledge to prepare cold-thickened beverages with the corrected viscosity for safe swallowing.

The influence of food texture and liquid consistency modification on swallowing physiology and function: a systematic review

Texture modification has become one of the most common forms of intervention for dysphagia, and is widely considered important for promoting safe and efficient swallowing. However, to date, there is no single convention with respect to the terminology used to describe levels of liquid thickening or food texture modification for clinical use. As a first step toward building a common taxonomy, a systematic review was undertaken to identify empirical evidence describing the impact of liquid consistency and food texture on swallowing behavior. A multi-engine search yielded 10,147 non-duplicate articles, which were screened for relevance. A team of ten international researchers collaborated to conduct full-text reviews for 488 of these articles, which met the study inclusion criteria. Of these, 36 articles were found to contain specific information comparing oral processing or swallowing behaviors for at least two liquid consistencies or food textures. Qualitative synthesis revealed two key trends with respect to the impact of thickening liquids on swallowing: thicker liquids reduce the risk of penetration-aspiration, but also increase the risk of post-swallow residue in the pharynx. The literature was insufficient to support the delineation of specific viscosity boundaries or other quantifiable material properties related to these clinical outcomes. With respect to food texture, the literature pointed to properties of hardness, cohesiveness, and slipperiness as being relevant both for physiological behaviors and bolus flow patterns. The literature suggests a need to classify food and fluid behavior in the context of the physiological processes involved in oral transport and flow initiation.

Variations in tongue-palate swallowing pressures when swallowing xanthan gum-thickened liquids

Thickened liquids are frequently recommended to reduce the risk of aspiration in patients with oropharyngeal dysphagia. Although it has previously been reported that tongue-palate pressures increase when swallowing spoon-thick and semi-solid consistencies compared to thin liquids, relatively little is known about how swallowing behaviors differ when swallowing liquids of nectar- or honey-thick consistency. Furthermore, previous studies have primarily used starch-based thickeners, and little is known about swallowing behaviors with xanthan gum-thickened liquids, which have recently been introduced for dysphagia management. In this study, we measured variations in tongue-palate pressures during the swallowing of liquids thickened to apparent viscosities of 190, 250, and 380 mPa s at 50/s using increasing concentrations of xanthan gum (0.5, 0.63 and 0.87 w/w%). The viscosity differences between these nectar- and honey-thick stimuli were confirmed to exceed sensory perceptual discrimination thresholds. Data were collected from 78 healthy adults in two sex-balanced age-groups (young; mature) and compared to reference values obtained during water swallowing. The results confirm that increased amplitudes of tongue-palate pressure were used when swallowing the thickened liquid stimuli, compared to swallows of water, and for the honey-thick liquid compared to the two nectar-thick liquids. Age-related reductions were seen in tongue strength but not in swallowing pressures, which fell below 40 % of maximum isometric pressure values. Thus, the use of xanthan gum-thickened liquids is unlikely to tax the swallowing system in terms of tongue pressure generation requirements, even in seniors with reduced maximum isometric tongue pressure measures.

Oral perceptual discrimination of viscosity differences for non-newtonian liquids in the nectar- and honey-thick ranges

