High-Resolution Esophageal Manometry: Techniques and Use in the Diagnosis of Esophageal Motility Disorders and for Surgical Decision Making

Technical Aspects

Esophageal manometry is a test in which intraluminal pressure sensors, either water perfused or solid state, are positioned axially within the esophagus to quantify the contractile characteristics of the esophagus and segregate it into functional regions. The probe/catheter is inserted transnasally and connected to a recording unit (via a hydraulic pump in case of perfused pressure sensors). Whereas conventional technique used probes with 3 to 8 pressure sensors spaced 3 to 5 cm apart, HRM typically uses 36 solid-state pressure sensors spaced at 1-cm intervals. The concept of HRM is to use a sufficient number of pressure sensors within the esophagus such that intraluminal pressure can be monitored as a continuum along the entire length of the esophagus, much as time is viewed as a continuum in line tracings of conventional manometry. Fig. 8.1 superimposes representative conventional and HRM recordings with the HRM displayed in EPT format. The most common currently available HRM catheters consist of 36 pressure sensors spaced 1 cm apart. These devices provide sufficient recording length (35 cm) for the recording to span from the hypopharynx to the stomach (with several intragastric sensors) without need for probe repositioning during the course of a study. HRM offers several theoretical advantages over conventional manometry: (1) the technique lends itself to standardized objective metrics of interpretation, (2) it is easier to perform studies of uniform high quality, (3) movement artifact attributable to a relative change in the position of a sensor and contractile zone (especially sphincters) is minimized, and (4) the process of interpretation is more intuitive and more easily learned by trainees naïve to either conventional or high-resolution manometric formats.

Manometric Protocol

Esophageal manometry is usually performed in the supine position. This position allows the testing of peristaltic function without the effect of gravity on bolus transit and esophageal contractile pressures are augmented when supine. Historically, using perfused pressure sensors, the supine position was mandatory to have all the sensors at the same height as the external pressure transducers, thereby avoiding pressure offsets secondary to hydrostatic pressure. With solid-state transducers, this is no longer an issue and studies can be performed in the upright position, which some argue to be more physiologic. However, all currently available normative data have been established in the supine position.

A typical manometry protocol consists of a 30-second basal period without swallowing followed by 10 test 5-mL water swallows. Test swallows are separated by at least 20 seconds to reestablish basal activity and avoid having deglutitive inhibition from the prior swallow modulating the subsequent swallow. The manometric diagnosis is based on the analysis of the 10 5-mL test swallows. Increased water volume (10, 20 mL) can be given to stress peristalsis, and multiple rapid swallows may be used to assess deglutitive inhibition, but these challenges have not yet been sufficiently standardized to serve as diagnostic criteria. However, multiple rapid swallows are a simple method for assessing the integrity of deglutitive inhibition, defects of which are thought to be responsible for some motility disorders. Finally, the consistency of the bolus can be varied using viscous solutions or solids such as marshmallow or bread. However, again, these challenges have not yet been sufficiently standardized to serve as diagnostic criteria.

Esophageal Pressure Topography

When HRM is coupled with sophisticated algorithms to display the manometric data as pressure topography plots, esophageal contractility is visualized with isobaric conditions among sensors indicated by isocoloric regions on the pressure topography plots. In EPT plots (or Clouse plots) the y-axis represents the axial length of the esophageal body, with the pharynx and upper esophageal sphincter (UES) at the top of the graph and the esophagogastric junction (EGJ) and proximal stomach at the bottom. The x -axis represents time, so that peristaltic pressure waves can be seen propagating to the right during swallows. Pressure is represented as color, with “hot” colors (red, orange) representing higher pressures and “cool” colors (green, blue) depicting lower pressures.

