A Short History of High-Resolution Esophageal Manometry

Abstract

High-resolution esophageal manometry (HRM) utilizes sufficient pressure sensors such that intraluminal pressure is monitored as a continuum along luminal length, similar to time viewed as a continuum on polygraph tracings in ‘conventional’ manometry. When HRM is coupled with pressure topography plotting, and pressure amplitude is transformed into spectral colors with isobaric areas indicated by same-colored regions, “Clouse plots” are generated. HRM has several advantages compared to the technology that it replaced: (1) the contractility of the entire esophagus can be viewed simultaneously in a uniform standardized format, (2) standardized objective metrics of peristaltic and sphincter function can be systematically applied for interpretation, and (3) topographic patterns of contractility are more easily recognized with greater reproducibility. Leveraging these advantages led to the current standard for the interpretation of clinical esophageal HRM studies, the Chicago Classification (CC), now in its fourth iteration. Compared to conventional manometry, HRM has vastly improved the sensitivity for detecting achalasia, largely due to the objectivity and accuracy of identfication of impaired esophagogastric junction (EGJ) relaxation. Additionally, it has led to the subcategorization of achalasia into three clinically relevant subtypes, differentiated by the contractile function of the esophageal body, and identified an additional disorder of EGJ outflow obstruction wherein esophageal peristalsis is preserved. Headway has also been made in understanding hypocontractile and hypercontractile conditions. In summary, HRM and the CC process have revolutionized our understanding of esophageal motility and motility disorders. Moving forward, there will always be remaining challenges, but we now have the tools to meet them.

Introduction

Prior to the introduction of high-resolution manometry (HRM) into clinical esophagology in the early 2000s, conventional line-tracing manometry was the standard for esophageal motility testing. Conventional perfused manometry, a major development in the 1970s, utilized external volume-displacement pressure transducers and a pneumo-hydraulic pump to push degassed water through a multilumen manometry catheter with each lumen ending in a side-hole recording site spaced 3–5 cm apart along the manometric catheter [1, 2]. Manometry catheters were made by hand from silicone or polyvinyl chloride extrusions and typically incorporate 3–8 lumens terminating in pressure recording sites. Of note, there was no agreed upon convention regarding an optimal array of pressure sensors and a wide variety of designs existed. Esophageal pressure changes were transmitted along the water column within the multilumen extrusion to the external volume-displacement transducers that generated line graph representations of esophageal pressure changes with test swallows [2, 3]. These were displayed on a polygraph as a series of pressure graphs in a stacked line-tracing format, initially printed on sheets of recording paper with written notations of catheter position to facilitate later analysis by hand. With the dawn of the personal computer age in the 1980s, this was subsequently converted to an electronic signal viewed on computer screens with electronic analysis software.

Measurement of the lower esophageal sphincter (LES) pressure was always a fundamental objective of a manometry study. However, making an accurate assessment of LES pressure with widely spaced side-hole pressure recording sites presented unique challenges on account of axial sphincter movement with respiration and swallowing. Hence, LES pressure was measured by pulling the recording sites across the LES either at 1 cm increments (station pull through) or at a controlled rate during suspended respiration (rapid pull though). Some centers went so far as to use a motorized device to pull the catheter across the LES at a defined rate allowing for estimates of LES length as well as pressure. These limitations prompted the development of a perfused sleeve positioned across the esophagogastric junction (EGJ), termed Dentsleeve after the innovator of that technology, John Dent [4]. The Dentsleeve was typically 6 cm in length and detected the greatest pressure existing anywhere along that length. Placement of the manometric assembly still required a stationary pull-through to identify characteristic respiratory pressure changes between the abdominal and thoracic cavities in order to localize the EGJ. The catheter was then repositioned with the sleeve sensor across the EGJ [1].

