Temporal Analysis of Swallowing Across IDDSI Liquid Thickness Levels in Young and Older Adults

This study examined thickness-dependent changes in temporal swallowing parameters across International Dysphagia Diet Standardisation Initiative (IDDSI) Levels 0–4 in healthy young and older adults using videofluoroscopic swallowing study (VFSS). In this cross-sectional study, 30 young adults (18–39 years) and 30 older adults (≥ 65 years) without swallowing or masticatory impairment completed VFSS with five barium-mixed liquid stimuli. Bolus transport measures (oral processing time, post-faucial aggregation time [PFAT], vallecular aggregation time [VAT], hypopharyngeal transit time [HTT]) and pharyngeal measures (swallow reaction time, time-to-laryngeal vestibule closure [LVC], LVC duration, hyoid burst to upper esophageal sphincter [UES] opening interval [HYB-UESO], UES opening duration) were assessed using definitions consistent with the ASPEKT Method (Analysis of Swallowing Physiology: Events, Kinematics and Timing). Within-group thickness effects were analyzed with Friedman and Wilcoxon signed-rank post-hoc tests; an Aligned Rank Transform (ART) ANOVA explored age-related differences. Increased bolus thickness significantly prolonged oral processing time and the HYB-UESO interval in both groups, with oral processing time longest at Level 4. In older adults, thicker consistencies additionally prolonged PFAT, VAT, and swallow reaction time, and shortened UES opening duration. Exploratory ART analyses showed a significant age × consistency interaction for oral processing time, VAT, and swallow reaction time. HTT and time-to-LVC did not differ significantly across thickness levels, and LVC duration was longer at Level 0 than at thicker consistencies in young adults only. These findings suggest thickness-dependent modulation of swallowing physiology, more extensive in older adults. Larger, adequately powered studies are needed to confirm these differences in dysphagic populations.