Fig. 8.2 depicts a normal swallow in a high-resolution EPT plot encompassing both sphincters and the intervening esophagus; the relative timing of sphincter relaxation and segmental contraction as well as the position of the transition zone are all readily demonstrated. The swallowing sequence is described as follows. The UES relaxation induced by swallowing is followed by a peristaltic contraction in the esophageal body that is dependent on the regional gradient of inhibitory neurons within the myenteric plexus. The peristaltic esophageal contraction is preceded by a period of latency or quiescence in the esophageal body and contractile activity is not generated until the period of inhibition or latency is supplanted by excitatory activity at that particular location. Swallow-induced EGJ relaxation also begins just after UES relaxation and ends when the propagated esophageal contraction reaches the EGJ. The peristaltic contraction is characterized by two major pressure troughs, one proximal and one distal (see P and D in Fig. 8.2 ). A middle pressure trough is sometimes evident, but this is variable among individuals. Another notable feature of peristalsis is an inflexion point in propagation velocity as the contraction nears the EGJ. This inflexion point, termed the contractile deceleration point (CDP), demarcates the initial segment of the esophageal contraction dominated by esophageal peristalsis from the later portion of the contraction during which ampullary emptying transpires. The CDP can be localized objectively by fitting tangential lines to the initial and terminal portions of the 30-mm Hg isobaric contour and noting intersection of the lines as illustrated in Fig. 8.2 .

Algorithm of Analysis Using Pressure Topography Parameters

The algorithm for classifying esophageal motor disorders using EPT is based on a systematic analysis that begins by separating the plot into two functional domains: the EGJ and esophageal body. This system for analysis was developed after the advent of HRM and relies on the use of computer calculations to measuring metrics specific to EPT. The resulting algorithm for HRM measurement and subsequent classification and diagnosis of esophageal contractility disorders has been termed the Chicago Classification. Drawing on an initial experience using the system, the Chicago Classification has subsequently been updated by international working groups to the current version 3.0 (v3.0). The remainder of the chapter will be based on this current iteration.

Chicago Classification analysis begins with an assessment of EGJ function because abnormal EGJ pressure morphology or impaired deglutitive EGJ relaxation can profoundly affect peristalsis and pressure topography within the esophageal body. EGJ abnormalities are also of important clinical significance because bolus transport depends on the balance among resistance through the EGJ, intrabolus pressure (IBP), and esophageal closure pressure behind the bolus. Consequently, the first step in analyzing esophageal motility should focus on the EGJ. Consistent with this, a stepwise analysis algorithm first characterizes EGJ pressure morphology (presence of hiatus hernia) and the adequacy of deglutitive EGJ relaxation. The implications of abnormal EGJ pressure morphology on clinical classification have yet to be fully defined, but physiologic data support the concept that there is a strong interaction between EGJ structure and esophageal function, as well as competence of the EGJ valve mechanism in preventing gastroesophageal reflux (GER). The consequences of impaired deglutitive EGJ relaxation are more obvious, leading to increased distal esophageal (or panesophageal) IBP. Hence, although EGJ pressure morphology will likely be incorporated into future diagnostic categories, the first branch point in the current scheme is of normal or impaired EGJ relaxation because this consistently affects esophageal function.

After defining EGJ anatomy and deglutitive relaxation, the next step in analysis is focused on the esophageal peristalsis. The topography pattern of individual swallows are each classified according to the Chicago Classification parameters shown in Table 8.1 . Earlier versions of the Chicago Classification focused on the integrity of peristalsis (i.e., whether breaks in the peristaltic waves occurred). However, subsequent studies demonstrated that significant breaks in peristalsis frequently occur in healthy individuals, especially at the transition zone in the proximal esophagus between striated and smooth muscle, and that these breaks are not a reliable measure for defining clinically relevant diagnostic categories. As a result, the Chicago Classification v3.0 focuses on assessing the effectiveness of individual swallows based on contractile vigor, or the summed pressure front of the peristaltic wave of each swallow, irrespective of breaks in the wave pattern. This is done by measuring the distal contractile integral (DCI), which can be conceptualized as the volume of the pressure topography graph in the peristaltic wave distal to the transition zone. Swallows are classified as failed, weak, normal, or hypercontractile, based on DCI. This method of analysis both simplifies the classification of swallows and makes it a more clinically relevant assessment of bolus clearance. Swallows are then further characterized by distal latency (DL) and peristaltic breaks to identify instances of premature contraction (i.e., spasm) or fragmented peristalsis (currently defined as a minor disorder of esophageal motility of unclear clinical significance).

In addition to the contractile pattern, each swallow is examined for an abnormal esophageal pressurization with the contractile activity. This is a unique feature of EPT as these patterns are much more evident in pressure topography compared with the conventional line-tracing format. After all test swallows are characterized, the study results are summarized using the classification algorithm, as presented in Fig. 8.3 and Table 8.2 .

