Flow properties of oral contrast medium formulations depend on the temperature

Purpose: To study the rheological exploration (variation of viscosity with temperature) of thickened food used for radiologic swallowing examinations in patients with oral and pharyngeal dysfunction, in particular in mixtures of barium sulfate suspensions and in iodine solutions.Material and Methods: Deep-frozen mango puree was thawed at room temperature. It was then mixed with barium sulfate contrast medium to a density of 25% w/w. Resorce (R) Thicken Up was mixed at room temperature at two concentrations: 4.3% w/w (4.5 g thickener + 100 g distilled water) and 6.0% w/w (4.5 g thickener + 70 g distilled water). The thickener consisted of modified corn starch. Resorce (R) Thicken Up was also mixed at room temperature with two concentrations of an iodine contrast material, iohexol (Omnipaque (R), 350 mg I/ml). The two concentrations were: 4.3% w/w (4.5 g thickener + 100 g iohexol) and 6% w/w (6 g thickener + 100 g iohexol). Measurements were carried out from 20 degrees C to 37 degrees C using a Stresstech HR rheometer. The rheometer was equipped with a concentric cylinder measuring system (inner cylinder 15 mm).Results: The samples containing thickener in water as well as in iohexol showed a dependence on thickener concentration and temperature. The mango puree with barium sulfate displayed very small temperature dependence. The thickener solutions in iohexol had significantly higher viscosity compared with the other thickener solutions and the mango puree. The relative decrease shows that mango puree, the 6% thickener solution in water, and solutions with iohexol exhibited similar relative viscosity change at different temperatures.Conclusion: Our conclusion is therefore that it is important always to make the solution with high precision. It is also of importance to observe how long the patient keeps the bolus in the mouth. This might vary and actually it may not be possible to influence this factor. When different types of thickeners are compared, it is important to take into account the temperature at which the thickener is observed.