Thickened liquids are frequently used in the management of oropharyngeal dysphagia. Previous studies suggest that compression of a liquid bolus between the tongue and the palate in the oral phase of swallowing serves a sensory function, enabling the tuning of motor behavior to match the viscosity of the bolus. However, the field lacks information regarding healthy oral sensory discrimination ability for small differences in liquid viscosity. We undertook to measure oral viscosity discrimination ability for five non-Newtonian xanthan gum-thickened liquids in the nectar- and honey-thick range. Xanthan gum concentration ranged from 0.5 to 0.87 % and increased by an average of 0.1 % between stimuli in the array. This translated to an average apparent viscosity increase of 0.2-fold between adjacent stimuli at 50 reciprocal seconds (/s). A triangle test paradigm was used to study stimulus discrimination in 78 healthy adults in two, sex-balanced age cohorts. Participants were provided 5-ml samples of liquids in sets of three; one liquid differed in xanthan gum concentration from the other two. Participants were required to sample the liquid orally and indicate which sample was perceived to have a different viscosity. A protocol of 20 sets (60 samples) allowed calculation of the minimum difference in xanthan gum concentration detected accurately. On average, participants were able to accurately detect a 0.38-fold increase in xanthan-gum concentration, translating to a 0.67-fold increase in apparent viscosity at 50/s. The data did not suggest the existence of a nonlinear point boundary in apparent viscosity within the range tested. No differences in viscosity discrimination were found between age cohorts or as a function of sex. The data suggest that for xanthan gum-thickened liquids, there may be several increments of detectably different viscosity within the ranges currently proposed for nectar- and honey-thick liquids. If physiological or functional differences in swallowing can be demonstrated for these smaller increments of detectably different viscosity, more narrowly defined categories of thickened liquids for dysphagia management will be warranted.

Comparison of different gum-based thickeners using a viscometer and line spread test: a preliminary study

Objective

To compare fluid thickeners composed of starch polysaccharide (STA), guar gum-based polysaccharide (GUA), and xanthan gum-based polysaccharide (XAN) with the use of a viscometer and a line spread test (LST) under various measurement conditions.

Methods

The viscosity of thickened fluid with various concentrations (range, GUA 1%-4%, XAN 1%-6%, STA 1%-7%, at intervals of 1%) was measured with a rotational viscometer with various shear rates (1.29 s^-1, 5.16 s^-1, 51.6 s^-1, and 103 s^-1) at a temperature of 35℃, representing body temperature. The viscosity of STA showed time dependent alteration. So STA was excluded. Viscosities of GUA and XAN (range of concentration, GUA 1%-3%, XAN 1%-6%, at intervals of 1%) were measured at a room temperature of 20℃. LST was conducted to compare GUA and XAN (concentration, 1.5%, 2.0%, and 3.0%) at temperatures of 20℃ and 35℃.

Results

The viscosities of 1% GUA and XAN were similar. However, viscosity differences between GUA and XAN were gradually larger as concentration increased. The shear thinning effect, the inverse relationship between the viscosity and the shear rate, was more predominant in XAN than in GUA. The results of LST were not substantially different from GUA and XAN, in spite of the difference in viscosity. However manufacturers' instructions do not demonstrate the rheological properties of thickeners.

Conclusion

The viscosities of thickened fluid were different when the measurement conditions changed. Any single measurement might not be sufficient to determine comparable viscosity with different thickeners. Clinical decision for the use of a specific thickener seems to necessitate cautious consideration of results from a viscometer, LST, and an expert's opinion.

Matching the rheological properties of videofluoroscopic contrast agents and thickened liquid prescriptions

In the treatment of oropharyngeal dysphagia, the link between diagnosis and prescription of thickened liquids that are safe to swallow is not always straightforward. Frequently, the capacity to objectively assess and quantify the rheological properties of diagnostic test fluids and to select "rheologically equivalent" dietary products is missing. Perhaps sometimes the importance of an objective comparison is not fully appreciated because two liquids seem reasonably similar in a subjective comparison (e.g., flow from a spoon). The present study deals with some of these issues. Shear viscosity measurements were used to characterize the flow behavior of videofluoroscopic contrast agents and of thickened fluids prepared with commercial thickening agents. Effects of time and composition of the different fluids were analyzed regarding shear-rate-dependent viscosity. Nearly all materials tested showed a pronounced dependence of viscosity with shear rate ("shear thinning"). Results confirm that it is feasible (but not always straightforward) to "match" the viscosities of diagnostic fluids and thickened beverages if certain precautions are taken. For example, the time required to reach final viscosity levels can be significant for some thickeners, particularly when used with liquids containing contrast agents. It is recommend to use only diagnostic materials and thickening agents for which reliable viscosity data are available.