Decreased Variation In Esophageal Acid Concentration In Different Phenotypes Of Symptomatic Gastroesophageal Reflux Disease

BackgroundHomeostatic physiologic systems are regulated to maintain a particular variable such as blood pressure within a restricted range with relatively low variation, and this variation is increased with disease. Fractal physiologic systems, on the other hand, are characterized by wide, complex variation of variables such as heart rate or the walking stride interval, and this variation is decreased with disease. The present report examines time-series recordings of esophageal pH from normal subjects and different GERD phenotypes to measure the distributions of esophageal pH values and the distributions of changes in esophageal acid concentrations. MethodsUsing Lyon consensus definitions of symptomatic GERD phenotypes, I analyzed 24-hour esophageal pH recordings from normal subjects (n=20), Functional Heartburn subjects (n=20), Reflux Hypersensitivity subjects (n=20), and nonerosive esophageal reflux disease (NERD) subjects (n=20). For each subject I calculated the distribution of pH values as well as the distribution of changes in esophageal acid concentrations. ResultsEsophageal pH values have a power law distribution in both normal and symptomatic GERD phenotypes, and esophageal acid concentrations vary over four orders of magnitude in each group. The variation in esophageal acid concentrations decreased progressively from normal subjects to Functional Heartburn subjects to Reflux Hypersensitivity subjects to NERD subjects. ConclusionsThe decreased variation in esophageal acid concentration in symptomatic GERD phenotypes represents changes associated with disease in a fractal physiologic system that shares characteristic features with other fractal systems where disease states have been associated with decreased variation of heart rate or walking stride interval.