Viscosity Measurements of Nectar- and Honey-thick Liquids: Product, Liquid, and Time Comparisons

This study compared the viscosity (thickness) of five different liquids thickened to nectar- or honey-like consistencies with a variety of thickening products. Samples were prepared using manufacturer guidelines and viscosity was measured at the recommended time to thicken (standard) and also after 10 and 30 min. Centipoise (cP) measurements of the samples were compared across products and within product lines for each level of thickness at all three time periods. Statistical analysis showed that the viscosity of a nectar- or honey-like liquid was highly dependent on the type of thickening product and the time it was allowed to thicken. Variability in viscosity measurements also was noted within a product line for thickening various liquids. Results are discussed in relation to the National Dysphagia Diet guidelines for nectar- and honey-like consistencies.     

The Usefulness of the Line Spread Test as a Measure of Liquid Consistency

Although dietary modification is a common treatment strategy used to manage dysphagic patients who aspirate thin liquids, there are no standard definitions for thickened liquid preparation. This lack of standardization leads to variability in practice and points to the need for a simple tool for clinicians to assess thickened liquid consistency. The current study analyzed the utility of the Line Spread Test (LST) in this regard. Twenty-six liquids (10 powder-thickened "nectar" juices, 10 powder-thickened "honey" juices, and 6 barium mixtures) were assessed using both a viscometer for objective measurement of viscosity and the LST. Whereas the LST was able to separate the juices into nectar and honey categories, it was not able to separate barium mixtures into these categories nor compare barium to juices. Furthermore, the LST was not predictive of viscosity. Thus, the results of the current study suggest that the LST may be useful in the broad categorization of fluids into therapeutically significant groupings but that it cannot be used more specifically to measure fluid viscosity. Further studies of this and other tools are necessary to identify inexpensive practical tools for quantification of thickened liquid consistency.     

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.     

Thickener Viscosity in Dysphagia Management: Variability among Speech-Language Pathologists

Twenty-three speech-language pathologists (SLPs) experienced with thickening liquids for dysphagia evaluations were asked to mix solutions comparable to their perceptions of nectar, honey, and pudding consistencies. The purpose of the study was to determine if these professionals were able to reliably repeat their relative perceptions of nectar, honey, and pudding over multiple mixings. Each mixed solution was analyzed using a viscometer to determine its actual viscosity. A replication reliability analysis indicated that the professionals were not consistent in their attempts to thicken liquids. Intrasubject results were somewhat better or more consistent than intersubject results. Results of this study indicate the need for a standard protocol during dysphagia management to ensure consistent viscosities across evaluation and treatment.     

Are We Testing a True Thin Liquid?

The purpose of this study was to examine the effects on a patient’s swallowing of diluting E-Z-EM’s Varibar^® Thin liquid barium product (which is often used in videofluoroscopic swallow studies) to achieve a consistency closer to water. Forty patients who were 18 years and older participated in this study. Their varied medical diagnoses included stroke, pneumonia, TBI, and cancer as well as diagnoses not usually associated with dysphagia such as abdominal pain and rhabdomyolysis. To screen for aspiration, E-Z-EM’s Varibar Thin liquid was presented to patients to swallow as 2 cc, 5 cc, cup, and straw drinking trials. If no aspiration occurred, the patient was given the Varibar Thin liquid diluted by 50% using water (referred to as Ultrathin) to swallow in the same amounts. Then occurrence of aspiration with the Ultrathin liquid was compared to the occurrence of aspiration when the patient swallowed the Varibar Thin liquid. Fifty percent of patients aspirated on the Ultrathin liquid but not on the Varibar Thin liquid, across at least one of the test conditions. From these results we suggest that although E-Z-EM Varibar Thin liquid may have a low-viscosity range, it still may not be “thin enough” to identify all patients who aspirate or who are at risk for aspiration on thin liquids.     

