Muscle Shortening Along the Normal Esophagus During Swallowing

Abstract

Longitudinal shortening of the esophagus during peristaltic contraction has been previously analyzed globally using spaced mucosal clips. This method gives a relatively crude measurement. In this study, local longitudinal shortening (LLS) was evaluated using simultaneous high-resolution endoluminal ultrasound (HREUS) and manometry based on basic principles of muscle mechanics. We sought to determine if there are regional differences in LLS of the esophageal muscle during swallow-induced peristaltic contraction and evaluate shortening of the circular smooth muscle (CSM) and longitudinal smooth muscle (LSM) of the esophagus. Twenty normal subjects underwent simultaneous HREUS/manometry at 4 levels (5, 10, 15, and 20 cm above the upper border of the lower esophageal sphincter [LES] high-pressure zone) in the esophagus with 5-mL swallows of water. Ultrasound images were recorded with synchronized manometric pressure data. The images were digitized and the cross-sectional surface area (CSA) of the LSM, CSM, and total muscle (TM) were measured at baseline (at rest) and at peak intraluminal pressure (implying peak CSM contraction) during swallowing. LLS was calculated for the CSM and LSM using the principle of mass conservation, whereby the change in CSA relative to the resting CSA is quantitatively equal to the relative change in length of a local longitudinal muscle segment.CSM, LSM, and TM all shortened longitudinally, with the circular muscle shortening more than the longitudinal muscle, LLS of the CSM and TM layers at 5 cm above the LES was significantly greater than at 20 cm (CSM: 30% difference, P < .001; TM: 18% difference, P < .05). The greater shortening of LSM at 5 versus 20 cm was found not to be statistically significant (11% difference, P > .05). Peak intraluminal pressure strongly correlated with peak muscle thickness of all layers at all levels (r = 0.96-0.98).LLS increases from the proximal to the distal esophagus during bolus transport. CSM and LSM both shorten longitudinally, with CSM shortening more than LSM. The increase in LLS increases the efficiency of peristaltic contraction and likely contributes to the axial displacement of the LES preceding hiatal opening and esophageal emptying.

Circular and longitudinal muscles shortening indicates sliding patterns during peristalsis and transient lower esophageal sphincter relaxation

“…Contrary to the above, findings of Dai et al (3) and our data show that this is not the case. Differential axial shortening of the CM and LM during peristalsis and TLESR indicates independent movement of the two layers, i.e., the two muscle layers slide relative to each other.…”

“…In summary, based on our work and that of Miller et al (3,16) it is clear that the two muscle layers generate two unique axial shortening patterns. We propose that these patterns may activate mechanosensitive inhibitory and excitatory motor neurons of the myenteric plexus to modulate relaxation and contraction of the two muscle layers.…”

“…Because the LM layer was assumed to be directed in the long axis of the esophagus, it was thought to cause axial shortening of the esophagus, resulting in increase in the muscle CSA of two layers, which assumes that the two layers are anchored to each other and if the LM contracts CM will move passively with it. Dai et al (3) observed that the change in CM thickness during peristaltic contraction was significantly greater than LM in the distal esophagus, which was explained on the basis of spiral morphology of CM (16). Because the spiral angle of CM is greater in the distal esophagus than in the proximal esophagus (measured only up to 10 cm), axial shortening due to CM contraction is greater in the distal than the proximal esophagus (3).…”

“…Axial esophageal shortening is generally thought to be caused by contraction of the LM layer. However, Miller and colleagues (3,16) showed that CM contraction also contributes to axial esophageal shortening because of the spiral morphology of CM in the distal esophagus. Gilbert et al (4) used diffusion tensor imaging and fiber tracking to show that CM fibers are arranged in spiral rather than circular fashion.…”

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

“…The muscle mass of the circular and longitudinal muscle layers is nearly the same. In the resting state, the circumferentially averaged thickness of the muscularis has been measured by various researchers as 1.1-1.4 mm in the esophageal body, and 1.9-2.4 mm in the abdominal esophagus near the junction with the gastric cardia [1][2][3][4][5][6] . The function of the circular muscle layer of the esophageal muscularis propria is clear.…”