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Esophageal motility disorders are classified as primary when they are one of a small number of isolated disorders of motility that include achalasia, diffuse esophageal spasm, nutcracker esophagus, and nonspecific esophageal motility disorders of the esophagus or as secondary when associated with known disease processes (Table 393-1). A basic understanding of normal esophageal motility allows appreciation of the diagnostic criteria for various motility disorders.

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Table 393-1. Esophageal Motility Disorders 
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The esophagus is a dynamic muscular conduit connecting the oropharynx to the stomach. Two sphincters, the upper esophageal sphincter (UES) and lower esophageal sphincter (LES), divide the esophagus from the oropharynx and stomach respectively. The esophagus is composed of striated muscle in the upper third and smooth muscle in the lower two thirds. Similar to the remainder of the gastrointestinal tract, the smooth muscle portions of the esophagus are divided into 2 layers: the innermost arranged in a circular pattern and the outer aligned along the longitudinal axis. Each layer is thought to perform a unique function. The circular muscle layer collapses the lumen of the esophagus and is responsible for generating contractile pressure, while the longitudinal layer shortens the esophagus and may play a role in opening the LES. The UES consists of C-shaped bundles of muscle fibers from the cricopharyngeus muscle. The LES consists of components from the esophagus, stomach, and skeletal muscle from the diaphragm. At rest, the pressure within the esophagus reflects the intrathoracic pressure and is therefore slightly negative during inspiration and slightly positive during expiration. Closure of the UES prevents swallowing of air, and closure of the LES prevents reflux of gastric contents during inspiration. The pressure that is tonically maintained by the UES varies tremendously, being almost absent during sleep and increasing to over 100 mm Hg with emotional stress, straining, or when the esophagus is distended or perfused with acid fluid. The LES maintains a pressure of approximately 20 mm Hg, with values below approximately 10 mm Hg being abnormal. LES pressure is augmented during inspiration by contraction of the diaphragm. The LES tone is decreased by anesthesia, morphine, diazepam, β-adrenergic agents, dopamine, secretin, cholecystokinin, glucagon, vasoactive inhibitory peptide, progesterone and estrogen, nitrites, nifedipine, theophylline, intraduodenal fat, ethanol, and nicotine. Relaxation of the LES appears to be mediated by the actions of vasoactive inhibitory peptide and/or nitric oxide.

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Coordination of the muscles of the pharynx, UES, esophagus, and LES are required for propulsion of food and liquid bolus to the stomach. Swallowing induces relaxation and opening of the UES to allow transfer of ...

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