Sleep apnea syndrome (SAS) is a breathing disorder characterized by apneas and hypopneas.
- Apnea: a cessation of airflow for ten seconds or more
- Hypopnea: a decrease in flow by at least 50% for 10 seconds or more
Both apneas and hypopneas are associated with sleep arousal and/or oxygen desaturations of 3% or more.
Apneas and hypopneas result from upper airway occlusion, either full or partial, or from a loss of the autonomic drive to breathe.
There are three types of apnea:
1. Obstructive sleep apnea (OSA)
- The most common type of sleep apnea.
- Occurs when the upper airway occludes (either partially or fully) but efforts to breathe continue
The primary causes of upper airway obstruction are lack of muscle tone during sleep, excess tissue in the upper airway, and anatomic abnormalities in the upper airway and jaw.
2. Central sleep apnea (CSA)
- Is uncommon. affects only 5-10% of the sleep apnea population
- Occurs when both airflow and respiratory effort cease. This cessation of breathing results from a loss of the autonomic drive to breathe
3. Mixed apnea
- Uncommon
- Occurs when an initial central component followed by an obstructive component causes a cessation of breathing
Breathing resumes when the patient has a brief arousal from sleep, of which they usually have no memory. In severe cases, patients may have up to 100 events per hour, resulting in severe daytime symptomatology.
Disease severity is usually classified according to the apnea/hypopnea index (AHI). Measured during a sleep study, AHI refers to the number of apneas and hypopneas per hour.
An AHI of 5 or more generally indicates the presence of mild SAS, and an AHI of 15 generally indicates moderate SAS.
