Although not part of the current classification of ineffective or weak esophageal motility, the distal contractile integral (DCI) provides further assessment of global distal esophageal circular muscle strength. The DCI is calculated as the product of mean amplitude of the contraction (excluding pressure below 20 mmHg) from the transition of the striated to smooth esophageal muscles (proximal pressure trough) to the proximal border of the LES by duration and by length and gives an overall value of the circular muscle strength of the distal esophagus. To date, the DCI has largely been used to define hypercontractility, focusing on the upper limits of normal, differentiating hypercontractility from normal contractions, rather than the lower limits of esophageal motility. Figure 20.3 shows a normal esophageal body contraction in esophageal pressure topography and its corresponding line tracing in a patient with distal contraction amplitude and DCI within normal limits. A limitation of the automated DCI calculation provided by the analysis software is that repetitive pressure signals separated from the esophageal contractile complex such as vascular artifacts are included in this calculation. This may lead to artifactual overestimation of the circular contraction strength in patients with a hypocontractile esophagus [10]. The lower limit of the DCI, expressed by the 5th percentile of asymptomatic controls is 500 mmHg • cm • s.