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

Abstract

Esophageal axial shortening is caused by longitudinal muscle (LM) contraction, but circular muscle (CM) may also contribute to axial shortening because of its spiral morphology. The goal of our study was to show patterns of contraction of CM and LM layers during peristalsis and transient lower esophageal sphincter (LES) relaxation (TLESR). In rats, esophageal and LES morphology was assessed by histology and immunohistochemistry, and function with the use of piezo-electric crystals and manometry. Electrical stimulation of the vagus nerve was used to induce esophageal contractions. In 18 healthy subjects, manometry and high frequency intraluminal ultrasound imaging during swallow-induced esophageal contractions and TLESR were evaluated. CM and LM thicknesses were measured (40 swallows and 30 TLESRs) as markers of axial shortening, before and at peak contraction, as well as during TLESRs. Animal studies revealed muscular connections between the LM and CM layers of the LES but not in the esophagus. During vagal stimulated esophageal contraction there was relative movement between the LM and CM. Human studies show that LM-to-CM (LM/CM) thickness ratio at baseline was 1. At the peak of swallow-induced contraction LM/CM ratio decreased significantly (Ͻ1), whereas the reverse was the case during TLESR (Ͼ2). The pattern of contraction of CM and LM suggests sliding of the two muscles. Furthermore, the sliding patterns are in the opposite direction during peristalsis and TLESR. muscularis propria; gastroesophageal reflux; unequal shortening of muscle layers THE ESOPHAGUS IS A RELATIVELY straight tube with simple functions, to transfer swallowed contents either from the mouth to the stomach or from the stomach toward the mouth as happens during vomiting, belching, and reflux. Prior studies have shown two distinct motor patterns in the esophagus: peristalsis that transports the swallowed contents aborally and transient lower esophageal sphincter (LES) relaxation (TLESR) that allows gastric contents to move into the esophagus toward the mouth. Inner circular muscle (CM) and outer longitudinal muscle (LM) layers play a key role in both oral and aboral movements of the bolus. Studies show that during peristalsis CM and LM contract together cranial to the bolus (ascending contraction), to propel the bolus in the aboral direction, and they relax together around and caudal to the bolus (descending relaxation) (11), to receive the bolus. On the other hand, during TLESR, a unique LM contraction that starts in the distal esophagus and progresses in the cranial direction is observed (1, 15). There is no significant contraction of the CM during TLESR.Axial stretch of esophagus in the oral direction activates neurologically mediated LES relaxation and possibly descending relaxation of the esophagus (7). Therefore, it is hypothesized that longitudinal muscle contraction related axial stretch is of fundamental importance in the descending relaxation of the peristaltic reflex. Axial esophageal shortening is generally thought to be caused b...

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