Lubrication of saliva layer on oral and throat mucosa and its friction reduction effect of swallowing

Abstract

Swallowing disorder has been becoming a serious issue with increasing in elderly people. Disorder sometimes appears with a decrease in saliva, because saliva has an important role in lubrication over the oral cavity and throat. Though the structure of biological mucosa has been studied physiologically, there are only few studies that examined the influence of its oral and throat mucosa on fluid lubrication. Therefore, we investigated the friction reduction effect on the oral cavity and pharynx. There is a thin liquid phase with a thickness of about 0.1 mm called saliva layer on oral and throat mucosa. It is necessary to evaluate the rheological properties of mucus with low viscosity and high spinnability like saliva layer using a PEO solution, because of the viscosity characteristics different from the shear viscosity. The PEO solution concentration was determined from the measurement of the viscous characteristic by the rotational viscometer to set the same viscosity as that of saliva. Therefore, we investigated the rheological characteristics by measuring the extensional viscosity to make a mucus using a PVA coating. We measured friction torque on the artificial mucosa lubricated by PEO solution. The effect of torque reduction of friction by high-viscosity liquids (100% glycerin solution) on the artificial mucosa was clarified in this study. We considered apparent slip occurs in the saliva layer. However, there was no effect of friction reduction on the low viscosity (40% glycerin aqueous solution). Even if apparent slip occurs in the artificial mucosa, the viscosity on the artificial mucosa is the same as that of the liquids.