Esophageal pH monitoring developed a dependable external reference electrode. Using this technique to monitor esophageal acid exposure patients for periods up to 24 hours, DeMeester and Johnson were able to identify the most important parameters of esophageal acid exposure, and they developed a composite pH score to quantify gastroesophageal reflux. The initial 24-hour pH studies required hospitalization until the introduction of microcircuits in the 1980s that allowed portable esophageal pH monitoring in an outpatient setting. Gastroesophageal reflux disease (GERD) is a common disease in western countries. In the United States, 7% of the population experiences heartburn daily and 44% at least once a
Glutamic acid The radical corresponding to glutamate is called glutamyl. When glutamic acid is dissolved in water, the amino group (-) may gain a proton (), and/or the carboxyl groups may lose protons, depending on the acidity of the medium. In sufficiently acidic environments, the amino group gains a proton and the molecule becomes a cation with a single positive charge, HOOC-CH()-()-COOH. At pH values between about 2.5 and 4.1, the carboxylic acid closer to the amine generally loses a proton, and the acid becomes the neutral zwitterion OOC-CH()-()-COOH. This is also the form of the compound in the crystalline solid state.