Levator Veli Palatini Muscle Activity during Swallowing Non-Newtonian Fluid

Abstract

Purpose: The transition between oral and pharyngeal phases is one of sites of misswallowing of lowviscosity liquids. Thickening agents are commonly used to prevent the airway from misswallowing and/or aspiration of low-viscosity liquids. In some cases, however, clinical demands cannot be satisfied partly because the transition phase cannot be adequately regulated due to shear-rate dependent viscosity of a liquid containing a thickening agent. Velopharyngeal function, in which the velum is primarily involved, plays a major role in regulating the transition phase between oral and pharyngeal phases. The purpose of the current study was to electromyographically clarify the following: 1) how velopharyngeal function during swallowing non-Newtonian fluids can be regulated, and 2) which has a greater impact on muscle activity, shear-rate dependent viscosity or viscosity measured using a B-type viscometer with rotor rotation speed of 12 rpm.

Methods: Ten healthy subjects (mean±SD: 24±2 y) without any clinical history of dysphagia joined the study. Smoothed EMG signals of the levator veli palatini (LVP) muscle were collected. Three test materials were prepared by mixing a thickening agent into commercially-available green tea as follows: two test materials had similar shear-rate dependent viscosity which was higher for one material in the range of shear rate greater than 2/s although the three materials showed a similar measure of viscosity obtained using the B-type viscometer with rotor rotation speed of 12 rpm. Each subject swallowed a certain volume of three materials 10 times, respectively. The swallowing volume was individually determined on the basis of the optimum volume for swallowing for each subject.

Results: LVP muscle activity was significantly greater for one material with a lower shear rate viscosity while two materials with similar shear rate viscosity showed smaller EMG values which were not significantly different between each other.

Conclusion: It was clarified that the velopharyngeal function for swallowing non-Newtonian fluids could be regulated according to the difference in shear-rate dependent viscosity, not with the viscosity obtained by the B-type viscometer with rotor rotation speed of 12 rpm.