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Obstructive sleep apnea syndrome (OSAS) is a syndrome that belongs to a group of disorders known as sleep-related breathing disorders (SRBDs). In addition to OSAS, other examples of major SRBDs include:

• Central sleep apnea - a rare central nervous disorder in which the brain fails to send out a normal message to initiate breathing to the muscles that are used for respiration.

• Obesity hypoventilation syndrome - a syndrome related to obesity where a person does not obtain a sufficient amount of oxygen when breathing.

Obstructive sleep apnea syndrome may be defined as a cessation of breathing characterized by repetitive episodes of airway obstruction caused by collapse of the upper airway during sleep. Although originally described more than 100 years ago, OSAS remained an obscure and most undiagnosed condition until modern times. Advances in a specialized area of medicine known as sleep medicine in the 1970s led to increased research interest and far more awareness about OSAS among both doctors and patients.

In patients with obstructive sleep apnea syndrome, the duration of episodes of apnea (cessation of breathing) lasts for 10 seconds or longer and occurs a minimum of 5 times during a specific interval of sleep. Another closely related sleep breathing disorder is know as obstructive sleep hypopnea syndrome. Patients with obstructive sleep hypopnea syndrome have a minimum of 5 episodes of at least a 30% reduction in airflow during sleep that last for 10 seconds or longer but they do not experience episodes of total breathing cessation (apnea) during sleep. Although these episodes of "apnea" and "hypopnea" can be detected and differentiated by polysomnography (sleep test), from a clinical perspective, the underlying causes, signs and symptoms, diagnostic "work-up" and treatment is essentially the same. The term _obstructive sleep apnea-hypopnea syndrome is, therefore, commonly used in the medical literature to encompass both of these disorders.

Classic features of patients with obstructive sleep apnea-hypopnea syndrome include:

• Excessive daytime sleepiness
• Loud snoring during sleep
• Fatigue
• Obesity or overweight