Reference Values for Healthy Swallowing Across the Range From Thin to Extremely Thick Liquids.

Only 40 people consented, and the final data set included 39 participants, with 38 full data and 1 partial data. All participants were healthy adults under 60 years, so the values do not describe older adults or people with swallowing disorders. Thin, slightly thick, and mildly thick liquids were taken as natural sips, while moderately and extremely thick liquids were taken by teaspoon, so sip size differed by consistency. Because sip size varied across consistencies, it is hard to separate the effect of liquid thickness from the effect of bolus volume. The consistencies were presented in a fixed order from thin to extremely thick, so order effects cannot be ruled out. Only xanthan gum thickened liquids were tested, so these values may not apply to liquids thickened with other products. Some data were missing or removed: one participant withdrew before videofluoroscopy, thin liquid data were lost for two participants, and one high sip-volume outlier was removed. Residue scores were heavily skewed, and some residue analyses were recoded into binary measures, so residue reference values are less straightforward than timing values. The data did not identify clear boundaries along the consistency continuum where specific swallowing changes can be expected. Timing was measured by frame counts, so very small differences between events can be hard to interpret.

Funding was provided by an RO1 grant from the National Institute on Deafness and Other Communication Disorders to the first author. The text does not report a commercial sponsor or author conflicts of interest.

Do not use these values to conclude that thickened liquids are safe for patients with dysphagia. The study included healthy adults under 60 years, not patients, and thicker liquids were delivered by teaspoon, so sip size was not the same across consistencies.