Normal patterns of acid exposure at the gastric cardia: A functional midpoint between the esophagus and stomach

Objective: Little is known about the normal anatomical patterns of acid exposure at the gastric cardia and its relationship to acid refluxed into the esophagus. In this study, pH patterns of the gastric cardia at baseline and during esophageal reflux were determined using ambulatory pH monitoring in normal volunteers. Methods: Ten volunteers with normal distal esophageal acid exposure underwent 18-h ambulatory pH monitoring studies with pH leads placed 5 cm proximal, 5 cm distal, and 10 cm distal to the proximal border of the LES. Results: Median LES length and pressure were 3.5 cm (range 2.5-4.5) and 28 mm Hg (18-48), respectively. Total cardia acid exposure was 45.2% with a wide range (1.076.1%) and was significantly different from esophagus (1.6; 0.2-5.9%) and stomach (87.5; 76.0-95.4%) (p < 0.001). Upright (49.8; 1.5- 77.0%) and recumbent (31.4; 0-75.1%) cardia acid exposure were not different. Patterns of baseline cardia acid exposure were characterized by: 1) prolonged periods of no acid exposure; 2) isolated brief episodes of acid exposure with stepwise clearances similar to the esophagus; 3) sustained repetitive vascillations between low and neutral pH; or 4) prolonged periods with pH <4 in the cardia. The majority (86.4%) of cardia acid exposures were < 1 min. in duration most consistent with patterns B and C. Esophageal reflux occurred during sustained repetitive vascillations in cardia pH (48%), prolonged periods of cardia acid exposure (33%), or with single transient exposures of acid reflux into the cardia then the esophagus (19%) with stepwise clearance in both. Conclusion: 1) Cardia acid exposure is present at a level intermediate between that of the esophagus and stomach; it is most commonly transient but may be continous, similar to the stomach. 2) Refluxed esophageal acid originates from a pool of acid distal to the cardia that then bathes the cardia in sustained, repetitive, or single acid exposures and occasionally travels into the esophagus.