What does your AHI actually mean?

What AHI actually measures.

AHI stands for Apnea-Hypopnea Index. It's the average number of breathing events per hour of sleep:

• Apnea — your airflow stops or drops by 90%+ for at least 10 seconds, usually because the soft tissue in your throat collapses.
• Hypopnea — your airflow drops by 30%+ for at least 10 seconds, paired with a drop in blood oxygen or a brief arousal from sleep.

Add the two together, divide by hours of sleep, and you get your AHI. A score of 22 means you stopped or partially stopped breathing about 22 times every hour you were asleep. For a typical 7-hour night, that's 154 separate events.

The AASM severity bands.

The American Academy of Sleep Medicine defines these standard cutoffs for untreated adults:

What changes on CPAP therapy.

Once you're on CPAP, the score the machine reports is different from the score a sleep study reports. CPAP machines estimate AHI from airflow signals; sleep studies use direct measurement of oxygen, EEG, and chest/abdominal motion. Both are useful, but a CPAP-reported AHI of "4" doesn't always mean exactly the same thing as a lab study AHI of "4."

For treated users, the practical target is AHI under 5 on therapy. Most well-managed CPAP users land between 1 and 5. Above 5 on CPAP, your therapy is working — but it can usually be tuned to work better.

What changes the number.

• Mask leak. Worn cushion → pressure drops → events go up. The #1 controllable factor in CPAP AHI drift.
• Sleep position. Back sleeping dramatically worsens OSA in many patients. Positional therapy devices help.
• Weight changes. Significant gain or loss shifts AHI in both directions. A 10% weight change often shifts AHI by 20%+.
• Alcohol & sedatives. Suppress muscle tone in the upper airway. AHI rises substantially the night you drink.
• Nasal congestion. Forces mouth breathing, which CPAP nasal masks don't compensate for. A full-face mask or chinstrap can fix this.