Obstructive Sleep Apnea - Pathophysiology

Pathophysiology

The normal sleep/wake cycle in adults is divided into REM (rapid eye movement) sleep, non-REM (NREM) sleep, and consciousness. NREM sleep is further divided into Stages 1, 2 and 3 NREM sleep. The deepest stage (stage 3 of NREM) is required for the physically restorative effects of sleep, and in pre-adolescents this is the period of release of human growth hormone. NREM stage 2 and REM, which combined are 70% of an average person's total sleep time, are more associated with mental recovery and maintenance. During REM sleep in particular, muscle tone of the throat and neck, as well as the vast majority of all skeletal muscles, is almost completely attenuated, allowing the tongue and soft palate/oropharynx to relax, and in the case of sleep apnea, to impede the flow of air to a degree ranging from light snoring to complete collapse. In the cases where airflow is reduced to a degree where blood oxygen levels fall, or the physical exertion to breathe is too great, neurological mechanisms trigger a sudden interruption of sleep, called a neurological arousal. These arousals rarely result in complete awakening, but can have a significant negative effect on the restorative quality of sleep. In significant cases of OSA, one consequence is sleep deprivation due to the repetitive disruption and recovery of sleep activity. This sleep interruption in stage 3 (also called slow-wave sleep), and in REM sleep, can interfere with normal growth patterns, healing, and immune response, especially in children and young adults.