Gastric acid
The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
Esophageal pH monitoring
In assessment of distal esophageal pH, the sensor is placed 5 cm above upper border of the lower esophageal sphincter (LES) determined by esophageal manometry. To measure proximal esophageal acid exposure the second sensor is placed 1-5 below the lower border of the upper esophageal sphincter (UES). The Bravo pH capsule is placed either transnasally based on manometric measurements, or following endoscopy. In transnasal placement the capsule is placed 5 cm above upper border of the LES, and in endoscopic placement 6 cm above gastroesophageal junction. The same applies to OMOM pH monitoring capsule.