In obstructive sleep apnea, what event describes a period with no airflow despite ongoing respiratory effort?

• A. Hypopnea
• B. Central apnea
• C. Obstructive apnea
• D. Arousal

Answer: (C)

In obstructive sleep apnea, the defining event is a complete stop in airflow even though you’re still trying to breathe. That happens because the upper airway collapses or becomes blocked during sleep, so air can’t get in despite respiratory effort.

This is different from central apnea, where there’s no breathing effort at all during the pause, and from hypopnea, where airflow is only partially reduced but still present. An arousal is a brief shift toward wakefulness that can occur in response to breathing disturbances, but it’s not the breathing pause itself.

Understanding this distinction helps: obstructive apnea is about an airway blockage with ongoing effort, hypopnea is a partial reduction with effort, central apnea is no effort, and arousal may accompany these events but is a separate response.