Julie A.Y. Cichero

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.

Acoustic signature of the normal swallow: characterization by age, gender, and bolus volume.

Despite growing clinical use, cervical auscultation suffers from a lack of research-based data. One of the strongest criticisms of cervical auscultation is that there has been little research to demonstrate how dysphagic swallowing sounds are different from normal swallowing sounds. In order to answer this question, however, one first needs to document the acoustic characteristics of “normal,” nondysphagic swallowing sounds. This article provides the first normative database of normal swallowing sounds for the adult population. The current investigation documents the acoustic characteristics of normal swallowing sounds for individuals from 18 to more than 60 years of age over a range of thin liquid volumes. Previous research has shown the normal swallow to be a dynamic event. The normal swallow is sensitive to aging of the oropharyngeal system, and also to the volume of bolus swallowed. The current investigation found that the acoustic signals generated during swallowing were sensitive to an individuals age and to the volume of the bolus swallowed. There were also some gender-specific differences in the acoustic profile of the swallowing sound. It is anticipated that the results will provide a catalyst for further research into cervical auscultation.

How Thick Is Thick? Multicenter Study of the Rheological and Material Property Characteristics of Mealtime Fluids and Videofluoroscopy Fluids

Abstract Objective rheological assessment of fluids given to dysphagic patients at mealtime and during videofluoroscopy was carried out using a multicenter format. Thin, quarter-thick, half-thick and full-thick fluids were examined for the degree of correlation between mealtime fluids and their allegedly matched videofluoroscopy counterparts. The study was carried out to determine whether perceived subjective differences between mealtime fluids and videofluoroscopy fluids could be quantified using the rheological parameters of viscosity, density, and yield stress. The results showed poor correlation between mealtime fluids and videofluoroscopy fluids over all parameters. In general, the videofluoroscopy fluids were more viscous, more dense, and showed higher yield stress values than their mealtime counterparts. Given these results, it is reasonable to assume that the fluids used during videofluoroscopy do not provide an accurate indication of swallowing ability at mealtime. Therefore, it is suggested that clinicians use objective methods to rheologically match videofluoroscopy fluids to mealtime fluids.

Detection of Swallowing Sounds: Methodology Revisited

Cervical auscultation is in the process of gaining clinical credibility. In order for it to be accepted by the clinical community, the procedure and equipment used must first be standardized. Takahashi et al. [Dysphagia 9:54-62, 1994] attempted to provide benchmark methodology for administering cervical auscultation. They provided information about the acoustic detector unit best suited to picking up swallowing sounds and the best cervical site to place it. The current investigation provides contrasting results to Takahashi et al. with respect to the best type of acoustic detector unit to use for detecting swallowing sounds. Our study advocates an electret microphone as opposed to an accelerometer for recording swallowing sounds. However, we agree on the optimal placement site. We conclude that cervical auscultation is within reach of the average dysphagia clinic.

The physiologic cause of swallowing sounds: Answers from heart sounds and vocal tract acoustics

Abstract. A hypothetical discussion of the cause of swallowing sounds is presented. It is suggested that the pharynx contains a number of valves and pumps that produce reverberations within the pharynx to generate swallowing sounds. As heart sounds are propagated via vibration of muscles and valves, it is further suggested that an analogy exists between the generation of heart sounds and swallowing sounds. This new theory is known as the cardiac analogy hypothesis. The inability of the current literature to explain the cause of swallowing sounds is seen to limit the diagnostic potential of cervical auscultation for dysphagia assessment. Future investigators are encouraged to prove or disprove the cardiac analogy hypothesis.

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.

Thickened Fluids and Water Absorption in Rats and Humans

Individuals with dysphagia are commonly provided with oral fluids thickened to prevent aspiration. Most thickening agents are either gum-based (guar or xanthan) or are derived from modified starches. There is evidence, predominantly anecdotal, that dysphagic individuals are subclinically dehydrated. Dysphagia has a particular impact on elderly individuals and there is justifiable concern for dehydration in this population. It has been speculated that dehydration may, in part, be the result of the water-holding capacity of these thickening agents decreasing water absorption from the gut. The aim of this study was to determine the rate of intestinal absorption of water from thickened fluids. The method used was a laboratory tracer study in rats and humans in vivo. We found that there were no significant differences in water absorption rates between thickened fluids or pure water irrespective of thickener type (modified maize starch, guar gum, or xanthan gum). These data provide no support for the view that the addition of thickening agents, irrespective of type, to orally ingested fluids significantly alters the absorption rate of water from the gut.

