Apnea

Apnea is a temporary cessation of breathing. It can occur during sleep, result from neurological or respiratory dysfunction, or be deliberately induced.

Obstructive sleep apnea: Repeated pauses in breathing during sleep caused by upper-airway obstruction. The airway closes despite continued effort to breathe.
Polysomnography: An overnight study that records sleep, brain activity, breathing, oxygen levels, and other signals. It identifies breathing pauses and their relationship to sleep stages and oxygen changes.
Hypopnea: A partial reduction in airflow during breathing, often accompanied by oxygen desaturation or arousal. Unlike apnea, hypopnea reduces rather than completely stops airflow.
Sleep fragmentation: Repeated brief awakenings or shifts to lighter sleep that disrupt sleep continuity. Apnea-related arousals repeatedly interrupt restorative sleep.
Central sleep apnea: Repeated pauses in breathing during sleep caused by reduced respiratory signals from the brain. Breathing effort stops because the brain temporarily fails to drive it.
Apnea–hypopnea index: The average number of apneas and hypopneas per hour of sleep. Clinicians use it to quantify sleep-disordered breathing severity.
Dyspnea: The subjective sensation of difficult or uncomfortable breathing. Dyspnea is a sensation, whereas apnea is an interruption of breathing.
Daytime sleepiness: An increased tendency to feel sleepy or fall asleep during waking hours. Sleep disruption from recurrent apnea can cause persistent daytime sleepiness.
Mixed sleep apnea: Sleep apnea episodes that combine obstructive and central features. Some episodes begin with absent respiratory effort and continue with airway obstruction.
Continuous positive airway pressure: A treatment that uses pressurized air through a mask to keep the airway open during sleep. It prevents airway collapse in many cases of obstructive sleep apnea.

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