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Esophageal manometry is considered the gold standard for assessing esophageal motor function. Although conventional manometry has been widely used to evaluate esophageal motor function, this is not fully satisfactory for explaining esophageal symptoms. High-resolution manometry (HRM) is designed to overcome the limitations of conventional manometric systems with advanced technologies. A solid-state HRM assembly with 36 solid-state sensors spaced at 1 cm intervals (Sierra Scientific Instruments Inc., Los Angeles, CA, USA) has been widely used around the world. Calibration and post-study thermal correction should be performed at each test. The HRM assembly was passed transnasally and positioned to record from the hypopharynx to the stomach. After a 5 minutes resting period to assess basal sphincter pressure, 5 mL water swallows are obtained in a supine posture. The interpretation of HRM data is still being refined. Recently, the HRM Classification Working Group revised the Chicago classification based on a systematic analysis of motility patterns in 75 control subjects and 400 consecutive patients. The below will show you a summary of the new Chicago classification of distal esophageal motility disorders to provide a practical way of interpreting HRM.
It is still not established how to interpret HRM data. Some clinicians have analyzed HRM data as conventional line tracings by transforming the pressure topography displays back to conventional line tracings. Recently, the new Chicago classification based on pressure topography was presented to enhance the strengths of the new technology. Typical swallow pressure topography is depicted in Figure 1.
The HRM Classification Working Group1 proposed a stepwise high-resolution esophageal pressure topography (HREPT) analysis algorithm. First, patients are characterized by esophagogastric junction (EGJ) pressure morphology (presence of hiatus hernia) and the presence or absence of impaired deglutitive EGJ relaxation. Second, each swallow is further categorized by the characteristics of the distal esophageal contraction (Table 1).1 These measures can now be made with analysis tools available in the current version of ManoViewTM analysis software (version 2.1; Sierra Scientific Instruments Inc.) and Solar GI HRM (Medical Measurement Systems, Enschede, Netherlands). Following the analysis of individual swallows based on the criteria in Table 1, the component results are synthesized into a global diagnosis by the Chicago classification of the distal esophageal motility disorders (Table 2).1
Many factors can affect deglutitive EGJ relaxation, including crural diaphragm (CD) contractions during respiration, deglutitive esophageal shortening, hiatal hernia, intrabolus pressure (IBP) within the EGJ, sphincter radial asymmetry, and movement of the recording sensor relative to the EGJ.2 These difficulties can be greatly improved with HREPT.3 Pressure topography plotting defines accurate localization of the EGJ and the deglutitive relaxation window. The integrated relaxation pressure (IRP) is the lowest average pressure for four contiguous or non-contiguous seconds within the relaxation window. The IRP is the optimal measure for quantifying deglutitive relaxation, with normal being defined as less than 15 mmHg.4
It has become possible to measure the sphincteric contribution of the CD and LES, and the relative localization of the LES and CD elements using HRM. Characterization of EGJ morphology can be performed using a computer program (MatlabTM, The MathWorks Inc., Natick, MA, USA) customized for processing binary manometric data into isobaric contour pressure plots and spatial pressure variation plots which is not widely available yet.5 EGJ morphology can be classified into three types6; type I is characterized by complete overlap of the CD and the LES. The respiratory inversion point (RIP) lies at the proximal margin of the EGJ. Type II is characterized by minimal, but discernible, LES-CD separation, however the nadir pressure between the LES and CD is still greater than gastric pressure. The RIP is within the EGJ at the proximal margin of the CD. Type III indicates the presence of hiatus hernia. Two subtypes are discernible, IIIa and IIIb, with the distinction being that the RIP is proximal to the CD in IIIa and proximal to the LES in IIIb. The shift in RIP is likely indicative of a grossly patulous hiatus, open throughout the respiratory cycle.
Following the analysis of the EGJ, an individual swallow is further categorized by the characteristics of the distal esophageal contraction. A pressure topography plot highlighting the 30 mmHg isobaric contour is generated, and then contractile front velocity (CFV) is calculated based on the 30 mmHg isobaric contour plots. Next step is to categorize each swallow into normal, hypotensive, and absent peristalsis. Finally, the distal esophageal contraction is further characterized by the vigour of contraction using a newly developed measure, the distal contractile integral (DCI).
Based on the 30 mmHg isobaric contour, each swallow is characterized as normal (intact 30 mmHg isobaric contour and a CFV < 8 cm/sec), hypotensive (≥ 3 cm defect in the 30 mmHg isobaric contour), or absent peristalsis (complete failure of contraction with no pressure domain above 30 mmHg) (Table 1).2
Following the analysis of individual swallows, total 10 swallows are classified into three categories: (i) ≥ 70% normal peristaltic contractions is normal, (ii) 100% of swallows with absent peristalsis constitutes absent peristalsis, and (iii) ≥ 70% of swallows with hypotensive peristaltic defects constitutes frequent hypotensive peristalsis (Table 2).2 It is notable that the Chicago group abandoned terminology such as peristaltic dysfunction and ineffective esophageal motility. These are not specific enough to describe a hypotensive peristaltic event and could easily include spasm and absent peristalsis.
Once swallows are characterized by the integrity of deglutitive EGJ relaxation and normality of the CFV, the distal esophageal contraction is further characterized for the vigour of contraction using DCI. The DCI integrates the length, contractile vigour, and duration of contraction of the first two sub-segments of the distal esophageal segment contraction, expressed as mmHg/sec·cm.4 A DCI value greater than 5,000 mmHg/sec·cm is considered elevated from an analysis of 75 normal subjects.4 Hypertensive peristalsis is consistent with nutcracker esophagus from conventional manometry. Spastic nutcracker defined by a higher threshold DCI (> 8,000 mmHg/sec.cm), is very rare, found in only 12 (3%) of 400 patient series.7 Interestingly, spastic nutcracker is clinically discernible by the uniform association with dysphagia or chest pain.7
It is obvious that performing the test using HRM is more convenient and informs us more data in comparison to the conventional manometry. Although the Chicago classification is an epochal way to understand esophageal motility disorders using HRM data, the validity of the new Chicago classification must be examined by future studies. And the factors considering this new technology should be discussed in terms of performing HRM and interpreting HRM data.
The author thanks Jin-A Park for her assitance in preparing the manuscript.
Financial support: None.
Conflicts of interest: None.