The Effect of Bolus Viscosity and Dysphagia Severity on Laryngeal Closure During Swallowing in Patients with Post-Stroke Dysphagia: A Kinematic Analysis Using Swallowing CT

Previous research in healthy individuals has demonstrated that fast bolus progression of thin liquid results in earlier true vocal fold (TVF) closure compared to thick liquid. This study investigated whether this timing adjustment occurred in individuals with stroke and whether dysphagia severity affected this adjustment. This retrospective observational study included 54 participants with stroke (37 males, 17 females, mean [standard deviation] age: 63.7 [13.8] years) who underwent CT swallow studies with thick and thin liquids (10 ml each). The onset of TVF closure, laryngeal vestibule (LV) closure, maximum epiglottic inversion, and bolus head progression were compared between 2 consistencies. Subgroup analysis was based on the Dysphagia Severity Scale (DSS). The results showed that thin liquid reached the vallecula, hypopharynx, and esophagus significantly earlier than thick liquid. Onset of TVF closure was significantly earlier with thin liquid (median: 0.2 s [range: -1.5 to 0.5] vs. 0.3 s [range: -1.7 to 0.6], p = 0.020) with no significant differences in onset of LV closure or maximum epiglottic inversion. Subgroup analysis revealed significantly earlier TVF and LV closure with thin liquid only in the mild (DSS 5 and 6) group. Patients with moderate (DSS 4) and moderately severe (DSS 3) dysphagia did not show these differences. In conclusion, TVF and LV closure occurred earlier in response to faster bolus transport in stroke patients. However, this finding varied by dysphagia severity and was absent in the groups with more severe dysphagia. These data support the idea that TVF and LV adjustments are important factors in airway protection.