In summary, there were a variety of sensor technologies including solid-state transducers, circumferentially sensitive transducers, perfused ports, and the Dentsleeve device, each optimized to study the contractile activity of a particular area of interest, be that the upper esophageal sphincter (UES), esophageal body, or EGJ. However, somewhat inevitably, what is optimized to study one area of interest leads to compromise in the assessment of another. Hence, there were a staggering number of variables in the technique of esophageal manometry rendering the performance and interpretation of recordings more an art than science. Herein lies the key to understanding the advantages of high-resolution manometry. Thanks to advances in transducer technology, computerization, and graphic data presentation, esophageal contractile activity following a swallow can be portrayed in a complete and accurate manner with the potential to greatly simplify and standardize the clinical manometric study.

High-Resolution Manometry: A Space Time Continuum of Intraluminal Pressure

Esophageal HRM, conceived in the early 1990s by the late Ray Clouse, is radically different from conventional manometry in both data acquisition and in the display of pressure data [5]. Historically, recording fidelity for manometric systems focused mainly on the frequency content of esophageal contractile waves at a given locus within the esophagus or pharynx. Spoken another way, the focus was on the time resolution of the recording. The frequency response required to reproduce esophageal pressure waves with 98% accuracy is 0–4 Hz, while that required for reproducing pharyngeal pressure waves is 0–56 Hz [6]. Hence, a transducer of fairly limited frequency response such as a small water perfused lumen with a side-hole sensing site and an external pressure transducer will suffice for recording distal esophageal pressures, whereas a solid-state transducer of extended frequency response will accurately record both proximal and distal esophageal pressures. However, simply focusing on the time resolution of the recording at a given intraluminal site begs the question of spatial resolution of the recording between manometric sites. Remember, conventional manometric systems utilize 3–8 pressure sensors generally spaced 3–5 cm apart. Ray Clouse explored the impact of data acquired from closely spaced recording sites by continuously repositioning a conventional catheter, 1 cm at a time, and obtaining additional water swallows at each position until the entire length of the esophagus was traversed. When the pressure graphs from these swallows were aligned and superimposed, the scaffolding for the modern day HRM started coming into shape, albeit the composite pressure data were from the separate swallows. Using this methodology, Ray concluded that with 1 cm sensor spacing there was essentially no data loss between sensors. Hence, pressure data could then be digitized and the gaps between sensors filled in by interpolation yielding a spatial continuum of pressure values along the entire length of the esophagus [7, 8]. Finally, isobaric contours were drawn at designated pressure increments, such that the pressure profile of a swallow could be visualized from above similar to a weather map of barometric pressure [8, 9] (Fig. 1).

Fig. 1.

Early schematic of the derivation of a Clouse plot. A 21-channel perfused manometry catheter with recording sites spaced at 1 cm intervals. B Twenty-one pressure tracings obtained from the distal esophagus with multiple interpolated pressure tracings between each of the 21 recording sites. C Colored isobaric contour lines are drawn across all of the line tracings completing the process of interpolation. D High-resolution manometry image (Clouse Plot) is viewed as if flying over the pressure topograph

To further visualize the process of converting conventional manometry into HRM as we know it today, consider Fig. 2 depicting how HRM enhances the visualization of sphincter relaxation. Figure 2 shows a recording from 10 manometric sensors spanning a 9 cm length of lumen from the pharynx to proximal esophagus [10]. Note that the individual line tracings are quite distinct and any manometric measurement made, be it maximal pressure, relaxation interval, or minimal relaxation pressure varies depending on which line you make that measurement from. With HRM, you use data from all of the sensors and interpolate between adjacent sensors as well [7–9, 11]. Illustrating this conversion, in Panel B of Fig. 2, the individual data points corresponding to the 10 pressure values at time t₁ are extracted from Panel A and a curvilinear interpolation is applied between adjacent recording sites representing a spatial continuum of proximal esophageal pressure at the time instant t₁. In order to now portray both time and space as a continuum, the magnitude of pressure at each x,t coordinate is encoded as a spectral color on an isobaric contour plot. This transformation is illustrated in Panels C and D in which the scale for translation of horizontal deflection into color is illustrated for t₁ in panel C and then applied to the entire 4 s recording in panel D. Now, examining the isobaric contour plot in Fig. 2D, not only can one make a reproducible measurement of the UES relaxation interval, no longer confounded by movement of the sensor or sphincter, but one can also make a quantitative measurement of intrabolus pressure within the sphincter during relaxation [12].

