Fluid thickening is a valid therapeutic strategy for patients with oropharyngeal dysphagia (OD). The main aim of this study was to determine the therapeutic effect of the xanthan-gum-based thickener Tsururinko Quickly (TQ, Morinaga Milk Co., Tokyo, Japan) in older patients with severe OD. A total of 85 patients (83.32 ± 6.75 y) with OD and a penetration–aspiration score (PAS) of n ≥ 3 were studied by videofluoroscopy while swallowing duplicate 10 mL boluses at <50 mPa·s, 100, 200, 400, 800, and 1600 mPa·s, to assess the safety and efficacy of swallowing and the biomechanics of a swallowing response at each viscosity level. At <50 mPa·s, only 16.25% patients swallowed safely, 45% had penetrations (PAS 3–5), and 38.75% had aspirations (PAS 6–8). Fluid thickening with TQ greatly increased the prevalence of patients with safe swallowing from 62.90% at 100 mPa·s to 95.24% at 1600 mPa·s in a shear-viscosity-dependent manner. The penetrations and aspirations were significantly reduced to 3.60% and 1.19%, respectively, at 1600 mPa·s. The threshold viscosity was 100 mPa·s and the increasing viscosity above 800 mPa·s did not further improve the therapeutic effect significantly. Increasing the shear viscosity significantly reduced the time to laryngeal vestibule closure (−16.70%), increased the time to upper oesophageal sphincter opening (+26.88%), and reduced the pharyngeal bolus velocity (−31.62%) without affecting the pharyngeal residue. TQ has a strong shear-viscosity-dependent effect on the safety of swallowing in older patients with severe OD without increasing the pharyngeal residue. The therapeutic range for TQ is 100–800 mPa·s, with 200 and 800 mPa·s being the optimal doses to cover the needs of older patients with OD.

Increasing shear viscosity (ShV) in thickening products (TP) is a valid therapeutic strategy for oropharyngeal dysphagia (OD). However, salivary amylase in the oral phase and shear rate in the pharyngeal phase of swallowing can change the viscosity of TPs when swallowed. This study aims to design and validate a rheological protocol to reproduce the oral and pharyngeal factors that affect the therapeutic effect of TPs and report the viscosity measurements in a standardized scientific and precise manner. We measured (a) the variability of the ShV measurements across several laboratories; (b) the in vitro and ex vivo properties of TPs and (c) the impact of the X-ray contrast Omnipaque, temperature and resting time on the rheological properties of TPs. A common protocol was applied in four international laboratories to assess five ShV values (100, 200, 400, 800 and 1600 mPa·s) for the xanthan-gum TP Tsururinko Quickly (TQ). The protocol included the dose (g/100 mL water), stirring procedure and standing time before measurement. Each value was characterized at the shear rate of 50 and 300 s⁻¹ pre- and post-oral incubation in eight volunteers. The effect of temperature, standing time and Omnipaque was assessed. The main results of the study were: (a) The mean intra-laboratory variability on the ShV at all levels was very low: 0.85%. The mean inter-laboratory variability was higher: 9.3%; (b) The shear thinning of TQ at 300 s⁻¹ was 75–80%. Increasing the temperature or standing time did not affect the ShV, and oral amylase caused a small decrease; (c) Omnipaque slightly decreased the dose of TP and hardly affected the amylase resistance or shear thinning. This study showed that different laboratories can obtain very accurate and similar ShV measurements using this protocol which uses scientific, universal SI units (mPa·s). Our protocol accurately reproduces oral and pharyngeal factors affecting the therapeutic effect of TPs. The addition of X-ray contrast did not produce significant changes.

To examine the relationship between pharyngeal residue and both the oral and pharyngeal stages by observing tongue pressure and pharyngeal dynamics during the swallowing of thickened liquid prepared with starch-based, guar gum-based, and xanthan gum-based thickeners. The participants were 20 volunteers without dysphagia (17 male, 3 female, 33.1 ± 8.8 years). Samples were water and liquids thickened with starch-based, guar gum-based, and xanthan gum-based thickeners, and each was 15 mL. The shear viscosity of thickened liquids was 400 mPa·s at 50 s-1. Whiteout duration and pharyngeal residue were observed by videoendoscopy, and swallowing sounds were recorded with a microphone. Tongue pressure was measured by using a multichannel sensor sheet placed on the palate. Whiteout duration, swallowing sound duration, and tongue pressure parameters were compared between the samples and the presence of pharyngeal residue. The frequency of pharyngeal residue was significantly higher with starch-based samples than with water and xanthan-based samples (P < 0.05). The swallowing sound duration was significantly shorter for all of the thickened samples compared with water (P < 0.05). The tongue pressure at the posterior-circumferential for starch-based and guar gum-based samples was found to be significantly different from that for water (P < 0.05). Furthermore, when pharyngeal residue occurred, tongue pressure was significantly greater (P < 0.01), and the whiteout duration and swallowing sound duration were significantly longer (P < 0.05, P < 0.01, respectively). Our findings suggest that the type of thickener influences both the oral and pharyngeal stages, which are associated with the occurrence of pharyngeal residue.

Xanthan gum-based thickeners are commonly used to treat dysphagic patients. Their rheological properties, such as shear-thinning, extension, and thixotropy, contribute to swallowing safety. However, the influence of rheological variations on swallowing dynamics remains unclear. This study investigated the impact of variations in the rheological properties of xanthan gum-based thickeners on swallowing dynamics, specifically tongue pressure, suprahyoid muscle activity, and swallowing sounds. Shear rheology, extensional viscosity, and 3-interval thixotropy tests were conducted on three commercial thickener solutions standardized to a 400 mPa·s viscosity at a 50 s⁻¹ shear rate. Twenty healthy volunteers (11 females, 24.6 ± 2.4 years) participated in this study, during which tongue pressure, suprahyoid muscle activity, and swallowing sounds were measured while swallowing 15 mL samples. The first thickener exhibited reduced shear viscosity at 300 s⁻¹, higher thixotropy, and shorter swallowing sound duration, suggesting a shortened pharyngeal transit time. The second showed prolonged filament breakage time and higher tongue pressure in the posterior-median region of the palate, leading to increased tongue activity during swallowing. The third exhibited lower extensional viscosity, different muscle activity than the second, and longer duration of swallowing sound than the first. These results suggest that rheological property variations in xanthan gum-based thickeners influence swallowing dynamics in healthy individuals.