In 1987, Richter and colleagues published the results of an esophageal motility study conducted on 95 normal healthy volunteers between the ages of 22 and 79. In accordance with these results, abnormal esophageal motility was defined on the basis of the percentage of manometric normal, ineffective, and simultaneous swallows and on lower esophageal sphincter dynamics during liquid swallows. For example, Richter and colleagues found that the mean amplitude of contraction in the distal body of the esophagus >180 mm Hg in association with wet swallows was above the 95% confidence interval of normal. Richter's study also showed a wide variation among individuals and that the mean distal esophageal contractile amplitude increased with age without sex predominance. Likewise, as no subjects had >20% simultaneous contractions (though a considerable number, 4%, had 10% simultaneous contractions), esophageal spasm was defined at the >20% mark.