Role of Rheology in Swallowing

In basic terms, the swallowing process may be modeled (Chang et al., 1998) considering that the human throat is an axisymmetric pipe with moveable walls as shown 

Flow Rate and Cumulative Volume for a Newtonian Fluid 

For a Newtonian water bolus with a viscosity of 0.001 Pa s and a density of 1,000 kg m , the initial normal stress at the GPJ had to be reduced by 92% (from 150 to 12 mmHg) and the duration at which the initial normal stress was held was reduced by 69% (from 0.32 to 0.1 s) in order for the model to simulate a 20-mL swallow. Not using these corrections resulted in reverse flow (i.e., negative flow rate) at the GPJ. This was reasonable because the water bolus has a smaller viscosity than the other two liquids. Reverse flow may occur in the human throat if the pharyngeal 

Calculated values of the apparent viscosity ( )a) of the shear-thinning non-Newtonian bolus at the UES showed a rapid drop from an initial viscosity of 60 Pa s 

These data suggest that perhaps one reason shear-thinning non-Newtonian liquids are safer to swallow than thin Newtonian liquids is due to the reduced fluid flow during the second half of the swallowing process. The reduced flow in turn allows more time for air passages (e.g., entry to the trachea or the nasopharynx) to completely shut off prior to the arrival of food. Asa result, the dysphagic patient does not aspirate as he or she would with a Newtonian bolus. 

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Chapter 7. Comparison of oral and non-oral assessment techniques. Role of rheology in swallowing—results of computer simulation. Rheological aspects of creaminess. 

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