The Rheology of Liquids: A Comparison of Clinicians? Subjective Impressions and Objective Measurement

Abstract

Texture-modified diets are commonly prescribed for patients with dysphagia; it is therefore important to demonstrate that clinicians form accurate impressions of the rheological (flow) properties of the items that they recommend for their clients. We explored the correlation between objective rheological measurement and clinicians' subjective impressions of liquid consistency, rated on the bases of product labeling and sampling. Ten liquids, ranging from thin through nectar-thick and honey-thick to spoon-thick consistencies, were selected for study. Rheological analysis was conducted using a CarriMed CSL Controlled Stress Rheometer. Fifty speech-language pathologists ranked the liquids in order of perceived viscosity, based on their interpretation of the product packaging and label. Product nomenclature proved insufficient to accurately represent the consistency class to which each liquid belonged. A second group of 16 speech-language pathologists rated the perceived relative viscosity and density of nectar-thick and honey-thick juice items in blinded two-point discrimination tests of stirring-resistance, oral manipulation, and vessel weight. Physical sampling of these two products enabled clinicians to reliably perceive relative viscosity and density differences between the nectar- and honey-thick items.