Experimental and Computational Investigation of the IDDSI Flow Test of Liquids Used in Dysphagia Management

Abstract

The International Dysphagia Diet Standardisation Initiative (IDDSI) flow test, using a standard 10-mL syringe, is being adopted in many countries for clinical measurement of the consistency of drinks. The working hypothesis is that thickening drinks to retard flow can be advantageous for individuals who struggle to cope with thin drinks. This study assesses how the IDDSI test relates to rheology and clinical knowledge of physiological flows during swallowing. With no pre-existing analytical solution for internal flow through the syringe, a computational model was designed, incorporating rheometry data from a variety of Newtonian and non-Newtonian liquids. The computational model was validated experimentally across the range of liquids but the technique showed limitations in simulating dripping and cohesiveness. Gum-based liquids which were strongly shear-thinning (0.12 < n < 0.25) showed plug-flow characteristics with 90% of the shear occurring in only 22% of the radial dimension. Shear rates were maximal at the nozzle outlet (> 60 times higher than the barrel) and reached 7400/s for the thinnest gum-based liquid. Shear rheology data alone was unable to describe the flow of these drinks. The flow conditions in the test varied according to the type and consistency of liquid, relating to the desired clinical effect.

Is IDDSI an Evidence-Based Framework? A Relevant Question for the Frail Older Population

“…The IDDSI flow test was compared to other empirical methods (line-spread test and Bostwick consistometer) as well as rheological methods (viscometer and rheometer) to categorize various liquids. These methods showed that characterization of liquids tested could be similar, but not identical [ 43 , 45 , 46 , 47 , 50 , 55 , 60 ]. Measures of IDDSI flow test may vary depending on the type of thickening agent (starch versus gum) and the liquid used, even though some rheological parameters such as viscosity are similar [ 43 , 45 , 47 ].…”

“…These methods showed that characterization of liquids tested could be similar, but not identical [ 43 , 45 , 46 , 47 , 50 , 55 , 60 ]. Measures of IDDSI flow test may vary depending on the type of thickening agent (starch versus gum) and the liquid used, even though some rheological parameters such as viscosity are similar [ 43 , 45 , 47 ]. Thus, two liquids of the same level IDDSI may have different viscosities or different flows when measured with another method [ 43 , 45 , 46 , 60 ].…”

Liquids offered in pediatric videofluoroscopy swallowing study: A preliminary rheological analysis

“…(Sukkar et al., 2018) Actually, a recent study sought to overcome this challenge. (Hanson, Jamshidi, Redfearn, Begley, & Steele, 2019).…”

Texture-Modified Food for Dysphagic Patients: A Comprehensive Review

“…This test classifies consistency based on the volume of the residual liquid in the syringe after a period of a 10 s flow. The resulting levels are then defined as level 0 thin (0–1 mL liquid remaining), level 1 slightly-thick (1–4 mL), level 2 mildly thick (4–8 mL) and level 3, moderately thick (8–10 mL) [ 48 ]. The new International Dysphagia Diet Standardization Initiative (IDDSI) classification system considers practical measurements for liquids that could be used in kitchens, bedsides and in laboratories.…”