The function of the esophagus is transporting nutrients from the oropharyngeal cavity to the stomach. This is achieved by coordinated contractions and relaxation of the tubular esophagus and the upper and lower esophageal sphincter. Multichannel intraluminal impedance monitoring offers quantification of esophageal bolus transit and/or retention without the use of ionizing radiation. Combined with conventional or high-resolution manometry, impedance measurements complement the quantification of esophageal body contraction and sphincter relaxation, offering a more comprehensive evaluation of esophageal function. Further studies evaluating the utility of quantifying bolus transit will help clarify the role and position of impedance measurements.
Key points
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Esophageal manometry (both conventional and high-resolution) assess primarily the contractility of the tubular esophagus and relaxation of sphincters.
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Intraluminal impedance measures bolus presence and transit in the esophagus without radiation, allowing for a virtually unlimited number of observations.
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Combined impedance manometry (MII-EM) and high-resolution impedance manometry (HRiM) offer a comprehensive evaluation of the esophageal function, including esophageal motility and bolus transit.
Introduction
The function of the esophagus is transporting liquids and solids from the oropharyngeal cavity into the stomach. This is achieved by the coordinated contraction of the pharyngeal musculature, timely relaxation of the upper esophageal sphincter (UES), and esophageal peristalsis and relaxation of the lower esophageal sphincter (LES). This carefully scripted interplay of striated and smooth muscles is triggered by the cranial nerves, coordinated by a vagal and intrinsic esophageal network of neurons. A disturbance of this system leads to esophageal symptoms such as dysphagia and/or chest pain.
Testing of the esophageal function includes evaluating pharyngeal and esophageal peristalsis and relaxation of the upper and lower esophageal sphincter, as well as assessing esophageal bolus transit. Esophageal motility is quantified using esophageal manometry and in recent years more often by high-resolution manometry (HRM) with esophageal pressure topography (EPT) representation. Esophageal bolus transit has traditionally been assessed by video fluoroscopy, a method that allows visualizing the shape and progression boluses through the esophagus. The gold standard video fluoroscopy is limited by the ionizing radiation used during testing. Thus, researchers and clinicians have been looking for alternative methods to quantify esophageal bolus transit.
One alternative to fluoroscopy in assessing esophageal bolus transit is multichannel intraluminal impedance (MII). Measuring resistance to alternating current (impedance) in the esophageal lumen MII overcomes the limitation of video fluoroscopy, allowing quantification of esophageal bolus transit for virtually an unlimited number of swallows. This article summarizes studies validating this method, establishing normal values and the application of this method in clinical research and daily practice as identified by searches in PubMed for “esophageal impedance,” “multichannel intraluminal impedance,” “impedance manometry,” and “high-resolution impedance manometry.”
Introduction
The function of the esophagus is transporting liquids and solids from the oropharyngeal cavity into the stomach. This is achieved by the coordinated contraction of the pharyngeal musculature, timely relaxation of the upper esophageal sphincter (UES), and esophageal peristalsis and relaxation of the lower esophageal sphincter (LES). This carefully scripted interplay of striated and smooth muscles is triggered by the cranial nerves, coordinated by a vagal and intrinsic esophageal network of neurons. A disturbance of this system leads to esophageal symptoms such as dysphagia and/or chest pain.
Testing of the esophageal function includes evaluating pharyngeal and esophageal peristalsis and relaxation of the upper and lower esophageal sphincter, as well as assessing esophageal bolus transit. Esophageal motility is quantified using esophageal manometry and in recent years more often by high-resolution manometry (HRM) with esophageal pressure topography (EPT) representation. Esophageal bolus transit has traditionally been assessed by video fluoroscopy, a method that allows visualizing the shape and progression boluses through the esophagus. The gold standard video fluoroscopy is limited by the ionizing radiation used during testing. Thus, researchers and clinicians have been looking for alternative methods to quantify esophageal bolus transit.
One alternative to fluoroscopy in assessing esophageal bolus transit is multichannel intraluminal impedance (MII). Measuring resistance to alternating current (impedance) in the esophageal lumen MII overcomes the limitation of video fluoroscopy, allowing quantification of esophageal bolus transit for virtually an unlimited number of swallows. This article summarizes studies validating this method, establishing normal values and the application of this method in clinical research and daily practice as identified by searches in PubMed for “esophageal impedance,” “multichannel intraluminal impedance,” “impedance manometry,” and “high-resolution impedance manometry.”