Viscosity measurements of barium sulfate mixtures for use in motility studies of the pharynx and esophagus

Detailed viscosity measurements have been made of barium sulfate mixtures over a wide range of viscosities for use in radiography of the esophagus, stomach, and duodenum. A new methodology was developed for more accurate estimation of viscosity in non-Newtonian fluids in conventional cylinder-type viscometers. As base cases, the variation of viscosity with shear rate was measured for standard commercial mixes of e·z·hd (250% w/v) and a diluted mixture of liquid e·z·paque (40% w/v). These suspensions are strongly shear thinning at low shear rates. Above about 3s⁻¹ the viscosity is nearly constant, but relatively low. To increase the viscosity of the barium sulfate mixture, Knott's strawberry syrup was mixed to different proportions with e·z·hd powder. In this way viscosity was systematically increased to values 130,000 times that of water. For these mixtures the variation of viscosity with temperature, and the change in mixture density with powder-syrup ratio are documented. From least-square fits through the data, simple mathematical formulas are derived for approximate calculation of viscosity as a function of mixture ratio and temperature. These empirical formulas should be useful in the design of “test kits” for systematic study for pharyngeal and esophageal motility, and clinical analysis of motility disorders as they relate to bolus consistency.     

Viscosity Is Not a Parameter of Postdeglutitive Pharyngeal Residue: Quantification and Analysis with Scintigraphy

The aim of this study was to explore the influence of viscosity on pharyngeal residue in normal healthy volunteers. Scintigraphy was used to measure pharyngeal residue in 11 healthy volunteers after swallowing three different substances (age = 20.2–48.3 years). The first substance was a 10-ml solution of tap water with 0.5% xanthan with a viscosity of 4500 mPa s, comparable to a yogurt drink. The second and third substances were a 0.75% xanthan and a 1.00% xanthan solution, with viscosities of 10,500 and 21,000 mPa s, comparable to low-fat yogurt and 3% fat yogurt, respectively. Tap water was used as the control substance. Mean pharyngeal residue after swallowing tap water was 2.3% (SD = 1.2) of the initial volume in the oral cavity. Pharyngeal residue after swallowing 0.5% xanthan solution was 1.8% (SD = 0.8), after swallowing 0.75% xanthan solution 2.6% (SD = 2.2), and after swallowing 1.00% xanthan solution 2.8% (SD = 1.7). No significant correlation between increase of viscosity and pharyngeal residue was found. In healthy persons viscosity does not seem to be a significant parameter for pharyngeal residue for boluses with viscosities ranging from tap water to solutions having a viscosity comparable to 3% fat yogurt.     

The Rheology of Liquids: A Comparison of Clinicians’ Subjective Impressions and Objective Measurement

Texture-modified diets are commonly prescribed for patients with dysphagia; it is therefore important to demonstrate that clinicians form accurate impressions of the rheological (flow) properties of the items that they recommend for their clients. We explored the correlation between objective rheological measurement and clinicians subjective impressions of liquid consistency, rated on the bases of product labeling and sampling. Ten liquids, ranging from thin through nectar-thick and honey-thick to spoon-thick consistencies, were selected for study. Rheological analysis was conducted using a Carri-Med CSL Controlled Stress Rheometer. Fifty speech-language pathologists ranked the liquids in order of perceived viscosity, based on their interpretation of the product packaging and label. Product nomenclature proved insufficient to accurately represent the consistency class to which each liquid belonged. A second group of 16 speech-language pathologists rated the perceived relative viscosity and density of nectar-thick and honey-thick juice items in blinded two-point discrimination tests of stirring-resistance, oral manipulation, and vessel weight. Physical sampling of these two products enabled clinicians to reliably perceive relative viscosity and density differences between the nectar- and honey-thick items.     

Effects of systematic bolus viscosity and volume changes on hyoid movement kinematics

Using ultrasonography with head and transducer stabilization, this study examined the effects of maximally controlled, systematic changes in bolus viscosity (thin juice-like, 7 cP; nectar-like, 243–260 cP; honey-like, 724–759 cP; spoon-thick, 2760–2819 cP) and volume (5, 10, 20, 30 cc) on hyoid kinematics in 31 healthy subjects (16 male, 15 female) in three age groups (20–39, 40–59, 60–79 years). Frame-by-frame hyoid displacements were tracked from digitized images of 612 swallows. Measures of movement durations, maximal amplitudes, total distances, and peak velocities were subjected to repeated measures multivariate analyses of variance with viscosity, volume, age, and gender as factors. Results showed that (1) spoon-thick swallows had the greatest preswallow gesture and total movement durations; (2) larger-volume swallows had significantly greater maximal amplitudes, forward peak velocity, and total vertical distance; (3) older subjects had longer start-to-max duration (though shorter preswallow gesture and total movement durations), greater maximal vertical amplitude, longer total vertical distance, and greater backward peak velocity than younger subjects; (4) males had greater values for all kinematic parameters except preswallow gesture, hyoid-at-max, and max-to-end durations. The results illustrate the importance of examining the interrelations among kinematic variables to better understand task accommodation and motor control strategies. The evidence also supports the concept of suprahyoid–infrahyoid functional adaptation and compensation in the healthy elderly.     

