When eating food containing both liquid and solid phases (two-phase food), the liquid component frequently enters the hypopharynx before swallowing, which may increase the risk of aspiration. The aim of this study was to test whether the initial viscosity of two-phase food would alter pre-swallow food transport and breathing-swallowing coordination in elderly persons. Fiberoptic endoscopy was recorded while 18 healthy young and 19 elderly subjects ate 5 g of steamed rice with 3 ml of blue-dye water. Liquid viscosity was set at three levels by adding a thickening agent (0, 2, and 4 wt%, respectively). We measured the timing of swallow initiation and the respiratory phase at swallow initiation. For thin twophase food, the timing of swallow initiation was not significantly different between young and elderly subjects, but swallows more initiated during inspiration in elderly subjects. For thicker two-phase foods, in contrast, the timing of swallow initiation was delayed in elderly subjects, but swallows usually initiated during expiration in both groups. In elderly individuals, for thin two-phase, swallow initiation is reserved but breathing swallowing coupling was declined. For higher viscosities, swallow initiation is delayed during eating food, but breathing swallowing coordination is not perturbed probably due to slow bolus flow into the hypopharynx. Coordination between swallowing and breathing pattern during eating of food would decrease with aging, which may expose a risk of pre-swallow aspiration.2015博士（臨床歯学）松本歯科大
