Fig. 6.1
Comparison of gastroesophageal and anorectal junctions. When the anorectal junction is graphically rotated (middle image), note the similarity in conformations of the rectum and the esophagus/stomach. In both instances, relaxation or contraction of the “sling” (i.e., the puborectalis and crural diaphragm) is able to facilitate or prevent flow, respectively. Modified from the original illustrations of Allison. Reprinted with permission from the Journal of the American College of Surgeons, formerly Surgery Gynecology & Obstetrics
At the intra-luminal portion of the esophagus at the angle of His, there is a ridge of tissue that appears to act as a “flap-valve” in helping to prevent GER. Hill et al. described this “flap-valve” and supported the concept by a study in which they measured the GEJ pressure gradient required to generate gastroesophageal flow in cadavers [1]. As there is no LES or CD contraction in cadavers, the measured pressure gradient suggested that a barrier to reflux flow must be generated by a functional “flap-valve.” The required pressure gradient was shown to augment with accentuation of the flap valve with sutures and also to be lower and often absent in cadavers with a HH. When a HH was present, a pressure gradient could be restored and/or increased with applying posterior fixation, which returned the GEJ to its intra-abdominal position.
Hill et al. further examined a group of GERD patients and normal controls and developed a grading system based on the endoscopic appearance of the GEJ (see Fig. 6.2). Flap-valve grades I and II were more common in normal controls and grades III and IV were more common in GERD patients. When applied prospectively, they showed that this grading scheme could accurately predict the GERD status of patients. Another study demonstrated that this flap-valve grading scheme was also associated with increased esophageal acid exposure during exercise, which causes intra-abdominal strain (flap-valve grades III and IV had greater acid exposure than grades I and II) [32]. Furthermore, these findings were shown to be independent of decreased LES pressure.
Fig. 6.2
Flap-valve grading system. Grade I—a normal, prominent ridge or fold of tissue at the lesser curvature, closely approximated to the endoscope; Grade II—fold present but with periodic opening and closing (often associated with respiration) around the endoscope; Grade III—fold not prominent and hiatus freely open, hiatal hernia may or may not be present; Grade IV—no fold, large hiatal hernia (i.e., axial displacement of the squamocolumnar junction) with open esophagus. Modified from Hill Gastrointest Endosc., 1996;44(5):541–7) with permission
The flap-valve concept nicely demonstrates how multiple components can interact to promote the anti-reflux barrier.
Reduce Gastric Reflux Flow and Volume
Poiseuille’s Law of Flow states that flow (F) is directly proportional to the pressure gradient (ΔP) multiplied by the radius (r) to the fourth power and is inversely proportional to the fluid viscosity (η) and length (ℒ) of the system (
). While this equation makes several assumptions of the system to which it applies, the concept remains apparent that the radius of the tube is the dominant variable of flow.
). While this equation makes several assumptions of the system to which it applies, the concept remains apparent that the radius of the tube is the dominant variable of flow.Given the relationship of opening dimensions to flow, it has been hypothesized that increased GEJ distensibility and dimensions would affect the volume of reflux in patients with GERD and HH. A series of studies using a trans-GEJ placed barostat and manometry device combined with concurrent fluoroscopy to measure the radial dimensions of the GEJ in response to low distension pressures were utilized to assess the radial dimensions of the GEJ in GERD [25, 33]. They found that patients with HH had greater relaxed GEJ distensibility, i.e., the GEJ opening occurred at lower pressures and opened wider for a given pressure, than in GER patients without HH and normal controls (Fig. 6.3). In addition, further examination using distension pressures just above and just below intragastric pressure demonstrated that only the group of patients with GER and HH (not GER without HH or normal controls) demonstrated GEJ opening at pressures below intragastric pressure [25].
