Esophageal motility disorders may be an explanation of dysphagia in patients after exclusion of esophageal structural lesions by endoscopy and radiography and eosinophilic esophagitis by histology. The best defined motility disorder is achalasia; however, other motility disorders such as diffuse esophageal spasm (DES), hypercontractile esophagus, and absent or weak peristalsis have also been reported with dysphagia.
Esophageal manometry characterizes the contractility of the esophagus to identify and classify motility disorders. High-resolution manometry (HRM) with esophageal pressure topography (EPT) analysis is now the method of choice to assess esophageal contractile function. These techniques were initially described by Clouse in the 1990s. The concept of HRM is to overcome the limitations of conventional manometric systems by using advanced electronic technologies. The key to this development involved vastly increasing the number of pressure sensors on the manometric assembly. Pressure sensors are placed with sufficient proximity to each other so that, by interpolating between adjacent sensors, intraluminal pressure can be viewed as a continuum along the length of the entire esophagus and adjacent sphincters. When HRM is coupled with improved sensor design, such that each sensor is circumferentially sensitive and capable of high-fidelity recordings, it also overcomes the fidelity and directionality limitations inherent in conventional water-perfused systems. The final technological advance that facilitated the widespread application of HRM to clinical manometry was the development of sophisticated plotting algorithms to display the hugely expanded manometric data set as colored EPT plots rather than as a multitude of overlapping line tracings. Together, these developments facilitate dynamic imaging of intraesophageal pressure as a continuum along the length of the esophagus with pressure magnitude depicted by spectral color. Fig. 1 depicts the typical pressure topography of both sphincters and the entire length of intervening esophagus during a swallow. The relative timing of sphincter relaxation, segmental esophageal contraction, as well as the position and length of pressure troughs between segments, are all readily demonstrated.
The use of intraluminal impedance to monitor the bolus movement within the gastrointestinal (GI) tract was first described by Silny in 1991. The technique is based on measurement of electrical impedance between closely placed electrodes mounted on an intraluminal probe. Impedance between each electrode pair depends on the nature of the luminal contents surrounding the electrodes. When the esophagus is empty, the impedance reflects the conductivity of the esophageal mucosa. Otherwise, it is indicative of surrounding intraluminal air (high impedance) or liquid (low impedance). With multiple pairs of impedance rings along the lumen of the esophagus, the spatial distribution and movement of air or liquid within the esophagus can be detected. Validation studies have verified that intraluminal impedance measurement has a high sensitivity and accuracy for tracking intraesophageal bolus movement and monitoring reflux. However, it is important to note that the technique is not sensitive to the volume of the bolus or refluxate; 1.0 mL of residue potentially yields the same signal as 10 mL.
In conjunction with HRM, impedance monitoring allows tracking the swallowed bolus in relation to EPT. Although the impedance data are ideally also displayed in a topographic format, the validated criteria for bolus presence within a segment is of a 50% decrease in impedance while a 50% increase toward the baseline value correlates with bolus exit. Swallows can then be classified as having complete bolus transit if bolus entry is seen at the most proximal site and bolus exit is recorded in all distal impedance-measuring sites, or incomplete bolus transit, if bolus exit is not identified at one or more of the distal impedance-measuring sites.
Achalasia
Achalasia is both the best-defined esophageal motor disorder and the one with the most specific treatment, making its accurate identification a key objective of clinical manometry. The manometric criteria for diagnosing achalasia are incomplete lower esophageal sphincter (LES) relaxation and absent peristalsis. One of the greatest gains realized with HRM over conventional manometry has been in refining the definition of both of these criteria, with the net effect of greatly improved accuracy in the identification of the varied contractile patterns of achalasia.
It is a common misconception that the LES (esophagogastric junction [EGJ]) normally relaxes completely to intragastric pressure after swallowing. In fact, this is distinctly unusual and even abnormal. Rather, the EGJ relaxes to a value that is close to intragastric pressure for a certain amount of time during the post-deglutitive period. Considerable effort has been expended in using EPT to define more precisely these vague terms of “close to intragastric pressure” and “certain amount of time.” Deglutitive EGJ relaxation occurs at a fixed time and place on EPT plots. Fig. 2 illustrates the location and relaxation of the sphincter during bolus transit relative to the pharyngeal swallow. In most instances, EGJ relaxation is measured in the region spanning from 2 cm above the proximal aspect of the EGJ at rest to the proximal stomach for a 10-second period commencing with upper esophageal sphincter (UES) relaxation. In the setting of normal peristalsis, the window terminates with the arrival of the peristaltic contraction, but in the setting of failed peristalsis, an arbitrary 10-second cutoff is established, and in the setting of a premature distal esophageal contraction, a very brief window of opportunity exists. Note that if sphincter elevation exceeds 2 cm, as evident by the position of the LES during the post-deglutitive contraction, the spatial limits for the measurement need to be adjusted accordingly. Once the spatial limits of the EGJ relaxation window are established, maximal EGJ pressure is then ascertained for each instant within the window—in essence, an e-sleeve measurement. The resultant data set then amounts to a history of EGJ residual pressure commencing at the instant of UES relaxation and ending either with the arrival of the esophageal contraction or 10 seconds later. However, it is overly simplistic to think of EGJ relaxation pressure as solely indicative of LES relaxation. Actually, at any one instant the e-sleeve pressure is the greatest of three possible contributions: LES pressure, crural diaphragm contraction, or intrabolus pressure as the swallowed water traverses the EGJ. Hence, the development of the EPT relaxation metric of the integrated relaxation pressure (IRP). The IRP is measured within the deglutitive window, capturing the axial movement of the LES and spanning from the time of initiation of the swallow until the arrival of the peristaltic contraction with the added stipulation that the relaxation pressure being reported represents the 4-second period of lowest EGJ pressure after the swallow (see Fig. 2 ). Table 1 illustrates the added yield of the IRP compared to the nadir LES or EGJ pressure in the detection of impaired EGJ relaxation in a series of well defined achalasia patients. This is of great significance because failing to detect impaired EGJ relaxation has the result of giving these patients an alternative diagnosis, most commonly misclassifying as ineffective esophageal motility or DES.
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