An In-Vitro Simulator to Study Non-Newtonian Fluid Mechanics During the Oral Phase of Swallowing

This thesis describes the design and evaluation of a mechanical oral model and its application to investigate flow of thickened fluids used in the management of swallowing disorders, “dysphagia”. Following a review of current dysphagia and swallowing literature, three research questions were proposed: What are the pressures required to clear a thickened fluid bolus from the oral cavity? What range of shear rates are measured in a thickened fluid bolus during the oral stage of swallowing? What is the best method to classify consistency in regard to ease of swallow in the mouth? In operation, the model compresses a fluid bolus between a compliant tongue and hard palate. Key mechanical parameters were chosen to replicate physiological values: sagittal tongue dimensions 70 x 60 mm (length x height), tongue elastic modulus 122.5 kPa, tongue-palate contact pressure 2 - 36 kPa, oral stage duration 320 - 3036 ms and bolus volume 2 - 15 ml. Five sensors measured intrabolus pressure along the median line of the palate surface. A particle image velocimetry (PIV) system was created in order to measure intrabolus flow and the resulting 2D velocity maps were used to calculate shear rates throughout the bolus during the simulated swallows. Experiments compared starch and gum thickened fluids at four concentrations based on the IDDSI scale for clinical fluid consistency. As concentration was increased the pressure required to clear a bolus increased from 0.14 to 4.5 kPa. Bolus shear rate varied from 0 centrally to a maximum at the tongue and palate surfaces. The maximum could not be measured, but it exceeded 12 to 28 s-1. This work explored the use of an in-vitro model to investigate the fluid dynamics of swallowing. Results improve the current understanding of the oral phase of swallowing and may help improve therapeutic treatments for dysphagia