Fig. 2.

High-resolution manometry recording spanning from the hypopharynx to the proximal esophagus with ten manometric sensors spaced at 1 cm intervals. Panel A illustrates the raw data from the individual pressure sensors while panels B–D illustrate the process of transforming this into a spectral isobaric contour (Clouse) plot. In Panel B, the individual pressure values for from each manometric sensor are extracted for a single instant in time (t₁). A computer algorithm is then used to interpolate between these data points to complete the spatial pressure variation plot for time t₁. In Panel C, spectral colors are introduced as a means of quantifying pressure so that the entire isobaric contour plot of the full range of sensors can be summarized in Panel D. Note that the data in Panel C correspond to the line t₁ in Panel D. Adapted from Pal et al. [10]

For a time, further evolution of HRM was constrained by the limitations of manometry technology. There was only so far one could go with multilumen water perfused manometric assemblies. Ray Clouse tested these limits using an extruded 21-lm silicon water perfused catheter prototype along with customized computer software facilitating the introduction of perfused HRM to clinical esophagology at Washington University in St. Louis in the mid-1990s [7, 8]. For the first time, esophageal peristalsis was recognized as a synchronized and coordinated chain of contracting muscle segments, anchored by a sphincter at either end [9]. However, since the catheter had only 21 pressure recording sites and the topographic images were not visible to the operator during data acquisition, HRM remained dependent on the conventional manometric technique of stationary pull-through to localize the LES and only two-thirds of the esophagus could be interrogated without repositioning the assembly. Furthermore, the cumbersome behind-the-scenes preparation work characteristic of conventional manometry persisted, now requiring calibration and purging of air bubbles in each of 21 pneumohydraulic channels prior to every HRM procedure.

The technology behind esophageal HRM enjoyed a quantum leap in the early 2000s through a collaborative effort between the Washington University investigators and Sierra Scientific Inc (subsequently acquired by Medtronic), founded by Thomas Parks, PhD. The key innovation was the application of a proprietary pressure transduction technology (TactArray^™) into manometric assemblies. Using that technology, Sierra designed a solid-state manometric assembly (O.D. 4.2 mm) with 36 circumferentially sensitive sensors spaced at 1 cm intervals sufficient length to span from the pharynx to the stomach encompassing the entire esophagus (Fig. 3). Each of the 36 pressure sensing elements detected pressure over a length of 2.5 mm in each of 12 radially dispersed sectors. The 12 sector pressures are then averaged, making each of the 36 sensors a circumferential pressure detector with the extended frequency response characteristic of solid-state manometric systems and free of the hydrostatic influences characteristic of water perfused systems. The response characteristics of each sensing element were such that they could record pressure transients in excess of 6000 mmHg/s and were accurate to within 1 mmHg of atmospheric pressure for measurements obtained during the final five minutes of the study, immediately prior to the time of thermal recalibration. Using the longer catheter and new software, color plots of HRM recordings could be viewed in real time. The manometry protocol finally broke free from the need for assembly repositioning and the supine-only position for data acquisition associated with the hydrostatic effects of the water perfused systems. With the resultant real-time recordings, the positions of the UES, LES, and crural diaphragm were instantly apparent and it was immediately evident that esophageal shortening during peristalsis or transient LES relaxation not only occurred, but occurred with sufficient magnitude to reposition the LES beyond what would be tracked with conventional sleeve LES sensors [13]. Many motor disorders, especially achalasia, were associated with recognizable HRM patterns, often allowing diagnoses to be made with pattern recognition alone [14]. However, the motility audience was not immediately accepting of the new technology and universal acceptance of HRM took several years of additional research to demonstrate its clear benefits over conventional manometry [15].

