Theoretical Estimation of Shear Rate during the Oral Phase of Swallowing: Effect of Partial Slip

The goal of this study was to quantify the shear rate in a simplified model of the oral cavity during bolus ejection. Parallel plate squeezing flow was used to approximate the action of the tongue against the palate as a bolus is ejected from the mouth and into the pharynx during a swallow. The current work quantified variations in shear rate with respect to two main effects – the relative degree of boundary slip for Newtonian boluses of varying viscosity. The results suggest that a single shear rate that describes oropharyngeal swallowing is a too simplistic concept. Rather variation in bolus viscosity, level of lubrication as well as others may have a strong effect on shear rate. Practical Applications Mathematical modeling of oropharyngeal swallowing has the potential to play an important role in understanding the underlying mechanics of normal and abnormal swallowing, as well as in guiding the development and optimization of therapeutic strategies for swallowing disorders. The long-term objective of this research is to develop a robust methodology for prediction of bolus flow characteristics in response to motions of the oropharyngeal structures, such as the tongue and pharyngeal walls. In addition to furthering our understanding of the normal swallow, such models could probe the physical basis of biomechanical treatment strategies, such as postural changes (e.g., chin-tuck) or dietary medications (commonly referred to as “thickened liquids”), as well as optimizing such strategies or suggesting new strategies altogether.