Purpose Thickened liquids are frequently used as an intervention for dysphagia, but gaps persist in our understanding of variations in swallowing behavior based on incremental thickening of liquids. The goal of this study was to establish reference values for measures of bolus flow and swallowing physiology in healthy adults across the continuum from thin to extremely thick liquids. Method A sex-balanced sample of 38 healthy adults underwent videofluoroscopy and swallowed 20% weight-to-volume concentration barium prepared in thin and slightly, mildly, moderately, and extremely thick consistencies using a xanthan gum thickener. Participants took comfortable sips and swallowed without a cue; sip volume was measured based on presip and postsip cup weights. A standard operating procedure (the ASPEKT method: Analysis of Swallowing Physiology: Events, Kinematics and Timing) was used to analyze videofluoroscopy recordings. Results The results clarify that, for thin liquid sips (10–14 ml), a single swallow without clearing swallows is typical and is characterized by complete laryngeal vestibule closure, complete pharyngeal constriction, and minimal postswallow residue. Aspiration was not seen, and penetration was extremely rare. Bolus position at swallow onset was variable, extending as low as the pyriform sinuses in 37% of cases. With thicker liquids, no changes in event sequencing, laryngeal vestibule closure, pharyngeal constriction, or postswallow residue were seen. The odds of penetration were significantly reduced. A longer timing interval until onset of the hyoid burst movement was seen, with an associated higher bolus position at swallow onset. Other timing measures remained unaffected by changes in bolus consistency. Conclusion The results include new reference data for swallowing in healthy adults across the range from thin to extremely thick liquids.

Purpose During swallowing, the tongue generates the primary propulsive forces that transport material through the oral cavity toward the pharynx. Previous literature suggests that higher tongue pressure amplitudes are generated for extremely thick liquids compared with thin liquids. The purpose of this study was to collect detailed information about the modulation of tongue pressure amplitude and timing across the range from thin to moderately thick liquids. Method Tongue pressure patterns were measured in 38 healthy adults (aged under 60 years) during swallowing with 4 levels of progressively thicker liquid consistency (International Dysphagia Diet Standardisation Initiative, Levels 0 = thin , 1 = slightly thick , 2 = mildly thick , and 3 = moderately thick ). Stimuli with matching gravity flow (measured using the International Dysphagia Diet Standardisation Initiative Flow Test; Cichero et al., 2017 ; Hanson, 2016 ) were prepared both with/without barium (20% weight per volume concentration) and thickened with starch and xanthan gum thickeners. Results After controlling for variations in sip volume, thicker liquids were found to elicit significantly higher amplitudes of peak tongue pressure and a pattern of higher (i.e., steeper) pressure rise and decay slopes (change in pressure per unit time). Explorations across stimuli with similar flow but prepared with different thickeners and with/without barium revealed very few differences in tongue pressure, with the exception of significantly higher pressure amplitudes and rise slopes for nonbarium, starch-thickened slightly and mildly thick liquids. Conclusions There was no evidence that the addition of barium led to systematic differences in tongue pressure parameters across liquids with closely matched gravity flow. Additionally, no significant differences in tongue pressure parameters were found across thickening agents. Supplemental Material https://doi.org/10.23641/asha.7616537

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