Esophagogastric Junction Morphology

Both the lower esophageal sphincter (LES) and the surrounding crural diaphragm (CD) contribute to measured intraluminal EGJ pressure. The CD component is most evident during inspiration but probably also contributes a minor component to EGJ pressure during expiration. Thus there are two major confounding variables in describing EGJ intraluminal pressure: phase of the respiratory cycle and the relative positions of the LES and the CD. No consensus was ever achieved with conventional manometry on how to deal with either of these variables. Indeed, there was generally little recognition of the EGJ as a complex sphincter, instead simply referring to it as the LES on manometry studies. With HRM, the sphincteric contributions of the CD and LES become somewhat obvious and the relative localization of the LES and CD elements defines EGJ morphologic subtypes ( Fig. 8.4 ). The magnitude of CD augmentation of EGJ pressure during normal respiration is readily quantified. A retrospective analysis of the relationship between these attributes of EGJ pressure topography and GERD found that GERD patients had significantly greater CD-LES separation (i.e., hiatal hernia) compared with either controls or non-GERD patients. GERD patients also had significantly less inspiratory CD augmentation compared with controls or non-GERD patients. Furthermore, in a logistic regression model, only inspiratory augmentation was found to have a significant independent association with GERD, suggesting that CD impairment was the mediator of both the hiatus hernia and LES hypotension effects.

Finally, dynamic HRM studies during reflux monitoring revealed that this is not a static situation. Rather, GERD patients oscillated between types I and II EGJ conformations. Reflux events preferentially occurred during the periods of type II conformation characterized by a small separation of the two high-pressure areas. Paradoxically, in contrast to the findings related to the CD and EGJ morphology, it is less clear that any measure of basal EGJ pressure has much significance.

Esophagogastric Junction Relaxation

Incomplete deglutitive EGJ relaxation is an essential feature in the diagnosis of achalasia, and achalasia is not only the best-defined esophageal motor disorder but also the one with the most specific treatments. These features impart important clinical relevance on the accurate detection of incomplete deglutitive EGJ relaxation. Despite this cardinal significance, there has never been a unified convention for defining incomplete deglutitive EGJ relaxation with conventional manometry. Furthermore, numerous potential confounding factors exist, including CD contraction during respiration, esophageal shortening, hiatal hernia, IBP through the EGJ, sphincter radial asymmetry, and movement of the recording sensor relative to the EGJ. With HRM, the ease and reliability of measurement of EGJ relaxation is greatly improved. Pressure topography plotting facilitates accurate localization of the EGJ and the deglutitive relaxation window, as illustrated in Fig. 8.2 . An exploratory study comparing criteria for detecting impaired deglutitive EGJ relaxation within that relaxation window in a large group of patients and control subjects concluded that the optimal measure for quantifying deglutitive relaxation was the integrated relaxation pressure (IRP), with normal being defined as less than 15 mm Hg. The IRP is amenable to automated calculation, and conceptually it is the lowest average pressure for 4 seconds (either contiguous or noncontiguous) within the 10-second relaxation window ( Fig. 8.5 ). This single measure of deglutitive EGJ relaxation exhibited 98% sensitivity and 96% specificity for distinguishing well-defined achalasia patients from control subjects and patients with other diagnoses. It should be noted that the measurement of IRP is variable depending on the manometry probe and analysis software that is being used. The Chicago Classification v3.0 set the cutoff for normal at less than 15 mm Hg for the Sierra design catheters and less than 28 mm Hg for the Unisensor design. A model-specific cutoff value should be used when categorizing EGJ relaxation.

Contraction Vigor

The vigor of the distal esophageal contraction between the major pressure nodes P and D is quantified using the DCI. Conceptually the DCI corresponds to the volume of the distal contraction in dimensions of time, length, and amplitude between the proximal and the distal troughs using the 20-mm Hg isobaric contour at the base and expressed as (mm Hg-s-cm) ( Fig. 8.6B ). It is calculated by multiplying the mean pressure of the contraction (less 20 mm Hg), duration of the contraction, and the length of the esophageal segment between the proximal and distal troughs. Based on this value, swallows are classified as failed (DCI < 100 mm Hg-s-cm), weak (DCI > 100, but < 450 mm Hg-s-cm), normal (DCI from 450 to 8000 mm Hg-s-cm) or hypercontractile (DCI > 8000 mm Hg-s-cm). Failed and weak swallows are together classified as “ineffective” swallows.