Obstructive sleep apnea (OSA) is the most common type of sleep disorder and is caused by complete or partial obstructions of the upper airway. It is characterized by repetitive episodes of shallow or paused breathing during sleep, despite the effort to breathe, and is usually associated with a reduction in blood oxygen saturation. These episodes of decreased breathing, called "apneas" (literally, "without breath"), are at least 10 seconds in length and can last up to a minute or more.
Individuals with OSA are rarely aware of difficulty breathing, even upon awakening. It is often recognized as a problem by others who observe the individual during episodes, or is suspected because of its effects on the body. OSA is commonly accompanied with snoring. Some use the term obstructive sleep apnea syndrome to refer to OSA, which is associated with symptoms during the daytime. Symptoms may be present for years or even decades without identification, during which time the individual may become conditioned to the daytime sleepiness and fatigue associated with significant levels of sleep disturbance. Without a regular bed-partner to notice and make them aware of their symptoms, individuals who generally sleep alone are often unaware of the condition.
As the muscle tone of the body ordinarily relaxes during sleep, and the airway is composed of walls of soft tissue—which can collapse—it is not surprising that breathing can be obstructed during sleep.
Common signs of OSA include unexplained daytime sleepiness, restless sleep, and loud snoring (with periods of silence followed by gasps). Other symptoms are morning headaches; insomnia; trouble concentrating; mood changes such as irritability, anxiety and depression; forgetfulness; increased heart rate and/or blood pressure; decreased sex drive; unexplained weight gain; increased urination and/or Nocturia; frequent heartburn or Gastroesophageal Reflux Disease; and heavy night sweats.
Diagnosis of OSA is often based on a combination of patient history and by Polysomnography, which is a sleep study performed in a sleep lab. A sleep-at-home study can also be performed at home, unattended.
An "event" can be either an apnea, characterized by complete cessation of airflow for at least 10 seconds; or a hypopnea, in which airflow decreases by 50 percent for 10 seconds or decreases by 30 percent if there is an associated decrease in the oxygen saturation or an arousal from sleep . To grade the severity of sleep apnea the number of events per hour is reported on the apnea-hypopnea index (AHI). An AHI of less than 5 is considered normal, an AHI of 5-15 is mild, 15-30 is moderate, and more than 30 events per hour is characterized as severe sleep apnea.