Relationship between Flow Properties of Thickener Solutions and Their Velocity through the Pharynx Measured by the Ultrasonic Pulse Doppler Method

Abstract

The effect of viscosity µ of thickener solutions on their velocity through the human pharynx measured using the ultrasonic pulse Doppler method was investigated to develop an index for thickener solutions used as foods for dysphagic patients. The B-type viscometer determined an approximated value of viscosity at a selected shear rate γ · . The maximum velocity V max of water, which is often aspirated into trachea of patients with dysphagia, was about 3 times higher than that of yogurt, which is rarely aspirated. Moreover, the velocity spectra for water and thickener solutions of low concentration tended to be distributed over a wider range than those of yogurt and thickener solutions of high concentration. The maximum velocity V max of the thickener solutions approached that of yogurt as concentration increased. The maximum velocity V max correlated well with µ; the correlation coefficient at the shear rate of 10 s -1 was somewhat larger than those at the shear rate of 1 s -1 and 100 s -1 .

Determination of a Suitable Shear Rate for Thickened Liquids Easy for the Elderly to Swallow

“…However, the corresponding (average) value of a shear rate can be calculated with the B-type viscometer (Mitschka, 1982). Kumagai et al (2009) indicated that the viscosity measured with two types of viscometers, i.e., the B-type and cone-and-plate viscometers, coincided considerably well at the same shear rate. The B-type viscometer is widely used in Japan because it is cheaper than the cone-and-plate viscometer and is easy to operate.…”

“…It was determined that the relationship between the time during which the bolus front moved from the middle to the inferior pharynx and the viscosity of non-Newtonian fluids was approximate to that of Newtonian fluids, whose viscosities range from 10 to 1,000 mPa·s, if the non-Newtonian fluid viscosity was evaluated for the characteristic shear rate of 100 s -1 under a liquid bolus volume of 30 mL in a vertical direction. However, it was reported that 10 − 30 s -1 is the best shear rate (Kumagai et al, 2009;Tashiro et al, 2010a). As this was based on the evaluation of different regions, using 10 s -1 as reported by Kumagai et al (2009) in our study would mean that the rank order from low to high viscosity would be: No.…”

“…However, it was reported that 10 − 30 s -1 is the best shear rate (Kumagai et al, 2009;Tashiro et al, 2010a). As this was based on the evaluation of different regions, using 10 s -1 as reported by Kumagai et al (2009) in our study would mean that the rank order from low to high viscosity would be: No. 1; No.…”

“…This criterion indicates a lower limit of viscosity and states that the viscosity of soltype foods should be measured using a Brookfield-type viscometer, commonly known as the B-type viscometer, at a rotor rotation rate of 12 rpm at 20℃. This rotor rotation rate is calculated to an approximate shear rate of 2 − 3 s -1 (Kumagai et al, 2009). In 2009, FOSDU was changed to "Foods for the elderly with difficulty in swallowing," which denotes a new measuring standard for gel-type foods, but the sol-type foods criterion was excluded because there was insufficient evidence for the measuring method of sol-type foods in Japan.…”

“…This may not be the optimal method for measuring fluid viscosity; therefore, we aimed to determine the suitable shear rate for measuring TOROMI viscosity. In Japan, certain reports have discussed that the shear rate of 2 − 3 s -1 is too slow to evaluate viscosity and velocity through the pharynx (Kumagai et al, 2009;Tashiro et al, 2010a;Tashiro and Ono et al, 2010b). As the condition of shear rate changes with the evaluation of viscosity in the mouth, which would in turn depend on the viscosity of a liquid (Shama and Sherman, 1973), it appears that there are suitable shear rate ranges to measure viscosities that are easy to swallow in dysphagia.…”