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Interpretation of HRM/EPT studies can be performed in a stepwise, hierarchical fashion as described by the Chicago Classification working group [3, 4]. Since its inception, the Chicago Classification of esophageal motility disorders has undergone periodic updates guided by an international consensus group [3, 4, 21]; the consensus process to develop Chicago Classification version 4.0 is underway at the writing of this chapter. There are several caveats to consider when applying the Chicago Classification to EPT analysis. As previously mentioned, absolute values of EPT parameters are intended to reflect thresholds of normative values generated via a similar manometric test protocol and HRM‐assembly device (Table 8.1). Consequently, clinical interpretation of HRM should be based upon normative values generated with a similar catheter assembly and test protocol [8]. The difference between catheter assemblies most notably applies to the IRP. For the catheter designed by Sierra Scientific and subsequently marketed by Given Imaging, then Covidien, and most recently Medtronic, the upper limit of normal for the IRP is 15 mmHg, while for catheter assemblies that employ Unisensor technology, an IRP threshold of approximately 20 mmHg is more appropriate. Similarly, interpretation of manometry studies performed using bolus types or patient positions other than the standard 5 ml liquid supine test swallows described in the Chicago Classification should reflect normative values obtained in those conditions [8]. Furthermore, the Chicago Classification was devised to detect primary motor disorders in patients without previous foregut surgery or mechanical esophageal obstruction (e.g. esophageal stricture or large hiatal hernia) and should not be applied in patients with these conditions. However, acknowledging these factors, the concepts and patterns of EPT interpretation based on the Chicago Classification can be broadly applied to describe HRM findings with standardized and consistent terminology.

Figure 8.1 Esophagogastric junction (EGJ) morphology. Morphology of the EGJ is typically evaluated during the resting baseline period. With type I EGJ morphology (A), the high‐pressure zones associated with the lower esophageal sphincter (LES) and crural diaphragm (CD) are superimposed. With type II EGJ morphology (B), a small degree (< 3 cm) of separation is observed between the LES and CD, typically representing a small, often reducible hiatal hernia; the pressure inversion point occurs at the CD. With type III EGJ morphology (C), the separation between the LES and CD is > 3 cm and represents a hiatal hernia. Deep breaths aid in identification of the pressures inversion point (which occurs at the level of the CD in A, B, and C) and clarifying EGJ morphology by augmenting the inspiratory CD contraction.

Source: Used with permission from the Esophageal Center at Northwestern University.