Viscosity effects on EMG activity in normal swallow

This study investigated the effects of six consistencies on measures of swallow duration, muscle activity, and sound. Electromyographic (EMG) recordings of the submental and infrahyoid muscle complexes, and audio recordings of neck sounds were made while 5 normal subjects swallowed two foods in each of three consistency categories: liquid, thin paste, and thick paste. Total swallow duration, measured from EMG, increased significantly across consistency categories from liquids to thin pastes to thick pastes. Liquids and thin pastes were significantly different from thick pastes on all but one EMG measure. However, liquids and thin pastes failed to reach significance on any of the EMG measures. EMG activity in the submental muscles most often initiated the swallow whereas the infrahyoid muscle activity most frequently terminated the swallow. A sound spike occurred at relatively the same time in each swallow. Results are discussed in terms of systematic modulations of muscle activity during swallow.     

Temporal Measurements of Pharyngeal Swallowing in Normal Populations

The purpose of this investigation was to examine the temporal differences among three measures of pharyngeal stage transition in 40 normal subjects. The measures were (1) Pharyngeal Delay Time (PDT), (2) Stage Transition Duration (STD), and (3) Delayed Pharyngeal Swallow (DPS). Results showed a significant difference between younger and older subjects for PDT and STD but not for DPS. No gender differences were observed. These data on normal subjects will be used for comparisons with stroke patients in future research. This work was performed at the University of Tennessee, Knoxville, Tennessee.     

Chewing and Food Consistency: Effects on Bolus Transport and Swallow Initiation

Preswallow bolus formation usually occurs in the mouth for liquids and in the oropharynx for solid foods. We examined the effect of chewing on the relationship between bolus transport and swallow initiation. Fifteen healthy subjects were imaged with lateral projection videofluorography while eating liquids, solid foods, and a mixture of liquid and solid foods in upright and facedown postures. Videotapes were reviewed to measure the location of the leading edge of the barium at swallow initiation. Chewing and initial consistency each altered the relationship between food transport and swallow initiation. In particular, when chewing liquid (or consuming foods with both liquid and solid phases), a portion of the food commonly reached the hypopharynx well before swallow onset. This transport to the hypopharynx was highly dependent on gravity, but transport to the valleculae for chewed solid food was active, depending primarily on tongue-palate contact. Chewing appeared to reduce the effectiveness of the posterior tongue-palate seal, allowing oral contents to spill into the pharynx. Consuming two-phase foods with both solid and liquid phases may increase the risk of aspiration in dysphagic individuals with impaired airway protective reflexes.     

Temperature acceleration in cold oral stimulation

This study measured the temperature acceleration of a cold probe as it contacts human tissue. Both the effects of touching a cold probe to the oral cavity and maintaining contact of the cold probe with the oral cavity were investigated. The results indicated a rapid warming pattern. This warming is effected first by temperature changes resulting from the probe being moved from ice into room temperature and second by the contact to oral mucosa. In fact, in some cases, the probe had reached minimal cold sensation levels by the time it reached the oral cavity. Results also indicated that 6 sec after the probe is lifted from the ice, the temperature closely aproximates temperatures perceived as warm or at least neutral, but not cold.This investigation was supported in part by Veterans Administration Merit Review (Research Advisory Group) grant #331.     

