Observational study of effects of pharyngeal stimulation by carbonated solution on repetitive voluntary swallowing in humans

In this study, we conducted observational study to examine the effects of pharyngeal stimulation by a bolus of carbonated solution on repetitive voluntary swallowing in humans. Twelve healthy participants had a fine silicone tube inserted into their pharyngeal region, through which various solutions were slowly infused (0.2 mL/minute) to stimulate the pharyngeal mucosa without activating mechanoreceptors. The solutions included 0.3M NaCl (NaCl), carbonated 0.3M NaCl (NaCl + CA), 0.3M NaCl with acetic acid, distilled water, and carbonated distilled water. We used NaCl to inhibit water-sensitive neurons in the pharyngeal mucosa and enable the evaluation of the effects of carbonic acid stimulation on swallowing. Participants were instructed to repeat swallows as rapidly as possible during the infusion, and the swallowing interval (SI) was measured via submental surface electromyographic activity. SI was significantly shorter during the infusion of NaCl + CA, distilled water, and carbonated distilled water than during the infusion of NaCl. There was a significant positive correlation between SI with NaCl stimulation and the facilitative effects of the other solutions. Longer SIs with NaCl stimulation indicated potent facilitative effects. Thus, stimulation with NaCl + CA facilitated swallowing by reducing SI. Furthermore, the facilitative effects of SI were more pronounced in participants who had difficulty with repetitive voluntary swallowing. The sensation induced by carbonated solution may enhance the ability for repetitive voluntary swallowing, making it a potentially useful approach for rehabilitating patients with dysphagia.