What is Sleep Apnea?
Sleep apnea is a disease. In simple terms, it is a repeated decrease of airflow into the lungs during sleep. In uncomplicated sleep apnea, the lungs are normal.
The airflow decreases are episodic. That is, airflow into the lungs is normal except for periods where it drops below a critical level. The drops last at least 10 seconds.
An adult with mild sleep apnea has 5 or more drops in airflow per hour of sleep. In the most severe cases, 100 or more such drops may occur per hour of sleep. Children are a different story.
The figures below illustrate airflow patterns during an hour of sleep.
The middle figure shows 5 significant drops in airflow. In three of the drops, airflow falls to zero. These are apneas. In two other drops, airflow is below the critical level, but not zero. These are hypopneas (hi-pop-knee-uz). The middle figure also shows one non-significant drop in airflow.
Many aspects of the definition of sleep apnea are still debated. We have presented here a simplified introduction.
Next: The two types of sleep apnea: obstructive and central.