Fig. 3.

Sierra solid-state manometric assembly with thirty-six sensors spaced at 1 cm intervals. Each pressure sensor consists of 12 radially dispersed sensing elements that are 2.5 mm in length. Sector pressures are averaged within each sensor making it circumferentially sensitive. Figure used with permission from the Esophageal Center at Northwestern

With the untimely passing of Ray Clouse, the next innovations in HRM technology emerged from Northwestern University in Chicago, where Peter Kahrilas, John Pandolfino, and Sudip Ghosh had been collaborating with Ray Clouse and Tom Parks to develop standardized analytic algorithms for the newly introduced technology. Their introduction of novel software-based tools to interrogate esophageal motor function went a long way in facilitating the assimilation of HRM to widespread clinical use. Since data were collected, processed, and displayed electronically, metrics based on software tools could be utilized to address key elements of HRM interpretation. The integrated relaxation pressure (IRP) was developed to standardize the assessment of swallow-induced EGJ relaxation, defining the median 4-s nadir of EGJ pressure in the 10-s post swallow period independent of pressure transients and crural diaphragm (CD) contractions [16]. The distal contractile integral (DCI) addressed vigor of esophageal smooth muscle contraction, taking length, amplitude, and duration of contraction into consideration. The distal latency (DL) measured the timing of peristalsis, from UES relaxation to arrival of the peristaltic wave at the contractile deceleration point in the distal esophagus. Normative values were developed from study of large numbers of healthy volunteers and applied to symptomatic patients to generate meaningful thresholds that defined abnormal motor function (Fig. 4). Finally, use of these software tools was demonstrated to predict clinical outcome in achalasia in a landmark study published in 2008 by the Chicago group [17]. This marked the turning point in the widespread acceptance of HRM as a clinical tool with clear advantages over conventional manometry. Over the past decade, further technological and procedural advances have solidified the role of HRM as the cornerstone of modern-day esophageal motor assessment.

Fig. 4.

Key Chicago Classification (CC) metrics used in the interpretation of clinical HRM studies. The timing of the swallow is delineated by the onset of upper esophageal sphincter (UES) relaxation. Swallow-induced EGJ relaxation is quantified by the integrated relaxation pressure (IRP), assessed in the 10-s post deglutitive box indicated by the dotted rectangle. Using e-sleeve methodology, the minimal pressure (from top to bottom, e.g., 25–31 cm recording sites in this illustration) at each instant within that rectangle is calculated and the IRP is the median of the 4 s with the lowest nadir pressures. The distal contractile index (DCI) is an expression of the vigor of the peristaltic contraction in the smooth muscle segment of the esophagus, spanning from the first major pressure node, P to the last major pressure node, D. The DCI is calculated as the product of pressure multiplied by time, multiplied by length of that contractile segment, expressed in units of mmHg s cm. The distal latency (DL) is a measure of the timing of the peristaltic contraction in the distal esophagus relative to the onset of the swallow and is used to identify premature contractions. Hence, the onset is UES relaxation and the offset is the contractile deceleration point (CDP), which physiologically represents the transition from peristaltic clearing to phrenic ampullary emptying (restitution of the LES). The CDP is identified as the inflection point of the 30-mmHg isobaric contour (sometimes termed the inflection of the hockey stick) in the 2 cm region proximal to the EGJ. Figure used with permission from the Esophageal Center at Northwestern.

