A Systematic Review of Reported Methods of Stimulating Swallowing Function and their Classification

Recent advances in dysphagia treatment have given us many methods of stimulating swallowing function, but no attempt has been made to systematically classify them all. In this review, we provide an exhaustive description of all the techniques and stimulatory substances that stimulate swallowing that have so far been reported in the scientific literature, irrespective of their level of evidence, and we have tried to classify them with the objective of encouraging the future development of research in this direction. The Preferred Reporting Items for Systematic Reviews and Meta-analysis were followed for retrieval of relevant research. A total of 237 records were screened for this literature review. One record was excluded for being published in a language other than English, and 59 articles were excluded for having no original data. Of the 177 records that were assessed for eligibility in this review, 31 were excluded for reasons related to other inclusion and exclusion criteria. Finally, 146 records were classified. We found stimuli related to swallowing published in the literature could be divided into physical and chemical stimuli. Each stimulus had both peripheral and central stimuli when we assessed the main site of action. Physical stimuli included electric, magnetic and thermal stimulations and acupuncture. Chemical stimuli included spices activating transient receptor potential channels, several categories of medications, taste and flavor, and olfactory stimulants. Medications modifying substance P and the dopaminergic system are thought to be peripheral and central stimuli, respectively. This classification may pave the way to discover means to improve swallowing.