Effect of Thickener Rheology on Bolus Cohesivity in Dysphagia Management

Dysphagia caused by dysfunction is commonly managed by thickened beverages, yet fluids with similar viscosity may differ markedly in terms of swallowing safety. This study investigates how thickening mechanisms such as viscosity level, elasticity, and shear-thinning affect bolus cohesivity and aspiration risk. Model fluids with identical shear viscosity at 50 s^-1 of 0.15 Pa s and IDDSI level 2 were formulated: Newtonian (maltodextrin), Boger (maltodextrin + xanthan, elastic), and shear-thinning (xanthan). Their flow behavior was evaluated in a swallowing simulator ("The Gothenburg Throat") replicating healthy and impaired conditions, combined with shear and extensional rheometry. Despite identical shear viscosity, marked differences in flow were observed. Newtonian fluids showed insufficient cohesivity and allowed aspiration under impaired conditions, whereas both elastic (Boger) and shear-thinning fluids maintained cohesive boluses and prevented airway entry. Elastic and extensional properties enhance bolus integrity, reducing droplet breakup. Analysis using dimensionless numbers indicated that neither viscosity nor inertia alone predicts performance; instead, a combined "bolus cohesivity number" incorporating viscous, elastic, inertial, and surface forces correlated with aspiration outcomes. These results demonstrate that the mechanism of thickening is critical: elasticity and shear-thinning improve swallowing safety beyond viscosity alone, which has strong implications for the design and selection of dysphagia thickeners.