The effect of thickened carbonated liquids on oral and pharyngeal function during swallowing in older adults with dysphagia: a videofluoroscopic study

Older adults with dysphagia often exhibit reduced oral function—such as decreased tongue pressure and diminished oral sensation—that can impair bolus formation and clearance, increasing the risk of aspiration. Although thickened liquids are widely used to enhance swallowing safety, the combined effect of carbonation and thickening has not been fully evaluated via videofluoroscopic swallowing study (VFSS) in older patients with dysphagia. Therefore, this study evaluated the effects of thickened carbonated liquids on swallowing function in older adults with dysphagia using a VFSS to compare them with other liquid types, focusing on oral residue and the safety of bolus transfer from the oral cavity to the pharynx. In this prospective comparative study, 36 older adults (age 81.3 ± 9.5 years) with dysphagia (Modified Water Swallow Test score ≥ 4) underwent VFSS to compare four lemon-flavored liquids: thin liquid (Thin), thickened liquid (Thick), carbonated thin liquid (C-Thin), and carbonated thickened liquid (C-Thick). Oral-pharyngeal transit time, hypopharyngeal transit time, oral/pharyngeal residue, Penetration-Aspiration Scale (PAS), and subjective difficulty of swallowing (SDS) were measured. C-Thick significantly prolonged oral-pharyngeal transit time compared to Thin and Thick ( p < 0.05). Among participants with a baseline PAS score ≥ 2, C-Thick markedly reduced aspiration risk ( p < 0.01). Oral residue was higher for Thick than for C-Thin ( p < 0.01), whereas C-Thick promoted smoother passage and was particularly beneficial for severe dysphagia. No significant differences were found in hypopharyngeal transit time, vallecular/pyriform sinus residue, or SDS across liquids. These results indicate that the synergistic effects of carbonation and thickening—providing both sensory stimulation and bolus flow control—may improve swallowing safety and reduce oral residue in older patients with compromised oral function. Thickened carbonated liquids (C-Thick) represent a potential intervention for facilitating safer oral intake in older adults with dysphagia and age-related declines in oral function. By prolonging oral-pharyngeal transit time and enhancing oral bolus clearance, C-Thick can help mitigate aspiration risk, especially in patients at high risk. Future research should explore long-term effects, individualize carbonation and viscosity levels based on dental/oral health status, and evaluate outcomes in diverse dysphagia etiologies to establish comprehensive guidelines for clinical practice.