The tongue enacts complex mechanical events during swallowing, the most important of which is the propulsion of a bolus from the oral cavity to the pharynx. Successful bolus transport requires the tongue to interact with other oral structures, especially the hard palate, to generate sufficient impulsive force or pressure gradients that drive the bolus toward the oropharynx. Our knowledge of deglutitive lingual pressure dynamics is at best incomplete. The available data on oral tongue pressure phenomena are based exclusively on commanded single swallows. Oral pressure changes during other important everyday eating activities (e.g., cup drinking) have not been studied to date. Past investigations revealed that rapid sequential swallowing during continuous drinking, in contrast to commanded discrete swallows, had unique tongue-palate contact patterns, surface electromyographic response characteristics, and hyoid displacement profiles. Given the different biomechanical properties and motor strategies, we hypothesize that oral lingual pressure profiles for sequential swallowing are also different, that sequential swallows require less impulsive force, and that selected dysphagic patients, especially those whose swallowing deficits are associated with reduced tongue strength, will perform sequential swallows more efficiently than they do discrete swallows. This protocol, therefore, proposes to test these hypotheses in healthy individuals of different ages, and in patients with reduced tongue strength and oral/oropharyngeal dysphagia associated with neurologic disorders, musculoskeletal diseases, or head and neck cancer. Our goals are to: (a) acquire a better and more complete understanding of normal tongue pressure phenomena as a function of swallowing tasks, (b) characterize the interrelationship between task-induced lingual pressure differences and results of clinical diagnostic tests of swallowing function in patient populations, and (c) differentially identify the profiles of dysphagic patients who can and those who cannot benefit from sequential swallowing as a compensatory/rehabilitative strategy. We completed the collection of normative data during this report period. To date, we have studied the oral pressure as well as suprahyoid and infrahyoid surface EMG (sEMG) profiles of 80 healthy volunteers and 5 patients as a function of discrete and rapid sequential swallowing tasks. In the area of oral pressure dynamics, our measurements include: pressure bulb activation duration, peak pressure distribution ratios, peak mmHg, start-to-peak and peak-to-end slopes, and area under the curve. In the area of temporal coordination and response characteristics of suprahyoid and infrahyoid muscle activities, our measurements include: 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. The focus of our current efforts is on data analysis. All data reduction has been completed. We expect to conclude statistical analyses, result interpretation, and the preparation of manuscript(s) within three months. Out past findings of significant effects of swallowing task (rapid sequential vs. discrete), regional specificity in lingual pressure generation (posterior vs. anterior), as well as a predominantly co-activation pattern of suprahyoid-infrahyoid motor coordination are expected to persist.
