Relationship between swallow rate and salivary flow

Abstract

Recent studies indicate that swallow-induced, primary peristalsis is a major determinant of normal esophageal acid clearance. However, factors that regulate the rate of spontaneous swallowing in normal subjects are incompletely understood. We postulated that the rate of salivary flow influences the rate of spontaneous swallows. To test this hypothesis, we did a total of 60 studies measuring salivary flow or the rate of spontaneous swallowing in 10 healthy volunteers, age 10-30 years. Saliva was collected by expectoration. Swallow rate was recorded by a small, transnasal catheter stationed in the pharynx and also, in some circumstances, by cervical electrodes. On separate sessions, we evaluated the effect of five test manipulations on salivary flow and swallowing rate, respectively. The test manipulations consisted of: (1) pharyngeal intubation, (2) sucking of a dummy lozenge, (3) sucking of a peppermint lozenge, (4) bethanechol injection (5 mg subcutaneously), and atropine administration (12 micrograms/kg intravenously). Pharyngeal intubation caused a small, but significant increase in the rate of salivation and spontaneous swallows. Sucking of a peppermint lozenge caused a sixfold increase in salivary flow while nearly doubling the swallowing rate whereas the dummy lozenge caused only a modest increase in salivary flow and swallowing. Cholinergic stimulation by bethanechol elicited a substantial increase in salivary flow and swallowing rate. In contrast, atropine caused a significant decrease in both salivary flow and swallowing. We conclude that in awake, normal subjects the rate of spontaneous swallows is influenced directly by salivary flow. Because oral lozenges substantially increase both swallowing rate and salivary flow, such agents merit investigation as a potentially useful ancillary treatment for the relief of heartburn.