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 .

Velocity spectrum of swallowed food particles in the pharynx were measured by the ultrasonic pulse Doppler method. Water, yogurt, jelly of gelatin and gellan of which concentration was changed were tested. The velocity distribution that passed just above the epiglottis of the pharynx was obtained. The velocity spectrum of water that dysphagia patients often aspirate to the trachea was compared with that of yogurt which rarely aspirated by them. The average velocity of all food samples tested was almost *.+ m/s ; the maximum velocity of water was *./ m/s and that of yogurt was *., m/s. In other words, velocity distribution of water particles was fairly wide compared with that of yogurt ; this would make di$cult for dysphagia patients to swallow water and relatively easy to swallow yogurt. Velocity spectra of thin sols were similar to that of water, but the maximum velocity was smaller as concentration of jelly increased. Dynamic viscoelasticity was measured and the relation to the maximum velocity measured by the ultrasonic method was examined. The maximum velocity of gels whose storage modulus was +** Pa or more, or viscosity was , Pa • s or more was almost *., m/s similar to that of yogurt. These results showed that risk of aspiration to the trachea of foods was inferred from dynamic viscoelasticity.

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