The aims of this study were to relate OPT to bolus transit and to establish the significance of CDP in accurately measuring peristaltic velocity. Concurrent fluoroscopy and HRM was used to correlate OPT patterns with localization of the swallowed bolus and fluoroscopically defined milestones of bolus transit. Our findings demonstrate that advance of the contractile front through the distal oesophageal segment is associated with two distinct domains with significantly different velocities. The observed shift in velocity did not occur at the pressure trough previously described between segments 2 and 3.12
Rather, the CDP occurred within S3 and correlated closely with the transition from peristaltic clearance to phrenic ampullary emptying. The importance of defining these phases of bolus emptying is that they occur by distinct mechanisms and, hence, are subject to distinct pathologies.
Rapid peristaltic propagation is a defining criterion for distal oesophageal spasm in conventional manometric classification.13,14
However, no convention exists on how or where to quantify peristaltic propagation. This study demonstrates that when assessed in OPT terms, CFV is not uniform and, in fact, in its later phase, has little to do with peristalsis. Rather, the measure defined as CFVfast
( and ) is most reflective of the neuromuscular transduction of peristalsis as in this region there are minimal confounding influences of IBP or oesophageal shortening. A consequence of this, evident in , is that the normative range for CFVfast
extend beyond the upper limit of normal for peristaltic velocity reported in conventional manometry studies (2 to 8 cm s−1
to 9.1 cm s−1
(supine swallows) or 12.7 cm s−1
(upright swallows). Although the specifics remain to be defined, this will necessarily impact on the definition and identification of distal oesophageal spasm in OPT terms.
Peristalsis consists of both longitudinal and circular muscle contraction and as peristalsis reaches the distal contractile segments (S3 and S4), luminal closure is achieved with the oesophagus still in a shortened state as a consequence of longitudinal muscle contraction.9
Fluoroscopically, the termination of peristalsis in the distal oesophagus is associated with transformation of the bolus cavity from the appearance of a pencil point to the globular form of the phrenic ampulla (see images of T3 and T4 in ). Emptying of the ampulla occurs with reduction of what amounts to physiological herniation, dependent upon sustained closure of the lumen above and the elastic recoil of the phrenoesophageal ligament restoring the LOS (S4) to its native position within the hiatus. The velocity at which this occurs, defined as CFVslow
is significantly less than peristaltic propagation (). This difference in clearance velocity between the oesophagus and phrenic ampulla was previously reported in an investigation that utilized concurrent manometry and fluoroscopy.9
However, the current investigation represents the first validation of a manometric algorithm to differentiate the two based solely on OPT characteristics. Variability in CFVslow
among individuals is likely dependent upon either an abnormally sustained peristaltic contraction or anatomical factors such as OGJ obstruction, laxity of the phrenoesophageal membrane or early hiatus hernia. With a well-defined, persistent hiatal hernia it may not be possible to measure CFVslow
as trans-hiatal emptying would be incomplete.
In summary, we utilized concurrent OPT/fluoroscopy studies to validate OPT paradigms for quantifying peristaltic velocity and the progression of phrenic ampullary emptying. A major observation was that the deceleration point in the CFV, occurring during the contraction of the distal smooth muscle oesophagus, was indicative of the transition from peristaltic clearance to formation and emptying of the phrenic ampulla. Additionally, this anatomic landmark can be easily identified using either a simple visual assessment or a more objective technique utilizing intersecting tangent lines along the CFVfast and CFVslow (). The description of these OPT landmarks will likely facilitate a furthering of our understanding of disorders of peristalsis, especially distal oesophageal spasm. We suspect that restricting the CFV measurement to the domain that is reflective of peristaltic clearance will alter the definition of distal oesophageal spasm as normal values of CFVfast can be greater than 10 cm s−1 in the upright posture. Furthermore, identification of the CFVslow domain as a correlate of phrenic ampullary emptying may prove helpful in understanding abnormal mechanics and bolus transit in the context of OGJ abnormalities.