Validation of impedance measurements to assess esophageal bolus transit
In the early 1990s, Silny at the Helmholtz Institute in Aachen, Germany, published a seminal paper describing MII as a novel technique to assesses intraluminal bolus movement by measuring changes in conductivity of the intraluminal content. This method exploits differences in electrical conductivity of the esophageal wall and its content when liquid or gas bolus passes by an pair of metal rings mounted on a catheter. The empty esophagus has a fairly stable baseline impedance of 1500 to 2000 Ohms. Subsequently, Blom and colleagues reported on the correlation of changes in intraluminal impedance with bolus movement during combined video fluoroscopy and impedance studies. When liquid passes by the impedance measuring segment, the following changes are observed ( Figs. 1 and 2 ):
- 1.
An initial drop in impedance when the liquid bolus enters the impedance-measuring segment, since this will enable the flow of electric current
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A low (nadir) impedance when the liquid bolus spans across both measurement rings
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A rise in impedance as the bolus is cleared from this segment by a peristaltic wave
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Return to baseline
In the early 2000s, Simren and colleagues further validated the ability of impedance to detect bolus movement. Considering bolus entry at a 50% drop in impedance from baseline to nadir and bolus exit at the recovery of impedance to the 50% value, Simren and colleagues found a strong correlation between video fluoroscopy and impedance for measuring the time of esophageal filling (r 2 = 0.89; P <.0001) and emptying (r 2 = 0.79; P <.0001).
MII classifies swallows as having complete bolus transit if the bolus enters the proximal site and exits (ie, there is a recovery of impedance above the 50% difference from baseline to nadir) from all distal impedance-measuring segments. Conversely bolus transit is defined as incomplete if impedance detects bolus retention in any of the distal channels (ie, channels situated below the transition zone). Bolus retention in the transition zone (ie, in the pressure nadir between the proximal striated and distal smooth muscles of the esophageal body) is considered acceptable (ie, not abnormal). Defining normal retention in the transition zone based on impedance measurements is difficult, because impedance cannot quantify the amount of bolus retained (ie, 1 mL or 10 mL will produce the same change in intraluminal impedance).
These definitions were confirmed by simultaneous barium impedance and manometry studies in a group of 15 normal volunteers. Imam and colleagues correlated impedance manometry findings with simultaneously recorded video fluoroscopic barium swallows in 15 normal volunteers (11 women, mean age 43 years). Fluoroscopy and impedance measurements correlated in 83 of 86 (97%) of swallows. Normal bolus transit was found in 61 of 83 swallows with normal contraction amplitude and complete bolus transit; stasis occurred in 7 of 83 swallows despite normal contraction amplitude in 4 of 7 swallows, and retrograde escape occurred in 14 of 83 swallows, allowing the authors to conclude that impedance monitoring is a valid transit test and describe bolus transit patterns in normal subjects for comparison with patients with esophageal motility disorders.
More recently, Cho and colleagues reported on the results of concomitant multichannel intraluminal impedance and video fluoroscopy recordings in a group of 16 patients with dysphagia. This group included patients with normal manometry (N = 6), ineffective esophageal motility (N = 1), distal esophageal spasms (N = 2), and achalasia (N = 7). According to the previously mentioned impedance criteria 21 of 22 swallows with normal barium emptying showed complete transit (96%), and 31 of 32 swallows with severe stasis showed incomplete transit (97%), underscoring that impedance correctly identifies swallows with complete and incomplete bolus transit in different patient groups.
Conventional impedance manometry
Early in the development of combined impedance manometry, studies in healthy volunteers were performed in order to establish normal values for this method. In a multicenter study including 60 healthy volunteers, the author and colleagues evaluated bolus transit for liquid and viscous (semisolid) boluses. This allowed defining normal values for bolus presence time at various levels in the esophagus, total bolus transit time for liquids, and viscous swallows ( Table 1 ). Using the 90th to 95th percentiles, it was observed that normal individuals have a complete bolus transit (defined as bolus entrance in the proximal esophagus and bolus exit in all distal esophageal measuring sites) in at least 80% of liquid and in at least 70% of viscous swallows. Conversely, patients with more than 20% of swallows with incomplete bolus transit for liquid and more than 30% of swallows with incomplete bolus transit for viscous are considered to have abnormal bolus transit for liquid and viscous, respectively. These observations were subsequently confirmed by European and Asian studies in healthy individuals.
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