Function of longitudinal vs circular muscle fibers in esophageal peristalsis, deduced with mathematical modeling

We summarize from previous works the functions of circular vs. longitudinal muscle in esophageal peristaltic bolus transport using a mix of experimental data, the conservation laws of mechanics and mathematical modeling. Whereas circular muscle tone generates radial closure pressure to create a local peristaltic closure wave, longitudinal muscle tone has two functions, one physiological with mechanical implications, and one purely mechanical. Each of these functions independently reduces the tension of individual circular muscle fibers to maintain closure as a consequence of shortening of longitudinal muscle locally coordinated with increasing circular muscle tone. The physiological function is deduced by combining basic laws of mechanics with concurrent measurements of intraluminal pressure from manometry, and changes in cross sectional muscle area from endoluminal ultrasound from which local longitudinal shortening (LLS) can be accurately obtained. The purely mechanical function of LLS was discovered from mathematical modeling of peristaltic esophageal transport with the axial wall motion generated by LLS. Physiologically, LLS concentrates circular muscle fibers where closure pressure is highest. However, the mechanical function of LLS is to reduce the level of pressure required to maintain closure. The combined physiological and mechanical consequences of LLS are to reduce circular muscle fiber tension and power by as much as 1/10 what would be requiredfor peristalsis without the longitudinal muscle layer, a tremendous benefit that may explain the existence of longitudinal muscle fiber in the gut. We also review what is understood of the role of longitudinal muscle in esophageal emptying, reflux and pathology.

Circular smooth muscle contributes to esophageal shortening during peristalsis

AIM:To study the angle between the circular smooth muscle(CSM) and longitudinal smooth muscle(LSM) fibers in the distal esophagus.METHODS:In order to identify possible mechanisms for greater shortening in the distal compared to proximal esophagus during peristalsis,the angles between the LSM and CSM layers were measured in 9 cadavers.The outer longitudinal layer of the muscularis propria was exposed after stripping the outer serosa.The inner circular layer of the muscularis propria was then revealed after dissection of the esophageal mucosa and the underlying muscularis mucosa.Photographs of each specimen were taken with half of the open esophagus folded back showing both the outer longitudinal and inner circular muscle layers.Angles were measured every one cm for 10 cm proximal to the squamocolumnar junction(SCJ) by two independent investigators.Two human esophagi were obtained from organ transplant donors and the angles between the circular and longitudinal smooth muscle layers were measured using micro-computed tomography(micro CT) and Image J software.RESULTS:All data are presented as mean ± SE.The CSM to LSM angle at the SCJ and 1 cm proximal to SCJ on the autopsy specimens was 69.3 ± 4.62 degrees vs 74.9 ± 3.09 degrees,P = 0.32.The CSM to LSM angle at SCJ were statistically significantly lower than at 2,3,4 and 5 cm proximal to the SCJ,69.3 ± 4.62 degrees vs 82.58 ± 1.34 degrees,84.04 ± 1.64 degrees,84.87 ± 1.04 degrees and 83.72 ± 1.42 degrees,P = 0.013,P = 0.008,P = 0.004,P = 0.009 respectively.The CSM to LSM angle at SCJ was also statistically significantly lower than the angles at 6,7 and 8 cm proximal to the SCJ,69.3 ± 4.62 degrees vs 80.18 ± 2.09 degrees,81.81 ± 1.75 degrees and 80.96 ± 2.04 degrees,P = 0.05,P = 0.02,P = 0.03 respectively.The CSM to LSM angle at 1 cm proximal to SCJ was statistically significantly lower than at 3,4 and 5 cm proximal to the SCJ,74.94 ± 3.09 degrees vs 84.04 ± 1.64 degrees,84.87 ± 1.04 degrees and 83.72 ± 1.42 degrees,P = 0.019,P = 0.008,P = 0.02 respectively.At 10 cm above SCJ the angle was 80.06 ± 2.13 degrees which is close to being perpendicular but less than 90 degrees.The CSM to LSM angles measured on virtual dissection of the esophagus and the stomach on micro CT at the SCJ and 1 cm proximal to the SCJ were 48.39 ± 0.72 degrees and 50.81 ± 1.59 degrees.Rather than the angle of the CSM and LSM being perpendicular in the esophagus we found an acute angulation between these two muscle groups throughout the lower 10 cm of the esophagus.CONCLUSION:The oblique angulation of the CSM may contribute to the significantly greater shortening of distal esophagus when compared to the mid and proximal esophagus during peristalsis.

Ileocecal valve dysfunction in small intestinal bacterial overgrowth: A pilot study

AIM: To explore whether patients with a defective ileocecal valve (ICV)/cecal distension reflex have small intestinal bacterial overgrowth. METHODS: Using a colonoscope, under conscious sedation, the ICV was intubated and the colonoscope was placed within the terminal ileum (TI). A manometry catheter with 4 pressure channels, spaced 1 cm apart, was passed through the biopsy channel of the colonoscope into the TI. The colonoscope was slowly withdrawn from the TI while the manometry catheter was advanced. The catheter was placed across the ICV so that at least one pressure port was within the TI, ICV and the cecum respectively. Pressures were continuously measured during air insufflation into the cecum, under direct endoscopic visualization, in 19 volunteers. Air was insufflated to a maximum of 40 mmHg to prevent barotrauma. All subjects underwent lactulose breath testing one month after the colonoscopy. The results of the breath tests were compared with the results of the pressures within the ICV during air insufflation. RESULTS: Nineteen subjects underwent colonoscopy with measurements of the ICV pressures after intubation of the ICV with a colonoscope. Initial baseline readings showed no statistical difference in the pressures of the TI and ICV, between subjects with positive lactulose breath tests and normal lactulose breath tests. The average peak ICV pressure during air insufflation into the cecum in subjects with normal lactu-lose breath tests was significantly higher than cecal pressures during air insufflation (49.33 ± 7.99 mmHg vs 16.40 ± 2.14 mmHg, P = 0.0011). The average percentage difference of the area under the pressure curve of the ICV from the cecum during air insufflations in subjects with normal lactulose breath tests was significantly higher (280.72% ± 43.29% vs 100% ± 0%, P = 0.0006). The average peak ICV pressure during air insufflation into the cecum in subjects with positive lactulose breath tests was not significantly different than cecal pressures during air insufflation 21.23 ± 3.52 mmHg vs 16.10 ± 3.39 mmHg. The average percentage difference of the area under the pressure curve of the ICV from the cecum during air insufflation was not significantly different 101.08% ± 7.96% vs 100% ± 0%. The total symptom score for subjects with normal lactulose breath tests and subjects with positive lactu-lose breath tests was not statistically different (13.30 ± 4.09 vs 24.14 ± 6.58). The ICV peak pressures during air insufflations were significantly higher in subjects with normal lactulose breath tests than in subjects with positive lactulose breath tests (P = 0.005). The average percent difference of the area under the pressure curve in the ICV from cecum was significantly higher in subjects with normal lactulose breath tests than in subjects with positive lactulose breath tests (P = 0.0012). Individuals with positive lactulose breath tests demonstrated symptom scores which were significantly higher for the following symptoms: not able to finish normal sized meal, feeling excessively full after meals, loss of appetite and bloating. CONCLUSION: Compared to normal, subjects with a positive lactulose breath test have a defective ICV cecal distension reflex. These subjects also more commonly have higher symptom scores.