Effects of systematic bolus viscosity and volume changes on hyoid movement kinematics.

Using ultrasonography with head and transducer stabilization, this study examined the effects of maximally controlled, systematic changes in bolus viscosity (thin juice-like, 7 cP; nectar-like, 243-260 cP; honey-like, 724-759 cP; spoon-thick, 2760-2819 cP) and volume (5, 10, 20, 30 cc) on hyoid kinematics in 31 healthy subjects (16 male, 15 female) in three age groups (20-39, 40-59, 60-79 years). Frame-by-frame hyoid displacements were tracked from digitized images of 612 swallows. Measures of movement durations, maximal amplitudes, total distances, and peak velocities were subjected to repeated measures multivariate analyses of variance with viscosity, volume, age, and gender as factors. Results showed that (1) spoon-thick swallows had the greatest preswallow gesture and total movement durations; (2) larger-volume swallows had significantly greater maximal amplitudes, forward peak velocity, and total vertical distance; (3) older subjects had longer start-to-max duration (though shorter preswallow gesture and total movement durations), greater maximal vertical amplitude, longer total vertical distance, and greater backward peak velocity than younger subjects; (4) males had greater values for all kinematic parameters except preswallow gesture, hyoid-at-max, and max-to-end durations. The results illustrate the importance of examining the interrelations among kinematic variables to better understand task accommodation and motor control strategies. The evidence also supports the concept of suprahyoid-infrahyoid functional adaptation and compensation in the healthy elderly.