Symptom hypersensitivity to acid infusion is associated with hypersensitivity of esophageal contractility

Several investigators have observed that repeated acid infusions induce stronger symptoms (symptom hypersensitivity). The goal of our study was to determine whether symptom hypersensitivity is associated with esophageal contractile hypersensitivity. Subjects with chronic heartburn symptoms underwent simultaneous pressure and ultrasound imaging of esophagus. Normal saline and 0.1 N HCl were sequentially infused into the esophagus, and subjects scored heartburn symptoms on a 1-10 scale. Saline and HCl infusions were repeated in 10 subjects with a positive Bernstein test. Esophageal contraction amplitude and duration and muscularis propria thickness were measured using a computerized method during recording. Acid infusion induced heartburn. Esophageal contractions had higher amplitudes (pressure 114.2 +/- 7.0%) and longer duration (116.8 +/- 4.4%) during acid infusion compared with saline infusion. Average muscle thickness was greater during acid infusion than saline infusion (107.0 +/- 2.0%). Sustained esophageal contractions (SECs) were identified during acid infusion. A second acid infusion (acid-2) induced heartburn with shorter latency (93.0 +/- 15.0 vs. 317.0 +/- 43.0 s) and stronger severity (8.5 +/- 0.5 vs. 5.3 +/- 0.8) than the first acid infusion (acid-1). Contraction amplitudes (140.2 +/- 13.0%), average muscle thickness (118.0 +/- 3.3%), and contraction duration (148.5 +/- 5.6 vs. 116.8 +/- 4.4%) were higher during acid-2 than acid-1. Also, numbers of SECs were greater during acid-2 than acid-1 (31 in 8 subjects vs. 11 in 6 subjects). Our data show that acid infusion into esophagus induces esophageal hypersensitivity and that a close temporal correlation exists between symptom hypersensitivity and contractility hypersensitivity.