Ambulatory 24-h esophageal pH monitoring: normal values, optimal thresholds, specificity, sensitivity, and reproducibility. - Jamieson,J.R.; Stein,H.J.; DeMeester,T.R.; Bonavina,L.; Schwizer,W.; Hinder,R.A.; Albertucci,M. (Am J Gastroenterol, 1992)