What causes apneas?

Obstructive sleep apnea is caused by temporary and repeated closing of the upper airway.

Obstructive sleep apnea is caused by temporary and repeated closing of the upper airway. Normally when you breathe, the oxygen flows in from your nose or mouth through your airway to the lungs. Your airway is a flexible tube; with OSA, your tongue muscles relax in sleep to the point where the tongue collapses back against the airway, pressing it closed and blocking the flow of oxygen. (Illustrations here of open and closed airway)

Think of a garden hose with a kink in it, blocking the flow of water. If this ‘kink” in your airway were to persist, the event would be fatal. But your brain senses that it is not getting enough oxygen and sends an alarm signal, causing you to partially awaken to restart your breathing. Most people with OSA are never aware of the repeated awakenings throughout the night, although spouses or bed partners may hear the gasping or choking sound when these stirrings occur.