Oral Perceptual Discrimination of Viscosity Differences for Non-Newtonian Liquids in the Nectar- and Honey-Thick Ranges

Abstract

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.

A review of diet standardization and bolus rheology in the management of dysphagia

“…Different beveragethickener combinations can exhibit large differences in shear-thinning behaviour resulting from the interaction of starch, gums and juice particulates; this could confuse patients [11*]. It is interesting that materials may be perceived differently despite absence of significant differences in in-mouth pressure-bulb measurements [10*], [12]: this may reflect the tongue being more sensitive than the pressure-bulb, or, that the pressures required to propel these (relatively low-viscosity and low-mass) liquid boluses are quite small compared to the baseline pressure involved in accelerating the tongue itself and creating a lingual-palatal seal.…”

Fonoaudiologia e nutrição em ambiente hospitalar: análise de terminologia de classificação das consistências alimentares

“…Authors observed that the number of consistencies differentiated by subjects was higher than what the classifications recommend. Nevertheless, insofar, as viscosity increases, only great variations are found (24) . Before suggesting any classifications, it would be interesting to conduct studies that discussed what viscosity differences are clinically relevant to cause physiological or functional changes in swallowing.…”

“…These classifications, based on the measured value of food rheological characteristics, would be convenient to exclude any confusion in food prescriptions. Hence, it is important that such pieces of information be present in packages and labels of commercially available products (24) . The classification used in Japan adds not only texture but also energy and protein content, hardness, and cohesion for each consistency and temperature (15 or 45°C) (3) .…”

Understanding the Rheological Parameters of Thickened Fluids for Dysphagia Sufferers

“…Additionally, the range should have a distinct band gap between each level, as otherwise a difference of only 1 mPa.s, which is much smaller than any difference that could be seen either clinically or experimentally, would lead to a fluid falling 'into range' or 'out of range' (Smith et al, 2006, Steele et al, 2014a.…”

“…For long-term management, texture modification of foods and fluids play a major role in clinicians' treatment (Leonard andKendall, 2013, Cichero et al, 2013). It has been reported that prescription of thickened fluids has become one of the most common recommendations made by clinicians to address the effects of dysphagia (Mills, 2008, Steele et al, 2014a. Thickened fluids flow slowly, allowing better oral and pharyngeal coordination and thus enhance safe swallowing (Reimers-Neils et al, 1994).…”