Time-Dependent Rheology of Starch Thickeners and the Clinical Implications for Dysphagia Therapy

The viscosity of nonsolid foods and the stability of their viscosity over time is critical in managing dysphagia. The time-dependent viscosity of liquids thickened with starch-based thickeners was measured at constant temperature and shear rate. Viscosity was measured between 30-min intervals of rest (zero shear) over a period of 17 h at 20.0°C. Two common types of thickeners were evaluated: maize-based and maltodextrin-based (the latter commonly used in pediatrics). The maize-based thickeners undergo a significant decrease in viscosity over the initial 1–4 h following preparation. The maltodextrin-based thickener’s viscosity increases significantly 30 min following preparation and is then more stable over time than its maize-based equivalent. These findings suggest that the success of current dysphagia therapies that use thickeners could be influenced by the time-dependent nature of thickened fluid viscosity. Acknowledgment and appropriate selection of the thickener type is shown to be of great importance.     

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.     

Computerized thermistor technique for indirect studies of esophageal blood flow

The aim of this study was to elaborate on a computerized microthermistor technique for indirect measurement of esophageal blood flow and to investigate if any changes in circulation could be found in patients who are provoked by esophageal acid perfusion of their acid-sensitive mucosa. A thermistor was mounted in a plastic catheter and placed in the esophagus 11 cm above the lower esophageal sphincter. The signal from the thermistor was transmitted to a personal computer. A 15°C water bolus was injected into the catheter in order to cool the esophageal wall at the catheter side hole 1 cm above the thermistor. The reliability of the thermistor test was examined by repeating it in 29 patients. No statistical difference between the two test occasions was found. Twenty-five patients were provoked with an acid perfusion test, 14 of whom had a positive reaction with heart-burn. Patients with a positive acid perfusion test had a shorter rewarming time before as well as after provocation than patients with a negative acid perfusion test. It is concluded that this thermistor technique, is well suited for measuring intraluminal rewarming rate as an indirect sign of changes in esophageal blood flow. Furthermore, the results indicate that blood supply of the esophageal wall is increased in patients with a positive acid perfusion test.     

Nonsurgical treatment of drooling in a patient with closed head injury and severe dysarthria

The purpose of this investigation was to measure the effectiveness of the antimuscarinic drug atropine sulfate in the treatment of chronic drooling in a patient with a history of severe closed head injury and resultant widespread oral neuromuscular and higher cortical disturbances. Results of the A-B-A-B-A-B withdrawal paradigm, chosen to demonstrate the functional relationship between drug therapy and the degree of drooling, revealed that administration of atropine sulfate reduced by more than 50% of baseline levels the amount of resting secretion, intraoral accumulation, and pharyngeal-laryngeal pooling of saliva, with negligible side effects. These results are discussed and compared to the alternative drug and surgical approaches to the alternative drug and surgical approaches to treatment that have been the primary focus of recent research on drooling.     

Multiple swallows and piecemeal deglutition; Observations from normal adults and patients with head and neck cancer

The incidence of multiple swallows for liquid and paste, and the time delay between multiple swallows, was determined from videofluoroscopic records of modified barium swallow tests. In a comparison of liquid and paste, the overall incidence of multiple swallows did not differ, for either patients with head and neck cancer or normal controls. However, for liquid swallows the incidence in patients with cancer was abnormally high, predominantly in patients with pharyngeal cancer.     

Laryngeal Penetration During Deglutition in Normal Subjects of Various Ages

This study examined the frequency of penetration of liquid, paste, and masticated materials into the airway during videofluoroscopic studies of normal swallow in 98 normal subjects who were from 20 to 94 years of age. The purposes of the study were to define frequency and level of penetration using the penetration-aspiration scale as a result of age, bolus volume, viscosity, and gender, and to describe the body's sensorimotor response to the penetration based on audible coughs or throat clearing on the audio channel of each videotaped fluoroscopic study. Frequencies of penetration were defined in relation to bolus volume, age, gender, and bolus viscosity from swallows of 1, 3, 5, and 10 ml and cup-drinking of thin liquids; 3 ml of pudding; (1/4) of a Lorna Doone cookie; and a bite of an apple. Results showed that penetrations were significantly more frequent after age 50 and thick viscosities penetrated only in subjects age 50 and over. For persons under 50, 7.4% of swallows exhibited penetration, while for people age 50 and over, 16.8% of swallows showed penetration. Significantly more penetration occurred on larger liquid boluses. There was no relationship between gender and frequency of penetration. None of the subjects that penetrated showed a sensorimotor response to the penetration, which may relate to the relatively shallow depth of the penetration.