Activity pattern of swallowing-related muscles, food properties and body position in normal humans

Activity patterns of the swallowing-related muscles were examined in normal subjects at different four body positions during swallowing of foods with different textural properties. Surface electromyograms were recorded from two muscle groups, the anterior tongue and suprahyoid muscles. The T(P) technique we developed was applied to the electromyograms for quantitative analysis of the activity patterns. Three test foods were prepared by dissolving 2.0% (low), 5.7% (middle) and 9.1% (high concentration) of a thickening agent into distilled water. Each subject was delivered randomly, one of the test foods to swallow at one of the four body positions i.e. horizontal supine, 30 degrees inclined, 60 degrees inclined and upright. In this study, T(50) values were calculated in activity data of the two muscle groups, and the T(50) values were statistically examined analysis of variance with a linear model including four fixed effects of 'concentrations', 'body positions', 'subjects' and 'sessions'. Three major findings obtained were that (i) the activity pattern of the anterior tongue was altered from a decrementing discharge pattern to an incrementing discharge pattern by shifting from the upright to the horizontal supine position, (ii) the activity pattern of the suprahyoid muscles was altered from a decrementing discharge pattern to an incrementing discharge pattern by shifting from the low concentration food to the higher ones and (iii) two subgroups were detected in subjects with the significant effects of 'concentrations' and 'body positions'. These findings lead a conclusion that activity patterns of the swallowing-related muscles are affected by food properties and body positions.