Effects of pharyngeal water stimulation on swallowing behaviors in healthy humans

The aims of the present study were to determine whether the interval between swallows and the electromyographic (EMG) burst patterns of the suprahyoid muscles is affected by peripheral inputs during swallowing. Eighteen normal adults were asked to perform repetitive voluntary swallowing as quickly as possible, and three variables of swallowing were measured and evaluated, i.e., the swallowing intervals and the time interval between the onset and peak (rising time) and between the peak and offset (falling time) of the suprahyoid EMG burst. During recording, pharyngeal fluid infusion was applied with distilled water or 0.3 M NaCl solution at a very slow infusion rate (0.2 mL/min). The former and latter were used to activate and inhibit the excitation of water-sensitive receptors in the pharynx, respectively. The swallowing interval was significantly shorter during infusion of water than during infusion of NaCl solution. The rising time was also significantly shorter during infusion of water than during infusion of NaCl solution. There was a linear positive correlation between these values and facilitatory effects: the longer either the swallowing interval or rising time with infusion of 0.3 M NaCl solution, the stronger the facilitation of swallowing by the activation of water receptors. Facilitatory effects on the swallowing interval and rising time showed a linear correlation. It is suggested that weak liquid stimulation changed sensory inputs into the swallowing center and synchronously modulated the swallowing interval and time interval between the onset and peak of the EMG burst.