Figure 9 - Example of esophagopharyngeal acid regurgitation occurring during a transient UES relaxation, but aided by strain.

Note that although acid has been present in the esophagus for some time, the UES relaxes spontaneously. Less than 1 second later, aided by strain, which raises intraesophageal pressure, acid refluxes into the pharynx. {Ed: tUESR = transient upper esophageal sphincter relaxation; UES = upper esophageal relaxation}