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Although the condition has been recognized since at least the 19th century, sleep apnea was first diagnosed in 1965. This condition is characterized by frequent sleep interruption because the person has temporarily stopped breathing. Sleep apnea was originally called “Pickwickian syndrome,” after a Charles Dickens character. The character, named Fat Joe, had a condition that caused him to fall asleep while standing up. Its current name comes from “apnea” – the Greek word for “want of breath.”

There are three types of sleep apnea:

• Obstructive sleep apnea (OSA) or hypopnea. This is the most common form of sleep apnea and can occur in all age groups. Soft tissue in the back of the throat can fall back into the airway when a person breathes. Muscles in this area normally work to keep the throat open, but the airway can become blocked if the muscles relax during sleep. When the brain detects a drop in oxygen from not breathing, it quickly sends a signal to the chest muscles and diaphragm to gulp in air. As a result, the sleeper makes a gasping or snorting sound and partially awakens, although he or she may not remember doing so. Snoring – sometimes very loud snoring – is associated with OSA. The risk of OSA increases with stress, obesity, smoking, alcohol and sedatives. Obesity has been noted in as many as 40 percent of cases. Physical characteristics can also play a role. For example, people with large tonsils and tongues, and relatively small lower jaws, are more prone to OSA.
  
  
• Central sleep apnea. This is a less common form of sleep apnea. It occurs when the brain does not signal the chest muscles and diaphragm to breathe. The air passage remains open, but the diaphragm and chest muscles do not function until the person wakes up. This is a neurological, rather than mechanical, malfunction and is rarely seen in people under the age of 60. It is not associated with snoring.
  
  
• Mixed apnea. As its name suggests, this is a combination of the first two disorders.

Sleep apnea is a common condition. Estimates range from 4.5 million to about 18 million Americans suffering from the condition. In the 1990s, there was a 12-fold increase in the diagnosis of sleep apnea. This increase is explained by increased clinical awareness of sleep apnea. Men are affected twice as often as women. A person is considered to have significant sleep apnea if episodes occur at least five times an hour. If they occur 10 or more times an hour, the apnea is considered severe.

Although most of the symptoms associated with sleep apnea are relatively minor, there is a definite link between apnea-induced sleepiness and car accidents. Because apnea is so common, this represents a major health problem.

Sleep apnea is the most common type of condition classified as “sleep-disordered breathing” (SBD). Other types of SBD include:

• Hypoventilation. Continuous but very shallow breathing that gradually leads to low levels of oxygen and high levels of carbon dioxide.
  
  
• Snoring. Forceful, noisy breathing that indicates an obstruction in the airway during sleep. Exceptionally loud and vibrating snoring has also been shown to be a risk factor for sleep apnea. Among women, it has been associated with significant medical risks, including cardiovascular disease and high blood pressure (hypertension).