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.
Causes and symptoms
A huge variety of disorders may cause problems with swallowing, including:
- progressive neurological conditions (such as Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis, Huntington's chorea, post-polio syndrome, myasthenia gravis, muscular dystrophy)
- mechanical blockage of the swallowing apparatus (by tumors; abnormal tissue growth called esophageal webs or rings; abnormal outpouchings of areas of the esopahagus called Zenker's diverticula; scar tissue or strictures due to radiation therapy, medications, toxic or chemical exposure, ulcers, or smoke inhalation)
- damage to the brain or spinal cord (due to cerebral palsy or after stroke, spinal cord injury, traumatic head injury, or direct injury to any of the structures necessary for swallowing)
- certain medications (nitrates, anticholinergic agents, aspirin, calcium tablets, calcium channel blockers, iron tablets, vitamin C, tetracycline)
- congenital defects (such as cleft palate)
Symptoms of swallowing difficulties include weight loss; dehydration; sensation of having a lump in the throat after having attempted to swallow; drooling; unintentional retention of food within the mouth, despite attempts to swallow; coughing; choking; change in voice; regurgitation of liquids or solids through the nose; difficulty chewing; difficulty breathing or talking while eating, drinking, and swallowing; recurrent bouts of pneumonia.
A variety of tests can diagnose dysphagia. A thorough neurological examination may reveal deficits involving the cranial nerves responsible for the strength and coordination of the muscles of swallowing. Fiberoptic endoscopy uses a narrow lighted scope to examine the mouth, pharynx, and esophagus. Videofluroscopic swallowing studies require the patient to swallow a solution containing barium; a moving x-ray machine takes images to evaluate the swallowing mechanism. Ultrasound studies can examine the tongue and larynx during swallowing. Scintigraphy involves swallowing a radioactive sub-stance, and then examining images to see if the patient is aspirating. Manometry is a test that measures the changes in pressure throughout the esophagus during swallowing, in order to evaluate peristalsis.
Neurologists, gastroenterologists, and otorhinolaryngologists may all work with patients suffering from dysphagia. Speech and language therapists are trained to evaluate and help individuals who have swallowing problems.
Treatment ranges from simple changes in posture while eating to medications to surgical interventions.
When swallowing problems are mild, learning new eating techniques (smaller bites, more chewing) may be sufficient. Therapists can help individuals learn the most effective head and neck posture for successful swallowing. Exercises to strengthen muscles necessary for swallowing and improve coordination may be helpful. In order to improve their ease of swallowing, some people learn to avoid foods with certain textures, to thin or thicken liquids, or to avoid foods or beverages that are too hot or too cold. Medications may help improve swallowing. Botulinum toxin can relax spastic muscle that interfere with swallowing.
When no therapies or medications are helpful, and an individual's nutritional status is seriously compromised, alternative methods of providing nutrition (such as through a feeding or gastrostomy tube directly into the stomach) may be necessary.
Dysphagia can be a very serious condition. Its prognosis depends on how severe the swallowing problems are and how severely they interfere with proper nutrition, as well as on details of the underlying condition responsible for the dysphagia.
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Logemann, Jeri. "Mechanisms of Normal and Abnormal Swallowing." In Otolaryngology: Head and Neck Surgery, edited by Charles Cummings, et al. St. Louis: Mosby-Year Book, Inc., 1998.
Lind, C. D. "Dysphagia: Evaluation and Treatment." Gastroenterolgical Clinics of North America 32, no. 2 (June 2003): 553–575
American Academy of Otolaryngology—Head and Neck Surgery. Doctor, I Have Trouble Swallowing. 2002. <http://www.entnet.org/healthinfo/throat/swallowing.cfm> (June 3, 2004).
National Institute of Neurological Disorders and Stroke (NINDS). NINDS Swallowing Disorders Information Page. November 6, 2002. <http://www.ninds.nih.gov/health_and_medical/disorders/swallowing_disorders.htm> (June 3, 2004).
American Academy of Otolaryngology—Head and Neck Surgery. One Prince St., Alexandria, VA 22314-3357. 703-836-4444. <http://www.entnet.org/healthinfo/throat/swallowing.cfm>.
Rosalyn Carson-DeWitt, MD