The Chicago Classification of Motor Disorders

With the development of novel software tools to interrogate HRM Clouse plots, it became apparent that a standardized HRM classification scheme would be beneficial for the characterization of these newly characterized physiological parameters. The concept of the Chicago Classification stems from a 2007 meeting in Paris of the three founding members: John Pandolfino, Arjan Bredenoord, and Mark Fox. They envisioned an international collaboration of esophagologists, working together to push the field forward and resolve competitive factions that had been impeding progress in the field. Inspired by the seminal contributions of Ray E. Clouse (1951–2007) [5], the group decided to cooperatively build the International High-Resolution Manometry (HRM) Working Group. In fact, the first description of the “Chicago Classification” (CC) was in a publication authored by Mark Fox and Arjan Bredenoord in 2008 (CCv0.5) setting the stage for the inaugural meeting of the International HRM Working Group in San Diego later in 2008 [18]. The CC was conceptualized as a standardized approach to the interpretation of clinical HRM studies enabling clinicians worldwide to ‘speak the same language’, ending the Tower of Babel situation in which investigators from around the world applied differing names and definitions to the same conditions. This initiative resulted in the publication of CCv1.0 in 2009, although no version number was applied at the time [19]. Key to the implementation of the CC was the application of metrics (e.g., IRP, DCI, DL) that had been validated against independent measurements of esophageal function (e.g., radiology) and a hierarchical diagnostic system in which disorders of EGJ function (e.g., achalasia) were prioritized over major and minor disorders of peristalsis. A major advancement attributable to adoption of the CC was the recognition of achalasia subtypes [17] along with another puzzling disorder of EGJ outflow, termed EGJ outflow obstruction [20] (Fig. 5). As a tribute to its success, the publication of the CC spurred a tremendous amount of research and collaboration from centers around the world resulting in numerous proposals for refinement and revision. The first major CC update (CCv2.0, although still not branded with a version number), was endorsed by several international motility societies, and formally presented at the first meeting of the International HRM Working Group in Ascona in 2011 [21]. Subsequently, an expanded International HRM Working Group met in Chicago in conjunction with DDW 2014 to formulate the CCv3.0 that was formally presented at Ascona II in 2015 [22]. As a testimonial to its impact that publication (CC v3.0) had more citations than any other 2015 paper in Neurogastroenterology and Motility. The CC had achieved its goal and become the universal classification scheme of esophageal motor disorders in HRM worldwide.

Fig. 5.

Achalasia subtypes and bona fide EGJ outflow obstruction. Type I Achalasia: integrated relaxation pressure (IRP) is elevated with failed peristalsis (distal contractile index (DCI) < 100 mmHg s cm), and without panesophageal pressurization. Type II Achalasia: IRP is elevated with failed peristalsis and panesophageal pressurization to > 30 mmHg is observed in ≥ 20% of test swallows. Note that this recording was obtained with a HR impedance manometry catheter with the impedance signal (evident by the purple) showing retained fluid in the distal half of the esophagus. Type III Achalasia: IRP is elevated with a normal DCI, and a reduced distal latency. EGJ outflow obstruction: IRP is elevated with preserved peristalsis and compartmentalized pressurization between the peristaltic contraction and the EGJ. Note the differences between the spatial pressure variation (SPV) plots to the right of the type III achalasia and EGJ outflow obstruction panels. The SPV plots illustrate the top-to-bottom pressure profile within the Clouse plot at the time indicated by the black dashed line. In type III achalasia this has multiple peaks indicating multiple points of luminal closure, presumably a “corkscrew” on an esophagram, while with compartmentalized pressurization, the zone of pressurization is a flat plateau, indicating pressurization within a chamber sealed at both ends. Figure used with permission from the Esophageal Center at Northwestern

