A method for determining the characteristic shear rates of fluids in the pharynx is advanced here using videofluorography on three healthy subjects. Bolus velocity (V) was measured for five Newtonian fluids (using different concentrations of glucose syrup), with viscosities in the range of 0.0089-0.657 Pa·s, and was expressed as a function of viscosity (η). Shear thinning liquid food (with four different thickener concentrations) was also used where the apparent viscosities were adjusted to match the Newtonian fluid viscosities in the shear rate range of 10-1,000/s. The Newtonian and shear thinning liquid bolus velocities were both assumed to follow the same function V = F(η), which gave the shear thinning liquid characteristic viscosities ηc [=F −1 (V)]. Substituting ηc into the rheological model gave γ c , the characteristic shear rate dominating bolus flow at the pharynx. γ c values of 120 and 990/s were found at the meso-and hypopharynx, respectively, and these were approximately independent of ηc (and thickener concentration). V was found to be a function of both the characteristic viscosity and the differences between the individuals tested. PRACTICAL APPLICATIONSThe viscosity of liquid foods (e.g., in care homes) can be increased using a thickener, suppressing the effects of swallowing disorders. Thickened liquid food shows viscous shear thinning behavior, and the apparent viscosity depends on shear rate. When the viscosity of the food is adjusted for a patient with a swallowing disorder, the viscosity should be measured at the shear rate that dominates the liquid bolus flow at the pharynx. The measured viscosity is expected to correlate well with the bolus flow characteristics. The new experimental methodology proposed herein can be used to determine the characteristic shear rate at the pharynx.

Food bolus cohesiveness plays an important role to suppress miss-swallowing in swallowing disorder. The cohesiveness of masticated particles can be enhanced by binding liquids, which often represent high spinnability similarly as oral saliva does. Thus, in addition to shear viscosity, the extensional viscosity is important to control the bolus swallowing. Using a capillary thinning extensional viscometer, this study measured the extensional viscosity of natural okra, yam, and kelp mucilage in addition to whole saliva and a thickener solution for liquid care foods. The mucilages showed very high extensional viscosity, which was two or three orders of magnitude higher than the shear viscosity. The rheological characteristics for shear and extensional flow were found to be described by a Giesekus model approximately. The results obtained here can be applied to simulate the bolus swallowing numerically and to improve care foods for swallowing disorder.

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This paper reports a new microforce generating machine under development at NMIJ, AIST. We proposed a new microforce generating method by referring to the principle of the Kibble balance experiment and planned to apply it to a rotary type machine. Microforce in the micronewton and millinewton range can precisely be generated using this newly developed machine.

Herein, we report the development of a microforce-generating machine using electromagnetic force based on the principles of a Kibble balance to establish microforce traceability for ensuring the reliability of microforce measurements. We proposed a rotary-type microforce-generating machine using a combination of a balancing arm, a coil, and magnets. The microforce was generated through the balancing arm from the electromagnetic torque acting between the coil and magnets. The device eigenvalue, which served as the proportionality factor associated with the magnetic and geometric properties, was evaluated experimentally. The relationships between the eigenvalue and the temperature of the neodymium magnets, the rotation direction of the neodymium magnets, and the inclination of the balancing arm were discussed. The repeatability and reproducibility of the realized microforce were evaluated at force steps of 10 and 20 mN, and they were in the range of 3.8 × 10−5–3.9 × 10−4. We demonstrated that a microforce transducer could be calibrated using the proposed machine.