Fig. 6.3
Radial dimensions of the GEJ in response to distension pressures. Increased compliance of the GEJ in patients with GERD +/− HH is demonstrated with the plotted measurements of GEJ opening diameters made from posteroanterior (PA) and lateral fluoroscopic projections in response to intra-hydrostat bag pressures (relative to gastric pressure). While radial asymmetry was seen in all three groups, the asymmetry is most pronounced in the normal patients due to the comparably increased PA diameters seen in the GERD HH (+) and GERD HH (−) groups. Modified from Pandolfino et al. Gastroenterology 2003;125(4):1018–24 with permission
An alternative method of measuring GEJ distension to the cumbersome hydrostat/fluoroscopy is an endoscopic functional luminal imaging probe (EndoFLIP; Crospon Inc. Galway, Ireland). The EndoFLIP is a device that utilizes impedance planimetry to measure intra-luminal cross-sectional area and thus when positioned across the GEJ and utilized with concurrent pressure measurements, can measure GEJ compliance. A study utilizing EndoFLIP compared the GEJ distensibility of normal controls with patients with GERD [34]. Patients also underwent endoscopy to assess the flap-valve grade. The study demonstrated that in all patients, the diaphragmatic hiatus was the least distensible region in both controls and GERD patients, but that the GEJ distensibility was greater in GERD patients than in normal controls. Interestingly, there was poor correlation between the FLIP-measured GEJ distensibility and the flap-valve grade. This demonstrates that there is radial, as well as axial, disruption that occurs at the hiatus. Given the relationship of flow with the opening diameter, a more distensible GEJ can facilitate the presence and volume of reflux.
While radius is the dominant variable in flow, length is inversely proportional to flow to a lesser degree. The lengths of the LES, the GEJ high-pressure zone, and the intra-abdominal esophagus are observed to be shorter in patients with HH [10, 26, 28, 29, 35]. The intra-abdominal esophagus is an area of the esophagus subject to increased external pressures of the intra-abdominal compartment and is a crucial component of the flap valve, as in-vitro demonstrations have shown increased gastroesophageal pressure gradients required to generate flow through longer intra-abdominal esophageal lengths [35]. Thus, shorter lengths of LES and intra-abdominal esophagus may further add a component of incompetence to the anti-reflux barrier when a HH is present.
Impaired Esophageal Acid Clearance and Re-reflux
Esophageal acid exposure is increased in the presence of a hiatal hernia, but is due to more than just the deficiencies in preventing reflux as described above. Not only is more reflux and acid able to cross the GEJ, but the esophagus’s ability to clear the acid is further impaired and occurs more slowly in patients with HH [36, 37]. A study utilizing concurrent videofluoroscopy and manometry to examine esophageal emptying in normal controls and patients with HH showed that complete esophageal emptying occurred less frequently in patients with HH [37]. In addition, they showed that whether or not the hernia reduced between swallows was a factor that appeared to have an effect on esophageal emptying and the timing of reflux from the hernia sac (patients with a hernia that completely reduced between swallows had more frequent complete esophageal clearance and their reflux from the hernia sac occurred early after LES relaxation, where as patients with a non-reducing HH were observed to have late flow).
Because of incompetence at the hiatus and the potential for re-reflux from fluid retained within the hernia sac, the environment of the proximal stomach is important in determining the make-up of the refluxate. A post-prandial “acid pocket” in the proximal stomach has been described that may allow for increased esophageal acid exposure during LES relaxation [38]. Using a pH catheter pull-through method, a “pocket” of acid was demonstrated to be present at the GEJ after meals, suggesting this acid pocket may not be subjected to the buffering effects of the meal.
In an elegant study performed by Beaumont et al. [39] the post-prandial acid pocket was examined in healthy volunteers (without GERD or HH), and patients with GERD with no or small (<3 cm) HH and large (>3 cm) HH. The “acid-pocket” was visualized with nuclear medicine imaging while LES relaxation, esophageal reflux, and pH were concurrently measured with esophageal manometry, impedance, and a pull-through pH catheter (Fig. 6.4). They observed that the post-prandial acid pocket remained below the GEJ in all the healthy volunteers and most (84 %) of those with GERD and small HH. However, in GERD patients with large HH, the acid pocket extended above the diaphragm for the entire duration of the study (2 h) in half of the patients and intermittently migrated above the diaphragm in 90 % of the patients. In addition, while all three groups of patients had a similar number of TLESRs, those with HH were more likely to have acidic reflux (large HH more likely than small). The position of the acid pocket above the diaphragm during a TLESR was more likely to lead to acidic reflux. Thus, patients with large HH and acid pocket about the diaphragm were observed to have more esophageal acid exposure. Multivariate regression analysis indicated that presence of HH and position of the acid pocket above the diaphragm were statistically significant risk factors for acidic reflux, while distance between the acid pocket and the squamocolumnar junction was protective against acidic reflux.
