Effects of the internal syringe shape on the International Dysphagia Diet Standardization Initiative flow test

The International Dysphagia Diet Standardization Initiative (IDDSI) proposed the flow test (FT) as a simple method for measuring the viscosity of thickened liquids. However, the FT specifies the use of a particular syringe type (BD-Slip), which is unfortunately not easily available in Japan. Therefore, the current study primarily aimed to investigate the effects of the internal syringe shape on IDDSI FT and identify the most suitable syringe available in Japan for xanthan gum-based thickened liquids. Accordingly, four syringes, namely, Luer slip tip, Luer-Lok tip, TERUMO, and NIPRO syringes, were used to examine FT value with water and nine different water viscosity levels. The correlation and systematic errors on residual FT values between the BD-Slip syringe and the other three syringes were analyzed. The two-dimensional internal shapes of the four syringes were measured using industrial computed tomography (CT) scanning. Based on the results of our FT, TERUMO had the smallest error range among the three syringes, without systematic errors. On a CT scan, three of five tip-shape parameters showed the smallest difference between BD-Slip and TERUMO syringe. Therefore, TERUMO had the smallest FT error range compared with that in BD-Slip tip syringe, indicating that TERUMO could be used as a substitute for BD-Slip when performing IDDSI FT with xanthan gum-based thickened water in Japan.