catheter under sedation with endoscopic guidance may be necessary. However, performance of the manometry test requires an alert and awake patient, so it cannot be done until after the sedative effects have cleared. This practice may alter the results of the manometry, as both benzodiazepines and opioids used for conscious sedation can cause modest changes in esophageal motor findings, most notably causing increased LES relaxation pressures with opioids [16–19]. Additionally, the added time that the HRM catheter resides in the esophagus can exaggerate the thermal drift associated with solid‐state pressure sensors, potentially making the measurements less accurate [20].
In the setting of abnormal esophageal anatomy requiring an endoscopic assist in placing the manometry catheter, it is important to note that solid‐state HRM assemblies are very easily damaged and should not be grasped with any endoscopy accessories: foreign‐body retrieval devices, forceps, or snares. Instead, the tip of the endoscope should be maneuvered to nudge the tip of the HRM catheter as the catheter is advanced until appropriate positioning is obtained. This can be tedious, but the alternative of a damaged catheter is followed by an expensive repair or replacement.
Baseline evaluation
After allowing a brief period for patient acclimation to the catheter, a baseline of resting pressures is obtained during at least 30 s of restful breathing devoid of swallows. This allows for evaluation of the resting EGJ pressure and EGJ morphology. At the conclusion of the baseline testing period, we have the patient take three deep breaths to aid in the evaluation of the EGJ morphology (Figure 8.1).
Test swallows
The standard manometric protocol involves ten 5 ml liquid swallows performed in the supine (or semi‐supine, e.g. head raised 30 degrees) position [3, 4, 21]. While acknowledging that this position does not mirror ingestion in real life, it is a form of stress test for the esophagus to uncover motor abnormalities, analogous to running on a treadmill during a cardiac stress test. Further, standardization and consistency in the manometric test protocol are important as differences in bolus size, consistency, and patient position can all affect the pressure output [8]. Using the IRP as an example, when compared with a 5 ml liquid, supine swallow, the IRP would increase with larger bolus volume or thicker bolus consistency (e.g. viscous or solid) and decrease in the upright posture [8, 22, 23].
While the supine liquid swallow protocol forms the standard assessment and the basis for classification of esophageal motor disorders, restricting the study to only these 10 swallows carries limitations of both potentially missing clinically significant abnormalities in symptomatic patients and potentially “over‐calling” some abnormalities – EGJ outflow obstruction in particular. Hence, various additional maneuvers to supplement the standard supine liquid swallows have been proposed and are gaining interest in recent years. While not an exhaustive list, these potentially include upright liquid swallows, viscous swallows, solid bolus swallows, multiple rapid swallows, a rapid drink challenge, a solid test meal, and post‐prandial monitoring. These are discussed in greater detail next.
Interpretation of high‐resolution manometry and esophageal pressure topography
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.
Step 1: Evaluate EGJ morphology and tone
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.