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Esophageal motility disorders are classified as primary when they are 1 of a small number of isolated disorders of motility that include achalasia, esophagogastric junction (EGJ) outflow obstruction, major disorders of peristalsis, or minor disorders of peristalsis, or as secondary when associated with known disease processes (Table 388-1). A basic understanding of normal esophageal motility allows appreciation of the diagnostic criteria for various motility disorders. Of the primary esophageal motor disorders, achalasia of the lower esophageal sphincter is the most common and well recognized.
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PATHOGENESIS AND EPIDEMIOLOGY
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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), separate the esophagus from the oropharynx and the 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 layer is arranged in a circular pattern, and the outer layer is 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 maintained tonically by the UES varies tremendously, being almost absent during sleep and increasing to over 100 mmHg with emotional stress, when straining, or when the esophagus is distended or perfused with acid fluid. The LES maintains a pressure of approximately 20 mmHg, with values below approximately 10 mmHg being abnormal. Pressure of the LES 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, ...