The overall objective of this protocol is to better understand normal and abnormal oral pressure dynamics and suprahyoid-infrahyoid muscle group coordination as a function of swallowing task. The specific goals are: (1) to determine if oral pressure properties differs during discrete vs. rapid sequential swallows in healthy adults of different ages; (2) to determine how oral maximum isometric pressure and task-specific swallowing pressure patterns differ between healthy adults and patients with reduced tongue strength and dysphagia; (3) to determine via surface electromyography (sEMG) if and how swallowing task affects suprahyoid and infrahyoid muscle activity coordination; (4) to determine the relationship between oral pressure patterns and videofluoroscopic signs of dysphagia in patients; and (5) to identify from the patients? oral pressure profiles indices for ability vs. inability to use rapid sequential swallowing as a compensatory strategy in dysphagia rehabilitation. To date we have studied 30 healthy volunteers and 6 patients with neurologic impairments. In 2003, our analysis focused on normal suprahyoid and infrahyoid muscle activity coordination. Our measurements included: max, mean, and ending amplitudes; start-to-max and max-to-end slopes; area under the curve; total sEMG activity duration; and suprahyoid-infrahyoid temporal differences in activity onset, offset, and time of max amplitude. Repeated measures ANOVAs were performed on the data of 107 rapid sequential and 106 discrete swallows with Bonferroni-Holm adjustment of alpha for the main effects and Tukey-Kramer adjustment of p for qualified post-hoc comparisons. Results showed no significant task-induced differences in suprahyoid-infrahyoid timing coordination measures. In addition, for all swallowing tasks, max amplitude was greater for suprahyoid than for infrahyoid sEMG responses (p < .0001). Rapid sequential swallows had steeper suprahyoid start-to-max slope, steeper infrahyoid max-to-end slope, higher suprahyoid and infrahyoid ending amplitude, and shorter suprahyoid and infrahyoid total sEMG activity duration than any discrete tasks (p < .0001 in each case). Subjects differed significantly across all variables assessed, especially for the rapid sequential swallowing task in max amplitude and area under the curve. At least for the rapid sequential swallowing task, our two oldest subjects (59.5 & 60.8 yrs in age) collectively differed considerably from the others in selected measures (e.g., lower max/mean amplitude and reduced slopes), suggesting a trend for age-related effects. While the muscles targeted by this study clearly showed a pattern of coactivation regardless of task nature, hooked wire EMG studies of hyolaryngeal depressors are needed to fully understand task-specific suprahyoid and infrahyoid neuromuscular coordination during swallowing. Our finding of greater suprahyoid than infrahyoid maximal amplitude suggests greater suprahyoid peak tension which, in turn, suggests recruitment of a greater number of motor units and greater amount of energy for the muscle complex that plays a leading role in swallow initiation. It remains unclear if our finding of partial suprahyoid and infrahyoid muscle relaxation during cyclical drinking reflects a passive by-product of shortened task execution time or an active motor control strategy. Only if the latter is proven true by our data in the future can we then interpret such finding within the context of motor economy and efficiency in the use of energy resources.
