AHI - Supine Position

This measure represents the apnea hypopnea index, abbreviated AHI, calculated only during periods when a person is sleeping on their back. AHI counts how many times per hour breathing either fully stops, called an apnea, or partially narrows, called a hypopnea. In this version, events are scored when they are associated with at least a 3 percent drop in blood oxygen, which is known as oxygen desaturation and reflects impaired oxygen delivery to tissues.

Sleeping on the back often worsens obstructive sleep apnea because gravity pulls the tongue and soft tissues of the throat backward, narrowing the airway. For many people, this position reveals the highest AHI and can uncover positional sleep apnea, where breathing disturbances are much more severe supine than in other positions. A high supine AHI with lower values in other positions suggests that airway collapse is strongly position dependent and may respond to positional therapy, such as side sleeping or devices that discourage back sleeping.

That said, supine AHI can underestimate overall disease burden if a person spends limited time on their back during the study. It also does not capture sleep fragmentation from arousals that occur without a 3 percent oxygen drop, which can still impair sleep quality and cardiometabolic health.