Swallowing is an active process. The esophagus is not simply a passive tube that allows fluid and foods to pass down by gravity. Indeed it is possible to eat and drink standing on your head! Food is chewed in the mouth and then delivered through the "pharynx" through the upper esophageal sphincter (valve) into the esophagus itself. A wave of contraction by the muscular wall of the esophagus pushes fluid and food down to the lower esophageal sphincter (valve) at the junction with the stomach. This complicated process can be disturbed in many ways.
Disturbances of chewing and getting the food into the esophagus occur commonly in patients with strokes which disturb the nerve supply to the throat. As a medical term, dysphagia is usually restricted to those problems within the esophagus (gullet) itself. These occur because of simple narrowing or blockage, or due to disturbance of the muscular contractions. Narrowing of the esophagus occurs in patients with cancer, and due to scarring after longstanding reflux of acid into the esophagus, often in association with a hiatus hernia. The dysphagia of cancer is gradually progressive and continuous over a period of weeks and months. Dysphagia due to benign stricturing (and resulting spasm) is often intermittent for months or years before it becomes fixed and progressive. When they is any narrowing of the esophagus (or inflammation), sudden obstruction can be caused when a lump of food becomes stuck.
Poor coordination of the muscular contractions of the esophagus cause "spasms," and intermittent brief obstructions (which can be painful).
Dysphagia typically means that the food can be swallowed satisfactorily, but then "gets stuck," at least temporarily. Sometimes the lump of food has to be regurgitated.
When the esophageal lining is inflamed (due to infection or reflux irritation – esophagitis), food and even fluids can hurt as they pass through it – especially if they are unusually hot or cold. This symptom is called odynophagia.
The cause of swallowing difficulties can usually be determined quite easily by simple tests after careful clinical inquiry. Pictures of the esophageal lining can be obtained by an X-ray technique called barium swallow. The patient swallows a cup of thick white barium liquid in front of an X-ray screen. The radiologist can see it travel through the esophagus, noting its shape and any site of holdup. Usually the cause can be determined. Direct views of the esophageal lining are obtained using an endoscope. Upper endoscopy examinations are performed under slight sedation; the lining is seen up close and in color on a television monitor, and specimens can be taken from the esophageal lining for analysis in the laboratory. Some swallowing problems can be treated during the same endoscopy procedure.
Abnormalities of the muscular activities (spasms) can be detected using tests of esophageal motility. These can involve passage of a small tube through your nose into the esophagus to measure changes in pressure. Another related test (24 hour pH monitoring) also involves a tube which detects the presence of excess quantities of acid in the esophagus.