Achalasia is a rare disease of the muscle of the esophagus (swallowing tube). The term achalasia means "failure to relax" and refers to the inability of the lower esophageal sphincter (a ring of muscle situated between the lower esophagus and the stomach) to open and let food pass into the stomach. As a result, patients with achalasia have difficulty in swallowing food.
How does the normal esophagus function?
The esophagus has three functional parts. The uppermost part is the upper esophageal sphincter, a specialized ring of muscle that forms the upper end of the tubular esophagus and separates the esophagus from the throat. The upper sphincter remains closed most of the time to prevent food in the main part of the esophagus from backing up into the throat. The main part of the esophagus is referred to as the body of the esophagus, a long, muscular tube approximately 20 cm (8 in) in length. The third functional part of the esophagus is the lower esophageal sphincter, a ring of specialized esophageal muscle at the junction of the esophagus with the stomach. Like the upper sphincter, the lower sphincter remains closed most of the time to prevent food and acid from backing up into the body of the esophagus from the stomach.
The upper sphincter relaxes with swallowing to allow food and saliva to pass from the throat into the esophageal body. The muscle in the upper esophagus just below the upper sphincter then contracts, squeezing food and saliva further down into the esophageal body. The ring-like contraction of the muscle progresses down the body of the esophagus, propelling the food and saliva towards the stomach. (The progression of the muscular contraction through the esophageal body is referred to as a peristaltic wave.). By the time the peristaltic wave reaches the lower sphincter, the sphincter has opened, and the food passes into the stomach.
How is esophageal function abnormal in achalasia?
In achalasia there is an inability of the lower sphincter to relax and open to let food pass into the stomach. In at least half of the patients, the lower sphincter resting pressure (the pressure in the lower sphincter when the patient is not swallowing) also is abnormally high. In addition to the abnormalities of the lower sphincter, the muscle of the lower half to two-thirds of the body of the esophagus does not contract normally, that is, peristaltic waves do not occur, and, therefore, food and saliva are not propelled down the esophagus and into the stomach. A few patients with achalasia have high-pressure waves in the lower esophageal body following swallows, but these high-pressure waves are not effective in pushing food into the stomach. These patients are referred to as having "vigorous" achalasia. These abnormalities of the lower sphincter and esophageal body are responsible for food sticking in the esophagus.