Rheology of Barium Sulfate Suspensions and Pre-thickened Beverages Used in Diagnosis and Treatment of Dysphagia

Pre-thickened beverages and barium sulfate suspensions are used in the treatment and diagnosis of dysphagia. These liquids are labeled nectar consistency (NC), honey consistency (HC) etc. These labels are rather misleading and do not represent the actual rheological character of the liquids. We carefully investigated the rheology of these liquids to assist both in their formulation and use for dysphagic patients. Steady state flow properties, thixotropy, dynamic response, and creep recovery behavior were investigated for six beverages and two barium sulfate suspensions. All samples exhibited a shear-thinning behavior. The flow curves of all samples followed both Herschel-Bulkley and Casson models. HC barium sulfate suspension exhibited higher yield stress, σo, and higher storage modulus, G’, than their fluid food counterparts. In contrast, NC barium sulfate suspension had lower σo, and G’ than some of the liquid food counterparts. Frequency spectra of NC samples were similar to that of a macromolecular solution with both G’ and loss modulus, G’’, increasing with frequency; whereas those of HC samples were similar to that of a gel with a little dependency of G’ and G’’ over frequency. Stress sweep experiments showed that the linear viscoelastic region of fluid foods and barium sulfate suspensions extended up to 1 and 10 Pa, respectively. Thus, significant differences exist in the rheological properties of both pre-thickened and videofluoroscopy fluids currently used for diagnosis and treatment of dysphagia.