Cycles of Sleep
This describes the stages and cycles of sleep. There are two main categories of sleep:
- Non-Rapid Eye Movement (NREM)
- Rapid Eye Movement (REM)
Non Rapid Eye Movement (NREM)
- Transitional Phase – Between wakefulness and sleep. This lasts for one to seven minutes and is 5% of the total sleep time.
- Light Sleep Phase – This is 50% of the total sleep time.
- Slow Wave Phase (Delta Phase) – A deeper and more relaxed sleep associated with 20% of the total sleep time.
Rapid Eye Movement (REM)
This is a period of deep, refreshing sleep. Eyes move side to side and the skeletal muscles are nearly paralysed which results in a loss of muscle tone in the upper airway. This represents 25% of the total sleep time and is the stage where dreaming occurs.
Excessive Daytime Sleepiness (EDS)
People who suffer from obstructive sleep apnea have a fragmented sleep architecture which causes them to spend an excessive amount of time in the lighter stages of sleep at the expense of the Delta Phase and REM stage. This causes them to have excessive daytime sleepiness due to their lack of sleep at night.
Apnea and Hypoapnea
Apnea is defined as a period of cessation of breathing during sleep for ten seconds or longer. If the patient has more than five episodes of apnea per hour of sleep, this is considered clinically significant and helps confirm the diagnosis of obstructive sleep apnea. Hypoapnea occurs when the decrease in airflow results in a 4% decrease in oxyhemoglobin concentration in the blood.