Development of a simple evaluation instrument for liquid thickness measurement.

Simple methods, such as the line spread test (LST), are often used to evaluate thickened liquids in clinical settings. Although it is desirable for these simple methods to be rapid, even the LST requires approximately 1 min to complete the evaluation. Herein, we aimed to shorten this time by developing a new simple instrument for evaluating thickened liquids considering the fluid engineering perspective with improved funnel design and evaluation methods. A thickened liquid was prepared with a xanthan gum-based thickening agent and water. Samples with viscosities of approximately 50, 150, 300, and 500 mPa∙s were prepared. For evaluation, 30 ml of the sample was injected manually with the outlet closed. The outlet was then opened to allow the liquid to fall as soon as the evaluation began. The time taken for the water surface of the liquid to move 50 mm from the starting point to the target point was measured eight times using a stopwatch, and the average was taken as the evaluation time. The instrument took 2.22-3.29 s, 3.29-9.16 s, and 9.16-23.14 s to classify mildly thick, moderately thick, and extremely thick samples, respectively. This method enabled extremely thick samples to be evaluated in 23 s, which is 27 s less than the time taken by the conventional funnel method. Verification results showed that this developed evaluation instrument for thickened liquids could perform classification according to the criteria of the Japanese Dysphagia Diet 2013. We aim to improve its design for clinical use in the future.