Relation between Bolus Size and Hyoid Movement during Normal Ingestion in Humans

Hyoid action was studied regarding bolus movement during normal ingestion in five subjects using videofluorography in the sagittal plane. The subjects were asked to take one mouthful of steamed rice and chew it normally until the mouth was empty. Food intake, transport to the postcanines, chewing, and swallowing were identified using frame-by-frame analysis of the images. Two types of swallowing were identified during the sequence: interposed and terminal swallowing. The former was observed during chewing, while the latter was observed at the end of the sequence. Differences were observed in the size of the food bolus passing through the pharyngo-esophageal junction: a larger volume was observed for the interposed swallow, which was reflected in the dilation of the junction and a longer time taken for the passage of food. There was no difference in hyoid movement between the two swallows, either in the vertical or horizontal direction, i. e., the hyoid moved maximally during its function in swallowing, regardless of the bolus size passing through the pharyngo-esophageal junction. This suggests that the swallowing-related motor action involved in hyoid movement is unaffected by sensory input.