Apart from updating the CC to keep pace with interval developments, CC v3.0 also formalized the concept of the CC as a living document, meritorious of a version number. Inevitably, this led to a formalized process of further refinement and CC v4.0. Hence, the International HRM Working Group, now expanded to 52 members, worked for two years to develop the CCv4.0 [23, 24]. In addition to providing an updated classification scheme, priorities of CCv4.0 were to involve a diverse group of international experts, to apply more rigorous methodology in literature review and consensus development, to standardize the clinical HRM protocol, and to provide guidance on therapeutic considerations. Although much changed with CCv4.0, the essence remained. Compared to CCv3.0, there are four key modifications to the schema (Fig. 6). First, further manometric and non-manometric evaluation is required to arrive at a conclusive, actionable diagnosis of EGJOO. This addressed the Achilles heel of CCv3.0, namely identifying the subset of clinically relevant cases of EGJOO. Second, EGJOO, DES, and hypercontractile esophagus were recognized as three manometric patterns that required outside validation, e.g., associated obstructive esophageal symptoms, to be considered clinically relevant. Third, the standardized manometric protocol should ideally include supine and upright positions as well as the additional manometric maneuvers such as the multiple rapid swallows (MRS) and rapid drink challenge (RDC). Solid test swallows, post-prandial testing, and pharmacologic provocation can also be considered in particularly challenging circumstances. Finally, the definition of ineffective esophageal motility (IEM) became more stringent, but also less complex, now encompasses frag-mented peristalsis which had been a separate entity in CC v3.0. As such, CCv4.0 no longer distinguishes between major versus minor motility disorders but, rather, separates disorders of EGJ outflow from disorders of peristalsis and highlights the need for ancillary testing with a timed barium esophagram (TBE) and or functional luminal imaging probe (FLIP) to resolve borderline cases.

Fig. 6.

Scheme of the Chicago Classification (CC) v4.0. In a major departure from CC v3.0, disorders of EGJ outflow and disorders of peristalsis are segregated rather than viewed in a hierarchical scheme. The HRM protocol has also been standardized and often necessitates the interpretation of upright swallows, multiple rapid swallows (MRC), and a rapid drink challenge (RDC) in addition to 10 supine swallows. The biggest change of all comes in the characterization of EGJ outflow obstruction (EGJOO) which now requires secondary verification of outflow abnormality with either a timed barium esophagram (TBE) or a functional luminal imaging probe (FLIP) study. Ineffective esophageal motility (IEM) has also been redefined and now grouped with disorders of peristalsis rather than being relegated to a “minor’ disorder of peristalsis. Figure used with permission from the Esophageal Center at Northwestern

Advantages of High-Resolution Manometry Over Conventional Manometry

Compared to conventional line-tracing based esophageal manometry, HRM has several advantages. Simplification of the procedure for both the operator and the patient, shorter time required for data acquisition, use of standardized metrics for interpretation, and intuitive display facilitating learning by trainees and naïve clinicians stand out as clear advantages [18, 25].

Anatomic and Technical Gains

With the modern solid-state catheters that span the entire esophagus, both sphincters and the EGJ can be visualized during data acquisition, which shortens procedure time and reduces patient discomfort [26]. Real time Clouse plots allow the operator to manipulate the catheter or adjust the study protocol to obtain high-quality data, reducing the likelihood of imperfect studies [27]. Placement of pH and pH-impedance catheters can be facilitated by convenient identification of the proximal margin of the LES. The morphology of the EGJ can be determined by evaluating the relationship between the LES and CD, now characterized into three morphologic HRM subtypes with implications on reflux exposure and GERD pathophysiology [28, 29].

Accuracy of Diagnosis

When compared to conventional line-tracing format, advanced motility experts demonstrated better accuracy while interpreting HRM Clouse plots, with higher inter-rater agreement [30]. A clinical trial where 247 patients with dysphagia were randomized to either HRM or conventional manometry demonstrated a higher diagnostic yield for achalasia with HRM, and a higher likelihood of earlier diagnosis with HRM over conventional manometry [31]. In an international prospective blinded study involving 40 diagnostic HRM studies and 36 practitioners, inter-reviewer agreement was substantial for achalasia subtypes 1 and 2 (κ > 0.7), and modest for other motor diagnoses (κ > 0.34), demonstrating acceptable agreement for important motor diagnoses among motility providers in a wide range of clinical settings [32].

