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An initial step in interpreting an HRM study involves assessing the technical adequacy of the study, which includes confirming intragastric catheter placement by identification of the pressure inversion point. The EGJ morphology should be described, which simply refers to a description of whether or not a hiatal hernia is present (Figure 8.1). A hiatal hernia can be detected as a dual high‐pressure zone at the EGJ (Figure 8.1C). The distance in axial separation between the center of the LES (the more proximal of the two high‐pressure zones) and the crural diaphragm (CD, the more distal high‐pressure zone) should be noted, with values >1 cm indicative of hiatus hernia [24]. Finally, basal EGJ pressure should be assessed. The CD contributes substantially to basal EGJ pressure; thus the respiratory cycle needs to be accounted for in a measure of basal EGJ pressure. While this can be as simple as measuring an expiratory and/or inspiratory EGJ pressure, more comprehensive measures of basal EGJ pressure have been reported, such as the EGJ‐contractile integral (EGJ‐CI) [25, 26]. The EGJ‐CI uses a similar methodology to the distal contractile integral (DCI) with the measurement region of interest encompassing the LES and CD over the duration of three respirations, while the isobaric contour is set at gastric pressure. The measure is divided by the duration of the three respiratory cycles measured for standardization, making mmHg•cm the units of EGJ‐CI.

Figure 8.2 Esophageal pressure topography metrics. (A) An example of a normal swallow with intact peristalsis; (B) a swallow associated with esophagogastric junction (EGJ) outflow obstruction. Deglutitive lower esophageal sphincter relaxation is measured by the integrated relaxation pressure (IRP); the borders of the EGJ incorporated into the IRP measures are signified by the dashed orange lines. The contractile deceleration point (CDP; red star) is located by identifying the inflection point in propagation velocity along the 30 mmHg isobaric contour; in the setting of compartmentalized pressurization (B; identified by white *), the CDP is identified along an isobaric contour of greater pressure than the intrabolus pressurization. The distal latency is measured as the time from the onset of swallow to the CDP. Peristaltic vigor is measured by the distal contractile integral (DCI).

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

The assessment of basal EGJ characteristics and function carries clinical significance with regard to gastroesophageal reflux susceptibility; greater LES‐CD separation (type III morphology), reduced CD augmentation pressures, and low EGJ‐CI (generally <30 mmHg•cm) are associated with increased reflux as measured by pH‐metry or pH/impedance‐metry [25, 27–31]. Elevated basal EGJ pressures are also observed (a hypertensive LES), but the clinical relevance of this finding remains unclear [32].