Rheological aspects of swallowing and dysphagia: Shear and elongational flows

Abstract

The physiological process of swallowing is not only a simple transfer of liquids or food boluses from the oral cavity to stomach, but also a complex succession of voluntary and involuntary phases that involve complex deformations and require the entire functionality of the oropharyngeal apparatus. When this functionality is affected, people experience dysphagia, which is described as a combination of symptoms that impairs or reduces patient’s ability to swallow. On the other hand, food texture also plays an important role in swallowing. Each liquid viscosity or bolus consistency is processed differently in the mouth and it requires a specific amount of lubrication and effort in order to be easily and safely swallowed. The science of rheology deals specifically with the deformation and the flow of matter. Therefore, rheology helps to characterise food behaviour in complex deformations, such as those encountered during swallowing. The knowledge of the deformability and flow of the bolus is particularly important in understanding and managing dysphagia. In this chapter, a short introduction on dysphagia is given. Section “Rheology Fundamentals” is dedicated to the science of rheology and provides a short description of the material functions relevant to this field. Dysphagia-designed products are used as examples. Section “Rheology, Swallowing and Dysphagia: State-of-the-Art” focuses on the rheological aspects of bolus oral processing and transport. A practical example on how shear rheology helps to tailor new dysphagia products is also included. Aspects about the role of extensional rheology in the swallowing are introduced. This section is followed by the rheological characterisation of different nutritional products in the presence of saliva. The role of human saliva in the management of dysphagia is as well discussed. The chapter ends with some concluding remarks.