Upright Swallows

The supine position for motility testing was initially adopted partly to circumvent the role of gravity in bolus transit, but also because perfused conventional manometry required calibration to the supine position. The adoption of electronic pressure sensors set the manometric procedure free from testing exclusively in the supine position, and providing the option of additional swallows in the upright seated position [33]. Since bolus transit is assisted by gravity while upright, obstructive motor findings on HRM and bolus retention on HR impedance manometry that persists in the upright position has particular significance. An abnormal supine IRP that remains elevated > 12 mmHg while upright associates with radiographic evidence of impaired barium transit [34]. In contrast, if abnormal supine IRP corrects to < 12 mmHg during upright swallows, especially in the context of intact esophageal peristalsis and no obstructive symptoms, observation or non-permanent therapies directed at the EGJ may be more prudent. Addition of upright swallows to a standard HRM or HR impedance manometry (HRIM) protocol can therefore augment interpretation of abnormal IRP, and refine diagnosis of EGJ outflow obstruction.

Provocative Maneuvers

Provocative measures have been extensively studied in the past decade to stress the esophagus or the EGJ, using repetitive swallowing [35, 36], increased bolus volume [37], solid swallows and meals [38], particularly when motor abnormalities detected during the standard HRM protocol does not adequately provide context to the patient’s presentation.

Multiple rapid swallows, the most commonly used provocative measure [39], is performed by administering five 2 mL swallows in rapid succession while supine [40]. This maneuver assesses deglutitive inhibition, where both the esophageal smooth muscle and LES completely relax during repetitive swallowing when inhibitory pathways are intact. More importantly, the period of relaxation is followed by an augmented esophageal peristaltic contraction after the final swallow of the sequence when esophageal excitation and smooth muscle function are both intact [35, 40]. This augmentation is quantified using the MRS DCI to mean single swallow DCI ratio, and contraction reserve is present when the ratio is > 1 [40]. Since there can be variability between MRS attempts, a minimum of three MRS maneuvers may be needed for demonstration of a consistent pattern [41]. In patients with IEM, the presence of contraction reserve is associated with a lower likelihood of post fundoplication dysphagia, and lower acid exposure times (AET) [42, 43].

The rapid drink challenge consists of 100–200 mL of fluid administered through a straw while upright in the seated position. In healthy volunteers, the esophagus is converted into a passive conduit during RDC, with profound LES relaxation, inhibition of esophageal body peristalsis, and lack of pressurization or impedance bolus presence in the esophagus [44]. In the presence of latent or overt EGJ obstruction, the increased trans-EGJ pressure gradient manifests as esophageal pressurization, shortening or contraction, with an elevated IRP that correlates with severity of dysphagia on validated questionnaires [45–48]. The RDC is particularly useful when standard supine HRM is inconclusive in patients with esophageal-type dysphagia symptoms, where a positive RDC may prompt alternate testing for obstructive processes using barium radiography (especially solid bolus barium swallow or timed upright barium esopha-gram) or FLIP [49].

Some patients with persistent dysphagia and inconclusive test results may benefit from administration of solid boluses or a standardized test meal (STM) during HRM or HRIM [38, 50]. Similar to RDC, obstructive features may be identified during STM, thereby increasing the diagnostic yield of major motor disorders, and of contraction reserve. However, the test is cumbersome, not widely adopted by motility laboratories, and is likely to remain a niche procedure used under special circumstances to evaluate refractory symptoms [39].

Summary

Substantial gains have been made in our understanding of esophageal motor processes with HRM, with significant ease of acquisition and interpretation of HRM studies. Paradigms and parameters from conventional manometry have been largely replaced HRM-specific parameters, which are more intuitive and easier to understand. The process of acquisition, analysis, and reporting has become standardized around the world with the Chicago Classification, now in version 4.0.