Lower Esophageal Sphincter Function in the Neonate

Abstract

After completing this article, readers should be able to: 1. Describe the functions of the lower esophageal sphincter. 2. Delineate the circumstances in which gastroesophageal reflux can occur in infants. 3. Explain the role of transient lower esophageal sphincter relaxation in neonatal gastroesophageal reflux. The lower esophageal sphincter (LES) is a region of smooth muscle thickening at the esophagogastric junction. The primary function of the LES is to control flow of luminal contents between the esophagus and stomach and to serve as a physical barrier against the occurrence of gastroesophageal reflux (GER) (ie, retrograde flow of gastric contents from the stomach into the esophagus). The LES is primarily controlled by parasympathetic (vagus) nerve pathways, which regulate contraction (predominantly cholinergic) and reflex relaxation (predominantly nonadrenergic noncholinergic). The LES is supported extrinsically by the crural diaphragm, which acts as an “external” sphincter. Basal LES pressure (LESP), which can be measured by passing a manometric catheter through the LES high-pressure zone, is generated by a combination of smooth muscle tone and the external compressive squeeze of the crural diaphragm. Measurements of LESP have shown that LES tone varies over time, depending on prandial state, and is influenced by many factors, including postprandial cholecystokinin release, the migratory motor complex, respiratory effort, straining, physical activity, and methylxanthine therapy. As such, the measurement of LESP at a single point in time may be poorly representative of the “true” LESP profile. The functioning of the LES as a competent antireflux barrier is very important to the developing neonate. GER occurs more frequently in the neonate than in older children and typically is recognized during episodes of regurgitation that are very common in infants. This “physiologic GER” or benign feeding-related regurgitation usually resolves spontaneously and is not necessarily symptomatic of GER disease. Pathologic GER (GER disease) may be suggested by reflux …