rel="nofollow" href="#ulink_7395a136-22f3-529b-9e67-bcf639f357e1">Figure 8.2 Esophageal pressure topography metrics. (A) An example of a normal swallow with intact peristalsis; (B) a swallow associated with esophagogastric junction (EGJ) outflow obstruction. Deglutitive lower esophageal sphincter relaxation is measured by the integrated relaxation pressure (IRP); the borders of the EGJ incorporated into the IRP measures are signified by the dashed orange lines. The contractile deceleration point (CDP; red star) is located by identifying the inflection point in propagation velocity along the 30 mmHg isobaric contour; in the setting of compartmentalized pressurization (B; identified by white *), the CDP is identified along an isobaric contour of greater pressure than the intrabolus pressurization. The distal latency is measured as the time from the onset of swallow to the CDP. Peristaltic vigor is measured by the distal contractile integral (DCI).
Source: Used with permission from the Esophageal Center at Northwestern University.
The assessment of basal EGJ characteristics and function carries clinical significance with regard to gastroesophageal reflux susceptibility; greater LES‐CD separation (type III morphology), reduced CD augmentation pressures, and low EGJ‐CI (generally <30 mmHg•cm) are associated with increased reflux as measured by pH‐metry or pH/impedance‐metry [25, 27–31]. Elevated basal EGJ pressures are also observed (a hypertensive LES), but the clinical relevance of this finding remains unclear [32].
Step 2: Apply HRM metrics to individual swallows
Interpretation of an HRM study is aided by several quantifiable metrics and patterns that can be assessed by analysis software after appropriate placement of manometric landmarks by an interpreter. These include the IRP, DCI, and distal latency (DL) (Figure 8.2):
The IRP is the measure of deglutitive EGJ relaxation and is the primary metric to define an EGJ outflow obstruction. The IRP is calculated as the mean of the 4 s (contiguous or noncontiguous) of the lowest pressure at the EGJ during a 10 s window following the swallow and referenced to gastric pressure [33, 34]. The axial borders of the IRP measurement window should span the length of the EGJ, including swallow‐associated esophageal shortening, if observed. Because the IRP is referenced to gastric pressure, proper placement of the gastric reference is important, typically placed 2 cm below the distal border of the EGJ. However, placement should be adjusted if there appears to be a pressure artifact.
The DCI is a measure of peristaltic (contractile) vigor and calculated as the pressure amplitude x duration x axial length (mmHg•s•cm) of the distal esophageal contraction proximal to the EGJ and referenced to 20 mmHg so as to exclude pressure artifacts [3, 35]. The DCI is the primary determinant of hypercontractile swallows (high DCI) as well as weak and failed peristalsis (low DCI) [3, 4, 36, 37].
The DL reflects the duration of deglutitive inhibition of the distal esophageal contraction and is used to define “spastic” or premature contractions [4, 38, 39]. The DL is the time interval (seconds) from the onset of the swallow (as noted by the relaxation of the UES) to the contractile deceleration point (CDP) [39, 40]. The CDP is the most distal inflection point in the velocity of the peristaltic wavefront (localized on the 20 mmHg isobaric contour within 3 cm of the EGJ) [41]. If compartmentalized pressurization (Figure 8.3B) is present, the CDP should be localized on an isobaric pressure contour set to be greater than the pressure within the zone of compartmentalized pressurization.Figure 8.3 Stepwise classification of individual swallows on HRM/EPT. Application of EPT metrics provides a scheme with which to classify individual swallow types. Specific swallow types are identified in dark purple boxes.Contractile front velocity: The velocity (cm/s) of the contractile front can also be measured; rapid contractions are sometimes considered simultaneous or “spastic” contractions. However, owing to concerns about the specificity and variability of this measure, the Chicago Classification uses only the DL to define “spastic” contractions [4, 21, 39].
Peristaltic breaks: Using the isobaric contour tool set at 20 mmHg, the peristaltic wave is assessed for peristaltic breaks, or gaps in the isobaric contour. Breaks are considered significant if they are > 5 cm in axial length because these are associated with impaired bolus clearance as determined by HRIM.
Pressurization pattern: Pressurization of > 30 mmHg spanning from the UES to the EGJ is termed panesophageal pressurization and is the defining feature of type II achalasia (see below). Compartmentalized pressurization, i.e. pressurization between a progressing esophageal contraction and the EGJ (Figure 8.2B), may be indicative of esophageal outflow obstruction.
Step 3: Classify individual test swallows
In the next step of the hierarchical analysis, each swallow is classified, guided by the previous metrics [4] (Figures 8.3 and 8.4). Swallow types include:
Premature: DL less than the lower limit of normal, typically <4.5 s with a DCI > 450 mmHg•s•cm
Hypercontractile: DCI greater than the upper limit of normal (typically > 8000 mmHg•s•cm)
Failed: DCI < 100 mmHg•s•cm or DCI < 450 mmHg•s•cm with a distal latency < 4.5 s; also classified as an ineffective swallowFailed swallows with panesophageal pressurization
Weak: DCI 100–450 mmHg•s•cm; also classified as an ineffective swallow
Fragmented: DCI > 450 mmHg•s•cm with a large (> 5 cm) peristaltic break
Normal: Not meeting the previous criteria; hence DCI 450–8000 mmHg•s•cm without a large peristaltic break and DL ≥ 4.5 s
Figure 8.4 Swallow types of HRM/EPT. (A) Premature swallow; the distal latency (arrow) is 4 seconds. (B) Hypercontractile swallow: the distal contractile integral (DCI; white dashed box) was 28 000 mmHg•s•cm, and the distal latency was 6 seconds. (C) Failed swallow. (D) Weak swallow; DCI 400 mmHg•s•cm with only a small peristaltic break in the 20 mmHg isobaric contour. (E) Fragmented swallow; DCI 740 mmHg•s•cm with large (> 5 cm) peristaltic break. (F) Normal swallow.
Source: Used with permission from the Esophageal Center at Northwestern University.
Step 4: Step designation of an esophageal motility diagnosis
After all test swallows are classified, an esophageal motility diagnosis can be generated according to the Chicago Classification, which provides a hierarchical framework (Figure 8.5) [4]. Because peristalsis may be altered in response to EGJ outflow obstruction, the presence or absence of an EGJ outflow obstruction (median IRP exceeding the upper limit of normal) is the initial branch point in the diagnostic classification scheme. If EGJ outflow obstruction is associated with 100% failed or premature (spastic) swallows, a diagnosis of achalasia is achieved. Achalasia is then subclassified as type I, II, or III (Figure 8.6), which has both prognostic and treatment implications. Type II (with panesophageal pressurization) has the greatest likelihood of treatment success, while type III (spastic) has the lowest treatment success rate (Table 8.2) [42–45]. With respect to therapy, myotomy – particularly a calibrated endoscopic