The first manometry system was developed by Jerry Dodds and Ron Wyle Arndorfer in 1970. Twenty years later, Ray Clouse developed what is now know as high-resolution manometry, increasing the number of sensors and decreasing the space between them on the pressure catheter to 1 cm.
HRM provides a complete temporal and spatial representation of the motor function of the esophagus. The presentation of the pressure data with colors and esophageal pressures through topography made new classifications of esophageal motor patterns possible, with the Chicago classification being the main one.
HRM displays the resting pressure of the sphincter and esophageal motor activity triggered by swallowing. The study consists of several phases:
- Evaluation of the resting pressures of the Upper Esophageal Sphincter (UES) and Lower Esophageal Sphincter (LES).
- Determine the topography of the esophageal pressure to define different esophageal motility disorders.
- Evaluation of the contractile force.
Evaluation of the UES and LES
The resting pressures of UES and LES are identified as two areas with increased pressure (color changes in the esophageal topography). HRM allows the differentiation of the basal pressure of the LES from contractions of the diaphragm. These two pressure zones should coincide: if they are separated, it indicates an herniated diaphragm.
The pressure inversion point (PIP) is the point where the negative pressure of the thoracic cavity changes to positive pressure generated by intragastric pressure. This point indicates the division between chest and abdomen created by the diaphragm. PIP is of vital importance to identify hiatal hernias. It is normally located immediately above the proximal edge of the LES.
LES relaxation is measured using the integrated relaxation pressure (IRP). The IRP is the lowest average pressure in the esophagogastric junction (EGJ) during 4 of the 10 seconds. A IRP higher than 15 mmHg indicates an increased resistance to bolus transit in the EGJ and is considered as pathological (achalasia, outflow tract obstruction such as neoplasia, strictures or complications of GERD).
Evaluation the peristaltic activity
The minimum pressure required for the transit of the bolus is 20 mmHg. Short (2 – 5 cm) or long (> 5 cm) areas of pressure under 20 mmHg are considered to be peristaltic defects. These are more significant if they occur in the distal esophagus.
The contractile deceleration point (CDP) is defined as the point in which the peristaltic wave slows. It is located near the LES and is associated with the point of maximum axial contraction. This is the point in which the peristaltic wave ends and the LES descends into its resting position.
The propagation of the peristaltic wave is determined by the distal latency (DL). It indicates whether the contraction is premature or whether there is any alteration in wave propagation. The DL is obtained from the interval between the start of the UES relaxation and the CDP. Its lower limit is 4.5 seconds.
The speed of the wave is measured using the contractile front velocity (CFV), which should not exceed 9 cm/second.
Evaluation of the contractile force
The measurement of the contractile force of the esophagus is defined as the distal contractile integral (DCI) and is generated on basis of smooth muscle contraction, contraction duration and distance of wave propagation. Its normal value is < 5000 mmHg/cm/second.
Abnormally high intrabolus pressure (IBP) may be secondary to outflow obstruction or decreased compliance of the esophageal wall. It is identified by a zone of constant isobaric pressure of variable length.
The Chicago Classification
The Chicago Classification is used to classify the esophageal motor disorders. This classification divides esophageal motor abnormalities into four groups:
- Esophageal obstruction.
- Abnormal esophageal motor function.
- Borderline esophageal motor function.
The following image illustrates the diagnostic algorithm of esophageal motor disorders. A lecture on the diagnosis and treatment of esophageal motor disorders will be published in the following weeks.
High-resolution manometry is the gold standard for the diagnosis of esophageal motor disorders, providing a complete temporal and spatial representation of the motor function of the esophagus. It makes it possible to evaluate the pressure of the upper esophageal sphincter, the lower esophageal sphincter, the peristaltic activity and the contractile force of the esophagus. Being able to interpret the results of a HRM is fundamental for the Upper Gastrointestinal Surgeon, as the Chicago Classification used for the diagnosis of esophageal motor disorders relies on the findings of HRM.