Physiological Factors Related to Aspiration Risk: A Systematic Review

Penetration–aspiration is considered the most serious component of oropharyngeal dysphagia. Clinicians regularly evaluate the pathophysiology of swallowing and postulate reasons or mechanisms behind penetration–aspiration. In this article we share the results of a two-stage literature review designed to elucidate the association between abnormalities in physiological measures of swallowing function and the occurrence of penetration–aspiration. In the first stage, a broad scoping review was undertaken using search terms for nine different structures involved in oropharyngeal swallowing. In the second stage, based on the results of the initial search, a more focused systematic review was undertaken which explored the association between aspiration and abnormalities in respiratory, tongue, hyoid, and laryngeal function in swallowing. A total of 37 articles underwent detailed quality review and data extraction in the systematic review. The results support measurement of tongue strength, anatomically normalized measures of hyoid movement, bolus dwell time in the pharynx while the larynx remains open, respiratory rate, and respiratory swallow phasing as parameters relevant to aspiration risk.

Crushed Tablets: Does the Administration of Food Vehicles and Thickened Fluids to Aid Medication Swallowing Alter Drug Release?

PURPOSE To evaluate the influence of co-administered vehicles on in vitro dissolution in simulated gastric fluid of crushed immediate release tablets as an indicator for potential drug bioavailability compromise. METHODS Release and dissolution of crushed amlodipine, atenolol, carbamazepine and warfarin tablets were tested with six foods and drinks that are frequently used in the clinical setting as mixers for crushed medications (water, orange juice, honey, yoghurt, strawberry jam and water thickened with Easythick powder) in comparison to whole tablets. Five commercial thickening agents (Easythick Advanced, Janbak F, Karicare, Nutilis, Viscaid) at three thickness levels were tested for their effect on the dissolution of crushed atenolol tablets. RESULTS Atenolol dissolution was unaffected by mixing crushed tablets with thin fluids or food mixers in comparison to whole tablets or crushed tablets in water, but amlodipine was delayed by mixing with jam. Mixing crushed warfarin and carbamazepine tablets with honey, jam or yoghurt caused them to resemble the slow dissolution of whole tablets rather than the faster dissolution of crushed tablets in water or orange juice. Crushing and mixing any of the four medications with thickened water caused a significant delay in dissolution. When tested with atenolol, all types of thickening agents at the greatest thickness significantly restricted dissolution, and products that are primarily based on xanthan gum also delayed dissolution at the intermediate thickness level. CONCLUSIONS Dissolution testing, while simplistic, is a widely used and accepted method for comparing drug release from different formulations as an indicator for in vivo bioavailability. Thickened fluids have the potential to retard drug dissolution when used at the thickest levels. These findings highlight potential clinical implications of the addition of these agents to medications for the purpose of dose delivery and indicate that further investigation of thickened fluids and their potential to influence therapeutic outcomes is warranted.

Liquid barium is not representative of infant formula: characterisation of rheological and material properties

Infants experiencing dysphagia may undergo a videofluoroscopic swallow study (VFSS) to assess radiologically their coordination for sucking, swallowing, and breathing. No studies known to these authors have investigated whether the liquids used during infant radiological procedures are representative of liquids routinely fed to infants (e.g., formula). This study used an Advanced Rheometric Expansion System (ARES) strain-controlled rheometer to compare prethickened antiregurgitation formula, regular (thin) infant formula, and two types of regular infant formula, hand-thickened with a thickening agent and with liquid Polibar™ (barium-impregnated liquid). The viscosity, density, and yield stress of all samples were determined. Heated versus cooled liquids were compared. Results showed a significant difference in all rheological and material property parameters among the barium-impregnated liquids and the thickened and unthickened infant formula. This finding has important implications for the interpretation of the radiological results and subsequent clinical recommendations.