Mechanical Engineering, University College London (UCL), London, UK.
Int J Lang Commun Disord. 2011 Jan-Feb;46(1):17-29. doi: 10.3109/13682822.2010.484846. Epub 2010 Jun 21.
In dysphagia care, thickening powders are widely added to drinks to slow their flow speed by increasing their viscosity. Current practice relies on subjective evaluation of viscosity using verbal descriptors. Several brands of thickener are available, with differences in constituent ingredients and instructions for use. Some thickened fluids have previously been shown to exhibit time-varying non-Newtonian flow behaviour, which may complicate attempts at subjective viscosity judgement.
The aims were to quantify the apparent viscosity over time produced by thickeners having a range of constituent ingredients, and to relate the results to clinical practice.
METHODS & PROCEDURES: A comparative evaluation of currently available thickener products, including two which have recently been reformulated, was performed. Their subjective compliance to the National Descriptors standards was assessed, and their apparent viscosity was measured using a rheometer at shear rates representative of situations from slow tipping in a beaker (0.1 s⁻¹) to a fast swallow (100 s⁻¹). Testing was performed repeatedly up to 3 h from mixing.
OUTCOMES & RESULTS: When mixed with water, it was found that most products compared well with subjective National Descriptors at three thickness levels. The fluids were all highly non-Newtonian; their apparent viscosity was strongly dependent on the rate of testing, typically decreasing by a factor of almost 100 as shear rate increased. All fluids showed some change in viscosity with time from mixing; this varied between products from -34% to 37% in the tests. This magnitude was less than the difference between thickness levels specified by the National Descriptors.
CONCLUSIONS & IMPLICATIONS: The apparent viscosity of thickened fluids depends strongly on the shear rate at which it is examined. This inherent behaviour is likely to hinder subjective evaluation of viscosity. If quantitative measures of viscosity are required (for example, for standardization purposes), they must therefore be qualified with information of the test conditions.
在吞咽障碍护理中，通过增加液体的黏度来减缓其流速，广泛将增稠剂添加到饮料中。目前的做法依赖于使用描述性语言对黏度进行主观评估。有几种品牌的增稠剂可供选择，其成分和使用说明存在差异。一些增稠的液体以前被证明具有时变的非牛顿流动行为，这可能会使主观黏度判断复杂化。
目的是量化具有不同成分的增稠剂随时间产生的表观黏度，并将结果与临床实践联系起来。
对目前可用的增稠剂产品进行了比较评估，包括两种最近重新配方的产品。评估了它们对国家描述符标准的主观符合程度，并使用流变仪在代表从在烧杯中缓慢倾斜（0.1 s⁻¹）到快速吞咽（100 s⁻¹）的各种情况下的剪切率下测量它们的表观黏度。测试在混合后 3 小时内重复进行。
当与水混合时，发现大多数产品在三个厚度水平上与主观国家描述符相比都很好。这些流体都是高度非牛顿的；它们的表观黏度强烈依赖于测试的速率，通常随着剪切率的增加，黏度降低近 100 倍。所有的流体从混合开始都有一定的时间黏度变化；在测试中，这种变化在产品之间的差异从-34%到 37%不等。这种幅度小于国家描述符规定的厚度级别之间的差异。
增稠流体的表观黏度强烈依赖于检查时的剪切率。这种固有行为可能会阻碍对黏度的主观评估。如果需要对黏度进行定量测量（例如，用于标准化目的），则必须在测试条件下对其进行限定。
