Flow properties of oral contrast medium formulations depend on the temperature

During the therapeutic videofluoroscopic examination of swallowing, gradation of bolus volume, texture, and viscosity can be implemented to determine the optimal bolus characteristics in that particular patient. When a thickened liquid is given to a dysphagic patient it is served at room temperature. However, in these patients with a delayed oral and/or pharyngeal stage of swallow, the bolus is held for a long time in the oral cavity. The temperature of the thickened liquid thereby increases.

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.

Deep-frozen mango purée was thawed at room temperature. It was then mixed with barium sulfate contrast medium to a density of 25% w/w. Resorce 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 Thicken Up was also mixed at room temperature with two concentrations of an iodine contrast material, iohexol (Omnipaque, 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).

The samples containing thickener in water as well as in iohexol showed a dependence on thickener concentration and temperature. The mango purée 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 purée. The relative decrease shows that mango purée, the 6% thickener solution in water, and solutions with iohexol exhibited similar relative viscosity change at different temperatures.

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.