Effect of Thickened Fluids on Swallowing Function in Oropharyngeal Dysphagia: Impact of Shear Rheology and Disorder Subtype

Introduction Fluid thickeners used in the management of oropharyngeal dysphagia exhibit non-Newtonian shear-thinning rheology, impacting their viscosity during deglutition. This study investigated how the rheological properties of thickened fluids affect pharyngeal swallowing parameters in patients with oropharyngeal motor disorders diagnosed by pharyngeal high-resolution manometry impedance (P-HRM-I). Methods Seventy-two patients (18-89 years) referred for P-HRM-I were diagnostically assessed with a 10 mL thin bolus. In 57 of the patients, 10 mL swallows of two moderately thick formulations-xanthan gum (XG) and sodium carboxymethylcellulose gum (CMC)-were also tested. The XG and CMC fluids had equivalent empirical thickness but different viscosity at pharyngeal phase shear rates: XG 87 mPa.s (83-91) versus CMC mean 157 mPa.s (148-164) at 300 s-1. Standard metrics of pharyngeal and upper esophageal sphincter (UES) function were derived from P-HRM-I recordings and analyzed to characterize patients into one of four disorder subtypes: (i) No Disorder, (ii) UES Disorder, (iii) Pharyngeal Disorder, and (iv) Combination UES/Pharyngeal Disorder. Impedance recordings also assessed pharyngeal bolus transit. Results Patients with a Combination UES/Pharyngeal Disorder were most likely to have abnormal bolus transit (82%, p < 0.001). Increasing bolus viscosity significantly influenced UES residual pressure, UES opening area, and post-swallow residue. Patients with UES Disorder exhibited pronounced increases in UES residual pressure with CMC compared to XG. Pharyngeal contractility was unaffected by viscosity changes. Post-swallow residue increased with CMC, particularly in patients with a Combination Disorder. Case-by-case analysis revealed individual variability in response to the different viscosities. Conclusion The rheological properties of thickened fluids significantly affect swallowing function, with these effects dependent upon the disorder subtype.