Flow Characteristics of Barium Thickened Liquids during Swallowing in Healthy Adults

Modification of liquid viscosity complying with the International Dysphagia Diet Standardisation Initiative (IDDSI) framework is crucial in managing swallowing difficulties in individuals with dysphagia. Despite having similar viscosities, different thickening agents may exhibit varied extensional properties, potentially influencing bolus formation and the movement of oropharyngeal and hyolaryngeal structures during swallowing. This study aims to evaluate the effects of various thickening agents on swallowing behaviour and the extensional properties of boluses across IDDSI levels 1 to 4, using the Videofluoroscopic Swallowing Study (VFSS). Thirty healthy participants consumed 10 mL of liquids thickened with five different thickening agents, prepared at each IDDSI level 1 to 4, during VFSS. The bolus head during swallowing onset, the movement of oropharyngeal and laryngeal structures and the bolus aspect ratio (BAR) were analysed across different thickening agents. With increasing IDDSI levels, the bolus was observed at progressively higher anatomical levels-residing in the valleculae or hypopharynx at IDDSI level 1, and in the oral cavity at IDDSI level 3 and IDDSI level 4. Laryngeal closure duration (LCD) significantly decreased with increasing IDDSI levels (from 1 to 3 and 4). In addition, ThickenUp^® Clear (TUC) yielded the highest LCD among all thickening agents. The BAR remained stable across IDDSI levels and thickening agents, with no significant differences noted. In healthy adults, thicker consistencies positioned the bolus higher in the oropharynx and prolonged laryngeal closure, supporting safer swallowing. Gum-based thickeners produced more cohesive and stable boluses than starch-based agents, allowing more controlled bolus flow and airway protection.