Esophageal manometry is a diagnostic procedure used to measure the pressure and coordinated movement of the muscles within the esophagus. This test is performed when patients experience symptoms like difficulty swallowing, chest pain, or chronic acid reflux unresponsive to standard treatment. The goal is to assess the motor function, or motility, as the esophagus transports food and liquid to the stomach. Interpreting the manometry report requires familiarity with the specific areas measured and the quantitative metrics derived from the pressure readings.
What Esophageal Manometry Measures
The manometry test focuses on measuring the pressure dynamics across three main anatomical regions of the esophagus. At the top is the Upper Esophageal Sphincter (UES). The high-resolution manometry catheter records the pressure changes in this area immediately following a swallow.
The longest section is the Esophageal Body, where the main muscle contractions, known as peristalsis, propel the swallowed material downward. Manometry assesses the speed, strength, and coordination of these contractions. Abnormalities in this section can indicate issues with the propulsive force needed for effective swallowing.
At the junction with the stomach lies the Lower Esophageal Sphincter (LES), a band of muscle that acts like a valve. The LES must relax completely during a swallow to allow contents to pass, and then close tightly to prevent acid reflux. Measuring the pressure and relaxation capability of the LES is a primary function of the manometry test.
Essential Metrics for Interpretation
Interpreting the data relies on three quantitative metrics that summarize muscle activity. The Integrated Relaxation Pressure (IRP) focuses on the adequacy of Lower Esophageal Sphincter (LES) relaxation. It represents the lowest average pressure recorded across the esophagogastric junction over a four-second period after a swallow is initiated. A normal IRP is typically less than 15 mmHg; a value above this threshold suggests an obstruction or failure of the LES to fully open.
The vigor and strength of the peristaltic contraction in the esophageal body are quantified by the Distal Contractile Integral (DCI). This metric is a mathematical calculation that combines the amplitude, duration, and length of the pressure wave into a single number, expressed in units of mmHg·s·cm. A normal DCI typically falls between 450 and 8,000 mmHg·s·cm, indicating a contraction strong enough to effectively clear the esophagus. A DCI below 450 mmHg·s·cm signifies a weak or ineffective contraction, while a value exceeding 8,000 mmHg·s·cm points to hypercontractility, or excessive force.
The third measurement, Distal Latency (DL), assesses the timing and coordination of the muscle contraction. It measures the time interval from the moment the Upper Esophageal Sphincter relaxes to the point where the contraction wave slows down just before the LES. A normal DL is greater than 4.5 seconds, ensuring that the peristaltic wave reaches the sphincter at the correct time to push the material through. A Distal Latency shorter than 4.5 seconds indicates a premature or spastic contraction, meaning the muscle is firing too quickly and out of sync with the swallowing process.
Navigating the Chicago Classification System
Manometry results are not simply read as isolated numbers but are interpreted using a standardized framework called the Chicago Classification, currently in version 4.0. This classification system provides a hierarchical, step-by-step algorithm that clinicians use to move from a set of metrics to a definitive diagnosis. Its purpose is to standardize interpretation across different institutions and minimize diagnostic variability.
The process begins by first examining the Integrated Relaxation Pressure (IRP) to evaluate the function of the Lower Esophageal Sphincter. If the IRP is elevated, it immediately directs the analysis toward disorders involving outflow obstruction, such as achalasia. If the IRP is within the normal range, the focus shifts to evaluating the peristaltic function in the esophageal body using the Distal Contractile Integral (DCI) and Distal Latency (DL).
This classification system categorizes motility disorders based on the location of the dysfunction. The primary distinction is made between disorders of the esophagogastric junction, which involve the LES, and disorders of peristalsis, which affect the body of the esophagus. This systematic approach ensures that obstructive disorders are identified first, guiding the subsequent diagnostic pathway.
Understanding Common Motility Diagnoses
The Chicago Classification framework leads to the identification of several common motility disorders, each defined by a specific pattern of the manometric metrics. The most recognized is Achalasia, which is characterized by a consistently high IRP, reflecting a failure of the LES to relax properly. This finding is paired with the absence of effective peristalsis in the esophageal body.
Achalasia is further divided into three subtypes based on the pattern of pressure in the esophageal body. Type I Achalasia shows high IRP with completely absent muscle contractions, resulting in a flaccid esophagus. Type II is the most common subtype, presenting with a high IRP and episodes of pan-esophageal pressurization, where the entire esophagus pressurizes simultaneously without a coordinated wave.
Type III Achalasia, sometimes called spastic achalasia, also has a high IRP, but it is defined by premature or spastic contractions, indicated by a Distal Latency of less than 4.5 seconds in at least 20% of swallows.
Other disorders involve normal LES relaxation but abnormal peristalsis, such as Jackhammer Esophagus, also known as hypercontractile esophagus. This diagnosis is made when a patient has a normal IRP and Distal Latency, but the Distal Contractile Integral (DCI) is excessively high, exceeding 8,000 mmHg·s·cm in at least 20% of swallows.
In contrast, Ineffective Esophageal Motility (IEM) is defined by weak peristalsis, where the IRP is normal, but the DCI is low (below 450 mmHg·s·cm) in 50% or more of the test swallows. This indicates a reduced ability of the esophagus to effectively push food toward the stomach.