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Adam S Burbidge, Julie A. Y. Cichero, Jan Engmann, Catirona M. Steele
''A day in the life of the fluid bolus'': An introduction to fluid mechanics of the oropharyngeal phase of swallowing with particular focus on dysphagia.

Appl. Rheol. 26:6 (2016) 64525 (10 pages)

By following the path of a liquid bolus, from the oral preparatory phase to the esophagus, we show that a few fundamental concepts of fluid mechanics can be used to better understand and assess the importance of bolus viscosity during human swallowing, especially when considering dysfunctional swallowing (dysphagia) and how it can be mitigated. In particular, we highlight the important distinction between different flow regimes (i.e. viscosity controlled versus. inertia controlled flow). We also illustrate the difference between understanding bolus movements controlled by a constant force (or pressure) and those controlled by a constant displacement (or velocity). We limit our discussion to simple, Newtonian liquids where the viscosity does not depend on the speed of flow. Consideration of non-Newtonian effects (such as shear thinning or viscoelasticity), which we believe play an important part in human swallowing, requires a sound grasp of the fundamentals discussed here and warrants further consideration in its own right.

Cite this publication as follows:
Burbidge AS, Cichero JAY, Engmann J, Steele CM: ''A day in the life of the fluid bolus'': An introduction to fluid mechanics of the oropharyngeal phase of swallowing with particular focus on dysphagia., Appl. Rheol. 26 (2016) 64525.

Caroline E. Wagner, Alexander C. Barbati, Jan Engmann, Adam S. Burbidge, Gareth H. McKinley
Apparent shear thickening at low shear rates in polymer solutions can be an artifact of non-equilibration

Appl. Rheol. 26:5 (2016) 54091 (5 pages)

While shear thickening is a well-known feature of some polymer solutions, its observation in the absence of a clear specific chemical or structural mechanism and at very low rates of shear (shear rate ≤ 0.1/s) in our own data, as well as in several polymer systems in the literature, has prompted further investigation. Using the rheologically-reproducible and commercially available dysphagia product Resource√í Thicken Up Clear (produced by Nestle Health Science) as a canonical demonstration fluid, we show that the observation of a local maximum in the steady shear viscosity at very low shear rates can be completely attributed to the sample not having reached steady state conditions, and correspondingly, to the measurement not having been performed in steady simple shear flow. We propose two criteria to ensure equilibration during steady state flow rheological measurements: a substantial increase in the measurement time allotted for each point such that the total material strain accumulated in the sample is allowed to reach shear strain ≤ 5 and/or a stricter convergence criterion of 10 consecutive readings within a tolerance of 1%.

Cite this publication as follows:
Wagner CE, Barbati AC, Engmann J, Burbidge AS, McKinley GH: Apparent shear thickening at low shear rates in polymer solutions can be an artifact of non-equilibration, Appl. Rheol. 26 (2016) 54091.


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