Objectives. To critically appraise scientific, peer-reviewed articles, published in the past 10 years on the effects of different levels of hydration on voice quality in adults. Study design. Systematic review. Method. Five databases were searched using the key words “vocal fold hydration/dehydration”, “voice quality”, “and “hygienic voice therapy”. The PRISMA-P guidelines were followed. The included studies were scored based on ASHA’s levels of evidence and quality indicators, as well as, the Cochrane Collaboration’s risk of bias tool. Results. Systemic dehydration as a result of fasting and not ingesting fluids had a significant, negative effect on the parameters of NHR, shimmer, jitter, frequency and the s/z ratio. Water ingestion led to significant improvements in shimmer, jitter, frequency and MPT values. Caffeine does not appear to negatively affect voice production. Laryngeal desiccation challenges by oral breathing led to surface dehydration which negatively affected jitter, shimmer, NHR, PTP and PPE. Steam inhalation significantly improved NHR, shimmer and jitter. Only nebulization of sterile water, isotonic solution and saline solution improved PTP, throat and mouth dryness and fundamental frequency respectively. An indication of a potential positive effect of nebulization substances was observed. Treatments in high humidity environments prove to be effective and adaptations of low humidity environments should be encouraged. Conclusion. Recent literature regarding vocal hydration is high quality evidence. Systemic hydration is the easiest and most cost effective solution to improve voice quality. Surface hydration using steam inhalation and nebulization as well as environmental modification can be suggested for professional voice users. Recent evidence therefore supports the inclusion of hydration in a vocal hygiene program.
Dissertation (MCommunication Pathology)--University of Pretoria, 2018.