The Impact of Bolus Rheology on Physiological Swallowing Parameters Derived by Pharyngeal High-Resolution Manometry Impedance.

BACKGROUND

The shear rheology of ingested fluids influences their pharyngo-esophageal transit during deglutition. Thus, swallowed fluids elicit differing physiological responses due to their shear-thinning profile.

METHODS

Two hydrocolloid fluids, xanthan gum (XG) and sodium carboxymethylcellulose gum (CMC), were compared in 10 healthy adults (mean age 39 years). Manometry swallowing assessments were performed using an 8-French catheter. Swallows were analyzed using the Swallow Gateway web application (www.swallowgateway.com). Grouped data were analyzed by a mixed statistical model. The coefficient of determination (r2) assessed the relationship between measures and bolus viscosity (SI units, mPa.s) at shear rates of 1-1000 s-1.

KEY

RESULTS

Rheology confirmed that the thickened fluids had similar viscosities at 50 s-1 shear rate (XG IDDSI Level-1, 2, and 3 respectively, 74.3, 161.2, and 399.6 mPa.s vs. CMC Level-1, 2, and 3 respectively 78.0, 176.5, and 429.2 mPa.s). However, at 300 s-1 shear, CMC-thickened fluids exhibited approximately double the viscosity (XG Level-1, 2, and 3 respectively 19.5, 34.4, and 84.8 mPa.s vs. CMC Level-1, 2, and 3 respectively, 41.3, 80.8, and 160.2 mPa.s). In vivo swallows of CMC, when compared to XG, showed evidence of greater flow resistance, such as increased intrabolus pressure (p < 0.01) and UES Integrated Relaxation Pressure (UESIRP, p < 0.01) and shorter UES Relaxation Time (p < 0.05) and Bolus Presence Time (p < 0.001). The apparent fluid viscosity (mPa.s) correlated most significantly with increasing UESIRP (r2 0.69 at 50 s-1 and r2 0.97 at 300 s-1, p < 0.05).

CONCLUSION

Fluids with divergent shear viscosities demonstrated differences in pharyngeal function. These physiological responses were linked to the shear viscosity and not the IDDSI level.