Swallowing disorders (also called dysphagia) are any conditions that cause impairment of the movement of solids or fluids from the mouth, down the throat, and into the stomach.
Swallowing disorders are a significant source of disability. They can have a severe effect on overall calorie intake and nutritional status, and they can adversely affect an individual's enjoyment of eating and drinking and the ability to participate in related social interactions. Swallowing disorders may affect the ability to swallow liquids, solids, or both. In addition to complicating or preventing intake of liquids and solids, some swallowing disorders may make an individual susceptible to pneumonia, if any portion of the substances being swallowed are directed into the lungs.
Many conditions are associated with swallowing disorders. Any condition that interferes with one or more of the three normal phases associated with swallowing will impair an individual's swallowing ability. The three normal phases include the oral phase, the pharyngeal phase, and the esophageal phase. Oral refers to the mouth; pharyngeal refers to the pharynx (the area of the airway at the back of the mouth, and leading to the esophagus and the lungs); esophageal refers to the esophagus (the tube passageway between the mouth and the stomach).
The oral phase refers to the aspects of swallowing that rely on intact mouth functioning. The oral phase is itself divided into two phases, the oral preparatory phase and the oral transit phase. In the oral preparatory phase, solids are broken into smaller, softer bits through chewing and mixing with saliva. The resulting mass to be swallowed is referred to as the "bolus." The oral transit phase refers to the movement of the bolus to the back of the mouth, through the actions of the tongue.
The pharyngeal phase refers to the transit of the bolus into the pharynx, also called the swallowing reflex. During this phase, it is crucial that breathing cease and that the entry from the pharynx into the larynx (voice box) closes tightly, thus preventing food or fluid from entering into the lungs.
The esophageal phase refers to the transit of the bolus down the esophagus and into the stomach. The esophageal phase is guided primarily by a series of involuntary waves of muscular action, called peristalsis, that move the bolus down the esophagus towards the stomach. At the end of the esophagus is an area called the esophageal sphincter, which must relax sufficiently to allow the bolus to enter the stomach. The esophageal sphincter, however, must also quickly resume appropriate muscle tone to avoid allowing stomach contents to exit the stomach and go back up the esophagus (called reflux).
Of the three phases of swallowing, only the oral phase requires conscious input; both the pharyngeal and the esophageal phases occur outside of voluntary control. The amount of time required for the oral phase varies depending on the individual; some people eat or drink very slowly, chewing many times, while others seem to "inhale" their food. Under normal conditions, the pharyngeal phase is over in about one second, and the esophageal phase takes about three seconds. Various disorders may increase the duration (and relative success) of any of these phases.
Swallowing disorders can be caused by the following:
mechanical obstruction at any point along the swallowing path
problems with the nerves and muscles necessary for chewing and moving the food around the mouth
decreased sensation, leading to inability to feel the food and organize its movement appropriately
inability of the larynx to close tightly
problems with coordinating breathing and its cessation
problems with the involuntary muscle movements necessary for moving the bolus down the esophagus
These problems may occur at the actual level of functioning (for example, muscle defects) or at the level of the brain's organization of these functions.