The Effect of Carbonated Liquid on Swallowing Safety of People with Parkinson Disease (DYSparkLE): A Prospective Within-Subject, Repeated-Measures Observational Study

Impaired swallowing safety with thin liquids is a concern in patients with Parkinson disease (PwPD). Sensory stimulation is frequently used in dysphagia rehabilitation. Previous studies suggest that carbonated liquid (CL) has beneficial effects on swallowing function. The objective of this study is to evaluate how drinking CL influences swallowing safety in PwPD. PwPD were consecutively recruited at our Parkinson day-clinic from July 2023 to July 2024. Patients with atypical or secondary Parkinsonism and other neurological or oncological diseases also causing dysphagia were excluded. Swallowing was assessed using flexible-endoscopic evaluation of swallowing (FEES). The assessment protocol included 5 and 90 mL of unflavored non-carbonated liquid (nCL) and CL. The primary outcome was the depth of airway invasion (DAI) with 90 mL. 83 PwPD (25 women) were included (age: 67.8±9.4 years; UPDRS III (Unified Parkinson's Disease Rating Scale, Part III): 34.9±14.3 points; disease duration: 7.9±5.9 years). Multilevel logistic regression showed that with CL, the odds of an airway invasion are significantly reduced compared to nCL. A second, exploratory subgroup analysis using binary logistic regression showed that the odds for PwPD to benefit from CL are higher for those reporting fewer dysphagia symptoms. It also indicated a potential effect of impaired laryngeal sensitivity, which was associated with decreased odds of improvement with CL. With CL, significantly fewer unsafe swallows were observed in PwPD. Incorporating CL in instrumental assessment protocols allows individualized assessment of its effects. Future research should look at mechanisms underlying the impact of CL in this patient group and explore the value of CL in addition to dysphagia rehabilitation strategies.