Thickened liquids are often recommended for people with swallowing dysfunction (dysphagia). During instrumental swallowing assessment, barium sulfate and saline are added to these liquids for radiopacity and signal conductivity. Although assumed to mimic everyday nutritional beverages, the addition of such agents may change their rheology, challenging this assumption. This study aimed to determine the effect of barium sulfate, thickener type, and saline on the rheological properties of liquids used for instrumental swallowing assessment. Liquids were prepared with combinations of barium sulfate, thickeners, and saline. Shear viscosity, extensional viscosity, yield stress, and surface tension were measured. Optical light microscopy was used to analyze the internal structure of all liquids. A 23 factorial design was developed, and statistical analyses included multivariate linear regression, three-way ANOVA, and Pearson's correlation coefficients. Shear viscosity at 50 s-1 increased when barium and starch thickener were present. Extensional viscosity increased when the combination of barium, starch, and saline was present. All added ingredients affected the breakup time. Yield stress and surface tension both decreased when the combination of barium and saline was present. Shear viscosity correlated negatively with extensional viscosity and surface tension, while extensional viscosity and breakup time were positively correlated with yield stress. In conclusion, barium sulfate and thickener type modified all rheological parameters. While barium is mandatory for videofluoroscopy, the flow properties of thickened liquids may be affected, thereby influencing the validity of findings obtained during videofluoroscopy. Future work will examine how changes in these rheological parameters influence swallowing function in adults.
Keywords: Dysphagia; extensional viscosity; shear viscosity; surface tension; thickeners; yield stress.