PMC

PRISMA flow diagram of the search process used in this systematic review

a Prevalence of penetration–aspiration by liquid bolus consistency, as reported in a study of stroke patients by Bingjie et al. []. Penetration–aspiration scale scores of 1 and 2 are considered normal; scores of 3–5 indicate penetration of the laryngeal vestibule, while scores of 6–8 indicate aspiration of material below the true vocal folds. b Differences in the severity of penetration–aspiration as a function of liquid bolus consistency, as reported in a study of patients with Parkinson’s disease by Troche et al. []