The effects of swallowing frequency and transdermal scopolamine on esophageal acid clearance.

Fourteen volunteers were studied on two occasions to assess the effect of swallowing frequency on acid clearance time. The experimental protocol consisted of two trials of infusion of 15 ml of 0.1 N HCl into the distal esophagus. One trial required swallowing every 30 s for 10 min. The other trial involved an initial rapid swallowing rate (seven swallows in the 1st min) with a gradual predetermined decline in rate. This procedure was repeated 12 h after application of a transdermal scopolamine patch. Baseline clearance times for rapid and slow swallowing were not significantly different. The anticholinergic drug significantly prolonged the clearance times for both rapid and slow swallowing. Under baseline conditions, sequential swallows (after the first three to four swallows) produced a significant rise in pH until the clearance criterion of pH 4.0 was reached. This effect was abolished with the anticholinergic drug. These results support a two-stage model of acid clearance with initial volume clearance and subsequent salivary buffering of residual intraesophageal acid.