of the HRM catheter), potentially clarifying pressure artifacts that can erroneously elevate the IRP; i.e. an elevated IRP in both the supine and upright postures supports EGJ outflow obstruction, while an elevated IRP in only one position suggests artifactual IRP elevation [78].
Multiple rapid swallows involve performing five successive 2 ml liquid swallows at 2–3 s intervals to assess “contractile reserve” and the integrity of deglutitive inhibition (Figure 8.8). The normal response to multiple rapid swallows is persistent deglutitive inhibition until after the final swallow in the sequence. This accentuates LES relaxation and is then followed by a robust contraction in the esophageal body after the final swallow (contractile reserve) [58, 79]. Adequate contractile reserve is defined as augmentation of the esophageal contractile vigor following multiple rapid swallows (compared to a single supine 5 ml liquid swallow) and has been reported to be associated with a reduced risk for dysphagia after fundoplication and reduced susceptibility to GERD [58, 80, 81].
The rapid‐drink challenge test (sometimes referred to as multiple water swallows) involves rapidly drinking 200 ml of liquid [82–84]. A similar physiologic response is expected during rapid drinking as with multiple rapid swallows, i.e. profound deglutitive LES inhibition, deglutitive inhibition of esophageal body contractions, and a terminal‐augmented contractile response (Figure 8.8). However, distinguishing it from multiple rapid swallows, the greatest yield of the rapid drink challenge appears related to assessment of EGJ outflow obstruction. Normative values from two sizable cohorts have been reported, and an IRP during rapid drink challenge of ≥ 12 mmHg (using a Sierra‐vintage HRM assembly) was proposed as a threshold to identify EGJ dysfunction associated with achalasia, and ≥ 8 mmHg to identify “all cause” EGJ outflow obstruction [84, 85]. Additionally, the demonstration of panesophageal pressurization during the rapid drink challenge test may be indicative of achalasia or EGJ outflow obstruction [84, 86]. Esophageal clearance of the 200 cc liquid can also be assessed when HRIM is utilized. Monitoring the post‐swallow response for 30 s is often reported [82, 84, 87], or for up to 5 min to measure impedance bolus height, similar to a barium column height on a timed barium esophagram [71].
Figure 8.8 Multiple rapid swallows (MRS) and rapid drink challenge (RDC). Examples of an MRS (A) and RDC (B) from a healthy control. (A) The peristaltic contraction following the MRS sequence shows appropriate contractile augmentation, i.e. contractile reserve. The average DCI among the standard 5 ml liquid supine swallows was 4000 mmHg•s•cm. (C) MRS from a patient with gastroesophageal reflux disease showing absent contractile reserve with a failed swallow following the MRS. In (B), profound relaxation of the lower esophageal sphincter is observed in a healthy control with an integrated relaxation pressure (IRP) of 0 mmHg. In (D), a RDC from a patient with EGJ outflow obstruction by the Chicago Classification who was suspected of having achalasia demonstrates findings consistent with an EGJ outflow obstruction with an elevated IRP and panesophageal pressurization during the RDC.
Source: Used with permission from the Esophageal Center at Northwestern University.
Viscous test swallows, solid test swallows, and a solid test meal have also been applied, with the reasoning that these bolus types more closely simulate the real‐life scenario than single small‐volume liquid swallows and increase the potential for symptom elicitation during the manometry test. Viscous and solid test boluses increase intrabolus pressures and related EGJ outflow pressures, giving them their greatest yield in detecting EGJ outflow obstruction [8, 88, 89]. Further, utilization of a standardized, solid test meal has been reported (English “pasty” or 200 g of soft rice meal). The IRP and contractile parameters such as the DCI and distal latency can be assessed during test meal swallows to assess for EGJ outlfow obstruction, hypercontractility, hypocontractility, and spastic contractions [90–92]. An IRP threshold of > 25 mmHg during the standardized test meal (using a Sierra‐vintage catheter) has been proposed as the threshold with which to identify EGJ outflow obstruction [90, 92, 93]. Symptoms were also reproduced during the standardized test meal, leaving open the possibility of symptom association with abnormal motility to support the clinical relevance of the finding [93].
Overall, provocative maneuvers during HRM studies should be viewed as complementary rather than competitive to the standard, supine liquid swallow protocol that forms the basis of Chicago Classification diagnoses. Isolated abnormalities observed only with provocative tests may have uncertain clinical significance and should be interpreted with caution until their significance is demonstrated in longitudinal clinical outcome studies.
Conclusions
HRM and EPT provide for a detailed evaluation of esophageal motor function, facilitated by objective metrics applied for interpretation guided by a consensus‐generated classification scheme, the Chicago Classification. The standardized performance of HRM testing allows for reliable application of the Chicago Classification and generalization among clinical practices. Application of adjunct and provocative HRM maneuvers and potential incorporation of impedance with associated novel parameters may enhance future iterations of this scheme. However, such refinements of HRM/EPT analysis should be judged by their ability to detect specific clinical esophageal motility phenotypes directing specific clinical management strategies.
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